Thursday's build diary 2

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Thursday:  I braved the rain and wind and went over to the observatory. Where I mounted the 7" OTA without its objective lens. Which saved me lifting another 10lbs at the far end of a 7' tube an awkward 8" in diameter.

Somewhat surprisingly I have managed to center the mounting's axis crossing point exactly in the middle of the dome at 145cm from the north and south support ring timbers. The dome is slightly larger but doesn't count for focuser clearance. Not unless the tube is pointed below horizontal.

With the lower tube mounting ring butted against the tube counterweight bracket there now seems to be plenty of room for me. I'd have no trouble fitting my head between the dome and the eyepiece now. Pushed another 10cm upwards through the rings would bring the OTA central on the saddle. But I'd need to modify the tube's own sliding weight rail. Or mount it on taller standoffs. Or just take it off. The stumpy dewshield would still clear the dome up high but not by very much. I can't take any new pictures because the constant rain prevents me from opening the shutters to get enough light.

Friday is warmer and brighter with only a risk of a shower. I need to mount the 7" objective and tackle the problem of fitting the 6" f/8 alongside the bigger refractor. A second pair of 235mm tube rings, to carry the 6", would need plywood packing arcs to match the 8" tube diameter. The stumpy 6" refractor doesn't suit the spacing of the rings mounted at each end of the cradle.

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Large refractor: Fair warning:

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All of this is just [lots] more words as I ponder all the ins-and-outs of fitting different OTAs to my DIY mounting. The size and weight of these OTAs is not remotely trivial. The deliberate height of the mounting is a problem when fitting OTAs. How else will I be able to look through the eyepiece when pointing high in the night sky?

It is not just a matter of dropping these long and heavy tubes gently into the open rings. It means stepladders and hoists and struggling to reach the upper tube ring, clamping thumbscrews. You can't just leave the telescopes resting in the open rings if the balance is not already perfect. The mounting will want to rotate and the tube to slide downwards. Dropping them would be an expensive disaster!

I'm not complaining. Merely warning those with potentially foolish ambitions. Adding an inch to a classical refractor's aperture is 10lbs minimum extra weight and at least a foot greater length. Most affordable mountings can't cope with refractors of this size because the length. Length means moment. Mass x distance from the pivot. Sadly, your big and heavy lens is on the very end of a long tube.

A 5" is about the limit for most affordable mountings and even then the OTA oscillates every time you touch it. Like focusing for example. Even an "electric" focuser won't help if you touch the telescope with your face or nose while trying to squint though it in the pitch dark. Remember that tall and solid pier just to use the thing visually. Or suffer long seconds of shaking images.

Forget all about imaging unless you have really serious funds available. Like £10k-£15 for the bigger AP mountings alone. Or the skill and stamina to build something seriously big and heavy yourself.

Older mountings, intended for much larger reflectors [like 15-16"] with a minimum of 2" shafts can be updated and restored to take a 7" classical refractor. Think 3" shafts for an 8" or larger. Have you ever tried lifting long, steel bars of that diameter unaided? How big a wormwheel do you need to control literally hundreds of pounds?

The sheer weight and height of these mountings, for comfortable viewing, soon becomes a major hurdle to set up for regular enjoyment. Don't bother unless you have something permanently set up under a decent, weatherproof  cover. Lifting and fitting an 8" refractor OTA is strictly weight lifter [on steroids] territory. 60lbs minimum and 10' long.

Are you feeling lucky? Go and lift a good length of 10" PVC sewer pipe in a builder's merchants if you can find one who stocks pipes of that huge size. Scottish caber tossers might be handy mates to have around if they are sober and live near enough.

The Berry, offset and counterbalanced fork, with Dobsonian bearings, will give you a cheap visual [altazimuth] support. Though only if you make it strong enough. Then you can just drop the OTA into the cradle and start viewing. You'd still need a serious cover and a very tall and very solid pier. Nor will it track Mars as you hoped when you imagined yourself another Percival Lowell but without all of his money.

Tripods are an absolute nuisance with refractors. Because the legs get in the way of the very long OTA when looking high up. The legs would need to have really serious timber cross sections and a really serious head and leg design to work at all. I used hefty scaffolding tube for a tripod in my youth and it was hopelessly flexible for my home made 5" f/15 on a Berry mounting. Even though it still wasn't nearly tall enough for looking high overhead. There was a bright comet high up at the time but I really struggled to see it.

The reason there are so few large classical refractors sold these days not just the supposed false colour. It is the handling of the huge instrument unless properly housed. Take a look at a classical instrument from the past. If you are not immediately awed by the massive iron and bronze castings then you really aren't paying attention.

I would smile when people complained on the forums about their stumpy 6" f/8 refactors being a problem. Until I obtained a secondhand one and struggled to mount it on the sturdy, Fullerscopes MkIII. So it needed a MkIV with its massive alloy castings and 1.25" shafts. A Fullerscopes MkIV is a large and hefty mounting by modern Dinky, Chinese standards. The MkIV is still dwarfed by the massive pier I welded together just to support it.

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Mounting the long OTA [again.]

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Thursday is wet and windy so I can't open the shutters for a working light. Fortunately I have the powerful LED bulb overhead.

I need to add a counterbalance to the focuser end of the long OTA. Logic suggests something more useful than just a big lump of metal. A 50mm finder on either side of the main tube might be a good idea. Though I'd need proper rings to allow alignment with the prime instrument.

I also need to find room for the 150mm OTA for solar H-alpha. Fitting it beside the 180mm [7"] would produce a weird balance situation if the 7" was central on the saddle. Putting it on the outside of the 7" simplifies some of the balance issues but bulks it out and greatly increases the need for more counter-weighting.

Placing the OTAs side-by-side, but on extended saddle crossbars, would work. Or, I could use normal, hinged tube rings to hold both tubes closely together. Though that would be an asymmetric load unless I offset the 7" on the saddle first to compensate. The 6" could then be rotated around the 7" to achieve the optimum position.

Whereas attaching both OTAs directly to the saddle crossbars would be a non-adjustable layout. Will the tube rings for the 7" manage the weight of two heavy OTAs dangling from them! It's a thought. I bought some 8" white, hinged tube rings for my 7" and one of them cracked right across the casting at the hinge! The tiny cross sections here hadn't been given any thought by the [presumably Chinese] manufacturer. I haven't really trusted any tube ring ever since.

Then there is the matter of bringing both focusers together for ease of use and how that would affect the longitudinal balance of the pair. Both OTAs are refractors and typically nose heavy. The 6" would have an extended tail end due to the cantilevered, H-a components. Both would normally use star diagonals for comfortable viewing.

Then there is the matter of adding binoviewing and all that entails. I didn't make much progress on this due to the ridiculous magnifications involved due to the GPCs. [Glass Path Correctors.] Similar to Barlow lenses but more compact. They produce foolishly high magnifications due to their distance from the focus. A claimed 2.8 x is probably closer to 5x in actual use! With a typical refractor focal length the high magnifications demand excellent seeing. Not something which can be guaranteed!

I bought second 26mm and 32mm EPs for binoviewing. Then ended up with two very different lengths of Meade 4000 32mm. One Japanese made and the other presumably Chinese. They have a difference of about half an inch [from memory] in their eye cap lengths above the focuser. Making balancing the images a nightmare! If I buy a third 32mm [secondhand as usual] can I guarantee to get two the same? I haven't found one yet.

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Mounting: Moving the RA wormwheel 5.

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Wednesday: Windy.  After the struggle to fit the PA shaft through the PA bearings I found the motor clearance and position exactly as expected. After all, I had simply inverted the previous layout.

A U-bolt fitted on the top plate of the PA housing would have helped enormously if it supported the housing at the correct angle with the block and tackle.

The remaining shaft length is just adequate to allow a collar to be clamped there with radial screws. Not ideal but manageable.

There is now plenty of room for altitude adjustments via the turnbuckle hidden inside the supporting fork.

I had feared the motor fixing screws would be inaccessible but again there was no problem reaching them with a spanner.

I have yet to try any driven slews but cannot imagine any real problems. The worm/motor housing could do with fine, screw adjustment for a more accurate depthing of the worm in its wheel. I just can't decide on the best way to do it without it looking like a pig's ear designed by a committee.

I have gained a total of [at least] 110mm movement towards the south with these simple modifications. 40mm from moving the central [azimuth]  pivot to bring the round, load spreading disk to the edge of the pier. Another 70mm was gained from bringing the fork tines to the southern edge of the rectangular base plate.

There will be a smaller contribution from lowering the RA Wheel and spacer to the bottom of the PA shaft. Probably another 25mm at a guess. Or about 5" overall from all the changes.

All of which will help to ensure the mounting's C of G [assumed to be roughly where the axes cross] is brought nearer to the center of the pier.  The mounting is twisted to the north on the pier so it is difficult to capture the center in a single photograph. I may have overdone the offset slightly.

The mounting looks taller and slimmer now despite having lost quite some width and a couple of inches in height up at the top. The southerly movement should ensure I can reach the eyepiece of the straight tubed refractor. Hopefully without my head having to displace any more wood than already exists between my ears.

It was very frustrating to have the eyepiece completely inaccessible. Particularly after all the effort that went into building the dome precisely for the [long] 7" f/12 refractor. Which was why I quickly fitted the folded refractor. Then had no chance to do any real observing.

I shall now have to turn a slim, brass, locking collar to stop the wormwheel from [slowly] slipping off the bottom of the PA shaft. Instead of which I found a stainless steel hose clamp as a temporary measure. It saved my nose dripping on the lath at 34F. The wormwheel rotates with the shaft so there is no worry about wear from mutual rotation against the clamp.

Later I dismantled the stepladders and chain hoist and took them back downstairs out of the way. I just need to fit the long tube OTA back on to check the mounting's balance. Then I can try some driven slews.

Click on any image for an enlargement.

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Mounting: Moving the RA wormwheel 4.

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It was pitch black just after 16.30pm by the time I had modified the mounting to take the motor/worm assembly underneath. I used the original center hole despite moving the support fork tines forwards. 

A cross stud would get in the way of new altitude pivot holes 2cm further up. So I moved the holes 3cm upwards instead. The combination of changes gave me lots of clearance from the base plate and the pier.

The images were taken blindly in total darkness with flash. Better images in daylight tomorrow.

Again I used the block and tackle to lift the PA and base plate onto the pier. Screwing the long azimuth clamping stud upwards from inside the pier went surprisingly well. The PA altitude adjustment turnbuckle still fitted despite the changes. I seem to have gained a couple of inches in a southerly direction along the base plate, judging by my rough orientation marks. I'll measure how much tomorrow.

Also tomorrow comes the struggle to thread the PA shaft back down through its flange bearings. Then I can attach the wormwheel and check that all is well. I must surely have overlooked something in my quest to move the wormwheel down to the bottom of the PA. Hopefully the shaft will be just long enough for a shallow clamping collar. I'll probably need a cover of some sort, or a rail, to protect my clothing from the big wormwheel in the dark.

Click on any image for an enlargement.

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Mounting: Moving the RA wormwheel 3.

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Tuesday: Day 2. Another bright but frosty morning. I brought the PA housing down to the floor and did some mock-ups of possible RA motor positions while inserted in the supporting fork. With the RA wheel and motor simply inverted there was no room for the mounting base plate. [See arrow, image right.]

Lifting the altitude pivot hole in the PA housing, by the maximum permissible 2cm, would allow some extra room down below. Moving the whole PA assembly down by 2cm would  be the easiest way forwards.

It would mean removing the side plates of the PA housing to drill them simultaneously on the pillar drill for accuracy. No big deal with the components already down on the floor for easy access without any loads.

The next image shows the effect of raising the PA altitude pivot hole by 2cm. This lowers the PA housing by the same 2cm. Giving me bare clearance between the RA motor plate and mounting base plate. [Arrowed in red.]

By trimming the tops of the support fork tines, on the miter saw, I could move the pivot hole even further towards the N.pole. Which would give me even more clearance for the base plate.  I can reach the correct altitude angle [55°] for the PA when the plates are just touching but would have no leeway for adjustment. It is probably best to move the pivot hole further than the absolute minimum for clearance. Better than having to bring the mounting down again just to drill it a second time.

Click on any image for an enlargement.

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Mounting: Moving the RA wormwheel 2.

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Overnight I can decide how best to move the RA wormwheel down to the bottom of the PA. This would give me about another 40mm of southerly movement. It would also reduce the amount of cantilevering of the Dec assembly off the top of the PA housing. The 2" drop in Dec height will be useful for extra dome clearance up high if I ever need to extend the stumpy dewshield on the straight tubed refractor. Or move the tube so far up through the rings, for eyepiece clearance, that it collides with the inside, top of the dome.

Flashback to 2016 when I was still trying to fit the wormwheel at the bottom of the PA.

The next step is to lower the mounting onto the obs. floor to safely remove the counterweights. Then I can move the 11" RA wormwheel to the lower end of the PA. Then I an try the RA motor mounting plate at the bottom of the RA housing to see if it will allow the motor to fit underneath the PA. Which I still doubt whatever I do to the pier and base plates.

The 10mm thick motor plate will fit in any of the four positions at 90 degrees to each other. I just prefer the motor to be underneath the PA for best protection. Not to mention the tidiest appearance.

The wormwheel and motor assembly will both have to be inverted. The motor support plate pushes the bottom PA bearing downwards by 10mm. Which helps to increase motor clearance from the base plate slightly.

I have tried drawing these changes but would prefer to assemble the parts on the floor to see what is really needed to achieve adequate motor clearance.

Rotating the motor relative to the worm is only possible if it can be tucked in tighter to the wormwheel boss. The worm cannot move relative to its wormwheel. Which makes any changes very limited. Even if there was room for the motor under there it would probably need a longer timing belt. Plus the vital mechanical support for the motor in its new position. A clamping ring will be needed to stop the wormwheel slipping off the end of the PA shaft.

Click on any image for an enlargement.

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Mounting: Moving the RA wormwheel 1.

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Monday: A bright and sunny but frosty day.

First I used the new pulley hoist to remove the folded OTA and stand it on the crate with the focuser safely inside.

Then I dragged both folding stepladders back up to the observatory floor. Where they were opened out and lashed together at the top. Ratchet straps were used as securing guy lines out to the steering wheel brackets. By erecting the ladders E-W across the observatory floor I could still close the shutters if needed. Previously with a N-S ladder arrangement I needed to remove the top crossbars to close the shutters.

I then used the new block and tackle to lift the heavy chain hoist and its burden of chains. To be safely hooked over a 1T lifting strop which was wrapped around the tops of the ladders for further security. Another lifting strop was wrapped around the mounting and further secured with cord against any chance of slippage. All well practiced previously. The mounting weighs a good couple of hundred pounds and destroyed a B&D professional workbench!

Once the mounting was lifted very slightly the base fork's 16mm, altitude bearing and clamping stud could be tapped out through the PA housing. Now the mounting could be lifted completely clear of the fork and on upwards. To be further secured to the tops of the stepladders with cord and more ratchet straps. Not that the chain hoist is likely to give way with its rating much higher than the mounting's weight.

I then removed the central 16mm [5/8"] azimuth pivot stud to allow the base fork to be removed and lifted down manually off the pier. The round base plate was pushed to the southern edge, marked and then I drilled a new, 16mm, azimuth pivot hole. I gained only 40mm [1.5"] mounting movement to the south. Not a lot but worth having for vital dome rim clearance when longer telescopes are pointing low down to the south. The long, straight tubed, 7" f/12 refractor needed a star diagonal just to be used at lower altitudes. I could not place my head behind the bare focuser when looking south over a wide arc.

Now I need to re-drill and tap new threads to fix the fork tines firmly to the rectangular base plate. The square section, PA housing sits tightly and is firmly clamped between the tines so they cannot possibly tip sideways. That is as far as I managed to get before I drove off to collect my "observatory" clock after its badly missed delivery. By 30km or 20 miles!

Click on any image for an enlargement.

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Observatory: The perfect observatory clock?

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I think I have finally found a perfect observatory clock after searching endlessly online:

 A relatively inexpensive, LED, wall mounted plate ~ 30 x 12cm, in black plastic. With large, 2" high, illuminated, red batten numerals and seconds indication.

Intended for public spaces like lecture theaters and classrooms, it runs on 5VDC from a mains wallwart. A DIY battery pack would be an ideal option to avoid having mains running constantly to keep the clock to time. I don't wear a watch any more and an unlit dial is just a complete waste of space in the dark. I hope to have the clock delivered in the next couple of days. Images and details to follow.

Now take a deep breath: Monday morning: I check the tracking for my clock parcel. For some reason the stockist had changed my postcode to another 30km away with the same street address but added a different village name! So I rang the parcel service and told them of the situation. They told me to contact my supplier. So I rang the supplier who said they would send an email to the parcel delivery company.

Since this freight company couldn't deliver, because the imaginary customer wasn't at home, they delivered it to the nearest parcel collection point. Still 30km from my home address for which service I had paid £10 equivalent for home delivery. Then I received the confirmation by both SMS and email that the parcel was waiting for me 30km away. Nice! So much for contacting two customer services.

What to do? Wait for another two, or more, days while they collected the parcel and resorted it to the correct delivery address? Still with the wrong village name and still with the wrong postcode and therefor very likely to be wrongly delivered ad infinitum.

So I rang the parcel collection point to confirm it was still there and then drove the first half of the 60k round trip to pick it up. To find that the staff had changed and they knew nothing of my earlier phone call.

I now have my clock at home but my camera can't cope and just shows bright orange-white numerals. The true colour is a very even, bright blood red with flashing colons. I'll try photographing it again in daylight tomorrow.

Somebody overlooked the fact that you can set the hours and minutes but you can't set the seconds. They keep changing whatever I do. Guess what? The clock doesn't stop when the 5V power supply is switched off. So I can't even reset the seconds by switching it off. Grr?

Further experimentation with the three setting buttons suggested there is a brief pause in the seconds while the minutes are being advanced on Button 'B' but this probably requires a 12 hour advance. Am I having fun yet? The numerals are actually 1.75" high so I was almost correct with my scale guesswork from the manufacturer's sales image.

The Maker's name is Manutan [of France] but the clocks are really made in China. The French website claims a 10 year guarantee but there was no paperwork to that effect in the box. Simply a multi-language instructions sheet.

Obviously intended to hang from a wall thanks to two large recesses on the back. Raised, perimeter studs on the back allow the PS cable to reach the socket without pushing the clock untidily off the wall.

The online cost was about £45 equivalent in Denmark plus postage, plus hair loss, plus petrol for 40 miles of unnecessary travel and numerous phone calls. I quite like the clock. A lot. I just hope it doesn't mind being frozen during the long Danish winters. The PS says "indoor use only." Is an unheated shed considered normal use?

I unplugged the PS overnight and discovered that it restarted to the same second when matched with the Windows clock. There must be a hidden battery somewhere inside to keep the chip running. It might be fun to convert it to read LST instead of "normal" time but I missed that class.

Click on any image for an enlargement.

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Mounting: Return to Goto norm?

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Thursday: I decided to try again with Cartes-Du-Ciel and noticed that Com1 was chosen instead of Com 3. So I changed it to Com 3 and slews began immediately. For some reason AWR thinks my telescope is upside down on the mounting and this information is being passed onto C-Du-C.  Syncing on Polaris did not help the cause and the telescope ran backwards to a target in the West instead of the East.

So I lifted the telescope off the mounting, with the new pulley hoist and reversed the cradle. The best attachment point for the hoist on the folded refractor has yet to be established. I shall get back to it after a pause for lunch.

Inverting the cradle worked after a Sync on Polaris and confirming. C-Du-C doesn't always register a Sync on a target object. Though it was interesting to see how it went the long way around to ensure the telescope was on the correct side of the pier and the right way up after a long Goto slew. Not such a problem with a refractor but a reflector would really hate to be inverted!

I deliberately and repeatedly chose opposite horizons to see how the Gotos would cope in getting to the new target. C-Du_C now thinks the telescope is the right way up on the cradle. I found a telescope inversion setting in C-Du-C last time but can't find it now despite endless searching. I can't be certain, but it seems Goto slews in C-Du-C are even slower than IH2 handset button slews. I measured roughly four minutes for 90° before I got bored with counting aloud. One thousand, two.. Retried a Dec slew with a real clock sitting on the desk. Two minutes for slightly more than 90°.

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Observatory: Lights and OTA hoist pulleys.

Tuesday: A cold day @ 40F with gales and showers. Which meant repeatedly closing the shutters to keep the rain out.

Rewired the overhead lights. One white bulb and one red on opposite ends of the top crossbar. I have used plugs and sockets to isolate each of them individually when not required. I thought of having a mains cable rising from above the mounting to avoid dome rotation conflicts. This might work with a hollow PA but mine is solid. Leading a wire over the outside the mounting would soon tangle with the telescope or the mounting itself.

This later image shows the 5mm rope size, 17mm Ø, original, micro-blocks below the 6mm rope, 22mm Ø blocks for scale. The difference in friction, when using 5mm rope with the larger pulley blocks, is literally night and day.

I stripped the rope from the 3x3 micro-pulley system and re-threaded carefully to maintain straight runs between pulleys. Still the friction was as bad as the dirt cheap pulley system with its thinner cord. The falls of rope [throws] were rubbing against each other. So I untwisted the system and maintained it that way. With my hand through the runs while lifting and lowering.  This was an improvement but not by much and was far too awkward for real lifts.


I was only using a 5kg weight for my trials. Which may have been far too low to stretch the system to a normal level of efficiency. The breaking strength is claimed to be well over 500kg for both the 5mm rope and the triple pulley blocks. Higher loads would probably tension the rope to take out twists and might even reduce the working diameter of the rope itself.

Boat owners surely wouldn't put up with the levels of friction I observed with these small commercial blocks. The pulleys are fine with very easy rotation. The problem lies with the multiple falls of rope being packed so closely together by the tiny, triple blocks.

I have now ordered a pair of 6mm triple pulley blocks for use with the same 5mm rope. Ever the optimist! I can go and pick them up from the parcel shop today and give them a try. As mentioned above, the difference in friction was truly startling. Just the weight of the free [pulling rope] was enough to make the lower [travelling pulley block] rise! Of course I am absolutely delighted with the ease of movement now. I'll try running thinner cord 4mm on the micro-blocks as a reserve system.

The rope diameters are nominal but there is no reason to use the maximum size. I have been doing a lot of online research regarding pulley systems. Some pulley block makers suggest 1:8 rope to sheave diameter. My mini-blocks were even less than 1:3. [5:12mm] 5:22mm is over 1:4. While 5x8= 40mm which is about the size of the dirt cheap system's sheaves.

I could have tried longer bolts and fitted spacers between the pulleys, on this cheapo set, but had no desire to be working on the lathe in such miserably cold conditions. I had already swapped to longer bolts and fitted Nyloc nuts because the original, plain nuts kept falling off!

This cheap and rather nasty block and tackle is widely sold around the globe. It works, but the friction of the rollers is much higher than the gorgeous, polished stainless steel, boating kit. The thin, original, stranded cord was unpleasant to handle and easily frayed. Making using it a bit of a pain without thick leather gloves. While the 5mm boating cord is an absolute delight to handle and any tangles soon drop out by themselves.

Click on any image for an enlargement.

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Folded refractor: Cleaning, balance and alignment.

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Sunday: 38F. Removed the OTA and [carefully] cleaned the 7" objective lens in its cell. Then remounted it over the stub dewshield. I shall have to attend to the OTA balance on the mounting. This was immediately improved by adding a longer spacer behind the counterweights. There is still some weirdness about the OTA's own balance. It isn't remotely symmetrical. Preferring to be one way up but not the other. All this throws unwanted loads onto the drives when slewing.

Monday: I have to collect my new compact pulleys from the local parcel shop. Hopefully these will offer lower friction when lowering OTAs. Collected, but they are quite tiny so difficult to thread. Despite which they run very freely on the 5mm rope once the ropes are in place. Provided, that is, the ropes do not cross.

The answer seems to be to organize the ropes with the pulleys quite close to each other. Then, once the are separated they will have a minimum of rope crossings. I'm very tempted to buy the next larger size for more separation and greater freedom between the pulleys. These things really are almost jewel-like in appearance with their shiny stainless steel.

I fixed a 2 meter [6'6"] long alloy pole to the OTA to check dome clearances more easily as I slewed around. Only to discover that ideally I need to move the mounting base a full 30cm [12"] to the south to be dynamically symmetrical with the dome.

The big GEM's natural offset pushes the center of rotation [where the lines of the axes cross in the Dec housing] well to the north. The heavy support fork leans the opposite way but the PA leans north too.

Quite how this bodily movement of the mounting will be accomplished is quite another matter. Extending the thick plywood, top plate of the pier would be dead easy. But then the lower halves of longer telescopes would hit the pier when pointing up high. Which is a complete non-starter unless more frequent meridian flips become acceptable.

I could chop off the pier at floor level and add a tubular pier top somehow. Or, even make a leaning top section if it would help. All this assumes that I can still climb the internal stepladder up through the pier. Which can't be taken for granted with most pier modifications to the present, hollow, pyramidal section. The larger square, formed by the pyramid at lower heights, could be used to offset a tubular pier extension.

A suitable counterweight at the focuser end would solve most of my mounting's spherical asymmetry. The weight would allow the straight refractor to be shoved much further up through the rings. Though that wouldn't help with the 10" f/8 Newtonian mirror waiting patiently for its latest reincarnation.

I had rather imagined a parallel layout in the same, square section, Porsa tubing as the folded refractor. Fixed side by side on the big GEM they would be absolutely massive! Over 6'6" x 2' x 1' in Olde Money. Or 2m x 60cm x 30cm in New Fangled.

Another way of reducing the northerly bias [slightly] is to move the 11" wormwheel to the bottom of the PA. This would move the axis cross about an inch and half south and lower it about 2" into the bargain. The downside is finding room for the worm and motor assembly, lower down, even if the wheel missed the mounting. Which is why I never bothered to pursue that particular layout at the time.

The worm assembly could be mounted on top of the PA housing but it would look very 'untidy.' Not to mention its vulnerability to knocks and bumps during fitting and removing OTAs.

The mounting base would have to be completely redesigned to find room underneath the 11" wheel for the motor and worm. Unfortunately I haven't found any more 20mm scrap aluminium. It is very unfortunate that I so badly misjudged true north when planting the foundations for the pyramidal pier. The mounting is badly skewed on its plywood platform. Which means chainsaw wood butchery to find room for the motor underneath.

Extending the pier's top plate south, even by a couple of inches, would make much more room underneath. The image gives a rough idea of what is needed. Had the pier been rotated north the entire octagonal building would have had to follow suit. Or the entrance doors would probably have been obstructed by a pyramid leg.

Putting the motor/worm assembly on the side of the PA housing is also possible but would probably look like an extremely clumsy afterthought. I'll have to continue to mull all the possibilities. Leaving a problem to stew unsupervised often produces a much better final result.

Aha? The tines on the mounting's supporting fork could be shifted a couple of inches south. That would mean drilling and tapping new holes from underneath. It would certainly provide lots more clearance from the hefty base plate to allow the worm/motor assembly to be hung underneath.

The motor/worm support plate would be moved down too. Once inverted it would provide exactly the same drive geometry without any other change. Then the entire mounting would be moved to the edge of the pier plate. Another couple of inches gained towards the south.  Probably leading to 6" overall?

That is around half the present northerly bias of the Dec/PA crossing point. Moreover, the mounting base plate would see a much more even load. At present the load is cantilevered outside its own footprint towards the north.The gain would mean I could use the straight tubed OTA without hitting the dome support ring. And/Or reduce the necessary counterweight required to balance the typically, nose heavy refractor.

This would mean having to disassemble the heavy mounting components, the gains might be worth all the effort. The head conjoined, folding stepladders and chain hoist would be needed for increased safety. I'm not sure I can trust the block and tackle just dangling from the top of the dome. Even if the dome survived it could open up all of the panel joints.

It all looks so easy until I measure the height of the worm/motor assembly's overhang beyond the PA housing at 12cm.  Finding room underneath the mounting plate is too problematic. The Astromount[UK] puts the motor on the side of the PA housing but I think it would make mine too vulnerable to collisions with the OTA.

Click on any image for an enlargement.

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First [Red] light in the observatory.

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I was able to fit the new plate, with the lens already mounted, as dusk fell. The I used the pulley system to lift the folded OTA onto the mounting. Only to discover that the balance was all wrong. I shifted the sliding weights forwards and things settled down. More to do on getting both axes balanced with the worms freed. Refitting the modified OTA was a bit rushed but I was able to overcome the difficulties. The pulley system allowed most of the weight of the OTA to be taken up while I aligned and dropped the fixing bolts through the cradle.

As I was slewing the OTA to the Moon the drive pulley started slipping on the axle of the RA stepper motor. Grrr! I had fitted a second clamping screw during the first build but it obviously wasn't enough. Or the grub screws had simply worked loose. Not much I can do about that without removing the motor from its housing.

Nevertheless I managed a couple of hours looking at the Moon and Mars while I fiddled with optical alignment and compared different drive speeds.

Still quite a bit to do in the alignment department too. The Cheshire EP suggests the objective was already quite well aligned but the mirrors are off after the removal and refitting of the OTA.

The 1W red LED light bulbs are proving about right once I am dark adapted. The trapdoor is flooded with red light from the LED bulb inside the pier to show whether it is open or closed at a glance. I could add some white paint or similarly reflective surface to the underside of the hatch to emphasize when it is open in poor light.

The chain of red Xmas lights is proving handy to delineate the edges of the space available. They do produce a useful glow once I am fully dark adapted. Only just enough to see if I have put something down on the top ring.

I think I shall hang one red LED light bulb up high to supplement the white one. Which is normally turned off but handy for maintenance work. A red, even glow might be best without having the bulb too close to my eyes. I was able to dark adapt despite the red bulb [temporarily] hanging off the mounting but a more general red light might be worth trying. Provided I hang it beyond the top crossbar there should be no conflict with seeing the night sky through the open slit.

I used the familiar "North pole pointing" alignment so that the OTA wanted to rest naturally on the cradle. The tightness of the lifting pulleys prevented easy lowering but the new pulley  system will hopefully help here. I'm glad I ordered a 3x3 system again because having fewer pulleys would take away the relaxed hold needed on the rope.

Remembering to hold onto the rope while manhandling a very awkward, 40lb telescope, high above my head should not need to increase the difficulties. I'm still supplementing the stepladder with an old beer crate. A plywood box with three different working heights would be preferable. The crate offers only one and is finally falling apart. The stepladder is too bulky and awkward in the dark but essential some of the time.

All in all it was valuable experience in using the observatory in the dark for the first time. Until I actually tried it I had no idea about some of the problems I'd face. A red cover for the torch would help.

Now I need to remove the RA stepper motor and drill and tap the small timing pulley boss for a third grub screw. Then bore a deep hole right through from the edge of the front plate. This will allow a long series hex driver to tighten the grub screws without unnecessary dismantling. I did this for the larger pulleys and it has proved invaluable. The pulley grub screws would otherwise be completely unreachable. Dimpling the shafts with a drill might help too if I can keep the swarf at bay.

Update: I dismantled the entire RA worm/motor assembly and drilled the front plate on edge to allow easy tightening of the small pulley grubs screws with a hex key. There were already three grub screws which I had forgotten about since building the mounting. The larger pulleys already have tightening access holes. I replaced the motor and have just spent an hour looking at a rather soft Moon. Thin cloud is moving in.

I also fitted the 1W red LED bulb overhead and it is proving just right for flooding the dome with dim red light. Handy for seeing what is happening to the telescope during slews. I can still see faint stars when looking just past the red bulb. I shall hang the white light on the other side of the top crossbar for maintenance moments in the dark or when the shutter doors can't be open. It is odd how different the dome looks and appears inside in changing light.

Click on any image for an enlargement.

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Folded refractor: New 10mm front plate.

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As mentioned previously, the objective bayonet system worked but hindered collimation due to clearance problems. There was just not enough room between the plates despite the thick felt pads. So nuts would push or pull against the plates.

My first attempt at cutting a 198mm hole was done by chain drilling a circle of small holes and then opened out with two larger sizes of drill. Each larger drill narrows the metal between the holes. This seemed to go well until the router wanted to take more metal to clear all the previously drill holes. So the hole ended up much too large by the time I had re-cut it twice more using different pilot holes in the router base plate.

So I started again with another scrap aluminium plate. This time I went straight to the router without bothering with drilling all the holes. I took a couple of shaving cuts first and measured the diameter carefully before proceeding. Despite the arcs measuring rather small at first it actually ended up 1mm larger. Which was perfect for my needs in just clearing the back of the iStar objective cell. Which is rather mean in diameter. With barely enough room for the collimation screws to get any purchase in the backplate. At least, not if the mounting hole is made larger than 199mm Ø. 200mm would be too big and the collimation screws would eat into the hole!

During the cutting I had run some screws directly into the workbench in holes provided in the scrap plate. With thick washers sandwiched to lift the plate off the top surface. Otherwise the router bit will take a circular bite out of the top surface of the bench. 

I used a rather tired bit in the router which made for rough cutting if I lowered the cutter by more than a millimeter. Adding a few drops of lamp oil into the groove between cuts helped keep the revs up and the roughness down to a minimum. Then I just kept going round and round with the router cable held above my head with a pole through the hedge.

Now all I need is to mark, drill and tap the plate for the collimation "pull" screws. Followed by sawing the plate to size on the sliding miter saw. With a final going over with a sander to to tidy up all the roughness. Another clear night is forecast. So I had better get on with it!

Click on any image for an enlargement.

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Observatory: OTA hoist.

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Thursday: The weight, size and reach required for my rather large telescopes demanded a much safer way to fit and remove them from the mounting. I had been using a stepladder with my feet about 4' above the floor. Not ideal as my balance was all wrong as I hung over the top of the ladder.

The folded refractor bayonet system was not proving ideal. Fortunately and I had a piece of scrap 10mm aluminium which could replace two thin plates with a single stiff plate. That meant the OTA had to come down off the mounting again so I could work on it more easily.

Chain drilling the scrap plate took much longer than expected. I did three circles using larger drills each time. Then broke through the remaining bridges with the oscillating cutter and a bi-metal blade. Next step is to use a [wood] router to smooth the 20cm diameter circle using a simple plate jig with central pivot point. It was a clear night with moon and Mars but I had no instruments mounted.

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I have had a dirt cheap block and tackle system for years. This would do as a hoist and I had previously upgraded the original cord to something stronger. It just needed somewhere safe to hang it.

This required I lift my two-stretch ladder into the observatory to reach the top of the dome. The folding stepladders having already been taken down. Then I drilled through a reinforcing plate at the top corner of the observing slit and fitted two eye bolts  right through the doubled 3/4" cross board.

In the interests of a belt and braces approach these two eyes were joined by a sturdy bolt secured with lock nuts. If one eye bolt should fail then the other provides a bit of extra insurance. Two eye bolts would not be loaded as much as a single one anyway.

A stainless steel caribener was used to hold the hanging plates of the top block of the pulley system. The 3x3 pulley system requires very little effort on the cord to lift or hold the folded OTA. I would not trust the system with the heavy mounting but it is perfectly adequate for any of the 30-50lb OTAs I'd ever need to mount. 

I suppose I could hang a loop  of stronger rope from the top to see if the eye-bolts would take my own weight. The dome's top cross board would easily take my weight when I hung from it while I was still working down on the ground.

Update: I have ordered two new triple [yachting] mini pulleys and 30 meters of 5mm rope to make a completely new pulley system. With a much higher claimed breaking strength this should offer a much safer means of lifting OTAs on and off the mounting. The present pulleys are very stiff on their axles. Which increases friction both when lifting and paying out rope. The cost is around £50 equivalent so is relatively small beer, long term insurance compared with the cost of dropping an OTA!

It is a mild 50F, sunny day with a light breeze so I am airing the dome to see if it helps with the sooty mold.

Update: Oxalic acid has been suggested for removing the mold. [See comments.] Unfortunately its toxicity, even in small quantities, makes it an unlikely choice for this job. My wife [The Head Gardener] wouldn't even let me use household ammonia in the dome. This is another widely recommended treatment for mold on wood. The problem is having to work mostly overhead with poor access from ladders. I could bring back my folding stepladders but the wear and tear of working on the building on a daily basis has made my hands and arms increasingly painful. [AKA: Tennis elbow.]

We will soon be descending rapidly into far more typical, cold, Danish winter weather. So natural evaporation becomes much weaker with time. I have been keeping the dome and observatory doors wide open all day to aid drying. With no obvious effect so far despite the mild weather and sunshine.

The next plan is to use more brown soap but using hard sponges [instead of soft] and rinsing with water with a little washing up liquid. Another suggestion from the internet. A heat gun has also been suggested but I have never owned one. The dome is so [deliberately] draughty that I seriously doubt a 2kw fan heater would raise the temperature much. Localized warmth [from a heat gun] sounds far more sensible. I might even get a sense of revenge on the mold for the uninvited invasion.

Just think, I could have had an all aluminium, barrel dome a full year ago. If only a local engineering company had taken my order for rolling four aluminium half circles in angle profile seriously.

Click on any image for an enlargement.

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Mounting: Balancing properly.

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After wasting a couple of hours carefully making a 1mm thick, plastic disk shim it proved not to be needed. My worm shaft measurements with a straight edge in the semidarkness were false. Today in bright daylight I used a long jawed, Vernier caliper and discovered the original worm height was fine. Trying to slew with the worm now set too high merely resulted in endless noisy stalls. Removing the shim again returned the drive to a peaceful normal. 

During my levering operation to make room for fitting the split ring shim I discovered the mounting balance was poor. Loosening the wormwheel clutches was not nearly enough. There was still too much friction to judge the balance properly. I was just fooling myself. Imbalance is very obvious when you learn how to do it properly.

Slacking off the worm assembly freed the shaft completely. The OTA now proved to be too light compared with the counterweights. Adding a half kilo weight [1lb] to the outer OTA frame almost neutralized the imbalance. After that the RA drive would slew 180° using the IH2 Handset without noise or complaint. Unfortunately even Cartes Du Ciel won't connect with AWR-ASCOM now.

I have now wiped grease all around the wormwheel teeth with a rubber glove clad finger. Just adding lubricant to the worm alone hadn't made it spread visibly along the wheel rim. 

It was quite breezy today and the shutters kept opening or closing by themselves. I'll have to add sliding bolts to the bottoms of the shutter ribs.

Just as a local experiment I have washed two mold-blackened plywood panels with brown soap. Then rinsed off with a sponge and clean water. Finally drying them off with paper towels. Many of  dome panels are going  dark but do not look as if they are sourcing rain from the outside joints. The mold often appears as patches in the middle of the panels. Perhaps the covering paint has trapped moisture from rain in the previously exposed plywood? The lightweight tarpaulins were very poor protection.

Some panels are completely untouched. As are sheets of identical but unpainted ply resting in the lower observatory building. There is certainly no shortage of ventilation in the dome. The weather is remaining damp but rather mild for this time of year at around 50F/10C. I don't feel it would be safe, nor sensible to paint directly over mold. The humidity reading is maxing out at 35% on the inside of the panels. With the remaining timber construction much lower.

Wednesday: Under a horrendously overcast sky I aimed the 7" folded refractor at some distant trees to check image quality. It was surprisingly good. I would easily have seen flies on the leaves had they been present. I used the IH2 handset to pan slowly across the tops of the woods.

It is surprising how the appearance of the dome changes constantly with the light and the weather. I must admit to a preference when it looks completely matt and smooth due to frost or heavy dew.

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Mounting: Worm adjustment and Goto drives.

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It needed careful and repeated checking, using a straight edge above and below the wormwheel and feeler gauges. Eventually I was able to confirm a 1mm error in RA worm height relative to its wormwheel. Unfortunately the worm is set too high and this cannot be reduced.

The worm housing bracket sits on top of a solid plate and square section tube housing the drive, stepper motor. I used 10mm, solid aluminium plate everywhere to reduce flexure to a minimum. Only milling away the plate would reduce the worm's height. Needless to say that isn't going to happen.

Normally, correcting this height error would mean removing the OTA and dismantling most of the mounting to fit a thin, ring shim [large washer] under the wormwheel boss.

To avoid dismantling and heavy lifting, a split shim would obviously be best. 1mm is pretty thin. So most sheet materials could easily be flexed enough to allow a simple slit and circular cut-out to pass easily over the shaft.[50mm Ø] It would just require a sufficient gap be opened below the wormwheel boss to allow the shim to be flexed enough to be slid into place.

It might have been an interesting exercise to work out the desired friction levels between rotating surfaces on the shafts. Early on I tried PTFE [Teflon] between contact surfaces to ease manual pointing.

In practice both shafts rotate uniformly from end to end entirely under the Goto drives and motor driven slews. No manual slewing is allowed. Or the lock on the sky is completely lost until it is re-set with a Sync on a known object or position. Even here it is assumed that the mounting is perfectly set up on the True Pole and the Declination shaft is perfectly at right angles to the RA.

An observatory, with a supposedly immovable pier, should offer the opportunity for better mounting alignment. Since its alignment is not repeatedly undone by tearing everything down at the end of an observing session. The telescope itself should also be parallel to the Declination shaft. Or yet again, Gotos will be relying on false information.

The AWR-ASCOM Goto system relies entirely on counting motor turns. Any slippage of [purely protective] clutches would not be sensed. Leading again to false telescope positioning on the sky. The drives are essentially, completely blind. So must carefully count the exact number of "footsteps" between landings on known objects.

There is no GPS or shaft encoding involved. Only a friendly mouse click on the computer screen, or handset button, to confirm arrival on the chosen target. The IH2 handset offers four different speeds of drive to adjust discrepancies in centering before a Sync is confirmed.

The clutches are supposed to protect the motors if they should stall under an unbalanced load or physical blockage. All too often the long OTA would slouch downwards due to imbalance. Leaving me, yet again, with lost coordinates.

You can't ever physically nudge the OTA safely onto the target. The handset [control paddle] must be used to slew to the target. This takes some getting used to after decades of manual shoving telescopes around the sky. The AWR handset is far more responsive and useful than the Fullerscope's synchronous motor control paddle.

I soon fitted three radial screws and plastic clutch plugs to both wormwheel bosses instead of the original one. Even when these are very firmly tightened the OTA can still move independently of the drives rather too easily. Adding the binoviewer or a 2" star diagonal would cause a major slippage simply due to a sudden change in the OTA's balance.

I have been steadily improving the balance and reducing the mounting's sensitivity. Hence the change to the folded refractor instead of the long, straight tube. Moment is mass x distance from the fulcrum [or shaft in this case.]  Sliding weights became essential to combat these sudden shifts in moment whenever a perfectly normal accessory was added.

A routine in setting dynamic balance weight positions must be established to cope with these perfectly normal changes. Otherwise the mounting will count the paces to Go To the butchers. When it thought it had safely reached the bakers.

It only thought it knew where it started but was really facing the wrong way. Sadly it can gather no clues along the journey to remind itself exactly where it is between landing points. Only a fresh Sync to confirm safe arrival at the next target will help.

None of this is easy with a telescope of this scale and weight and often so far above the floor of the observatory in the dark! It is a steep learning curve even when I thought I knew what was involved.

The masses and the torque to overcome them, or to resist unwanted movement, must be carefully balanced in all planes. I still feel I have hardly started on the journey to event-free observing. More practice with a solar telescope in daylight will help to iron out the problems and build valuable experience in the mounting's foibles.

As yet I have no real observing experience with the big home made mounting. Just getting the drives to work with a planetarium software has denied me useful practice with pointing the telescope. Perhaps if it was too easy I wouldn't learn how to cope with a problem. How grateful I should feel about this forced learning curve is another matter.

Monday: I bought some smooth, white, Hammerite paint for the counterweights today. I did not paint the turned edges after smoothing the casting excesses [flashing] in the lathe.

They were cheap, 2" bore, 5kg, "Olympic Standard" weightlifting disks in rather rough cast iron. Their size was carefully chosen to allow them to just fit in my old lathe. Even so I had to use a reversed boring bar to reach around the sides from the tool post. I have watched the edges slowly rust ever since without getting around to painting them. I chose white paint for maximum visibility in low light conditions.

Click on any image for an enlargement.

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Folded refractor: Optical collimation.

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It is some time since I last tried to collimate the iStar 7" [180mm] f/12 R35 refractor. Which might explain my difficulties in trying to align the optics. [collimate] Struggling to reach the objective's collimation [push-pull] screws with the short dewshield in place was becoming a bore. Nothing I tried with the screws seemed to change anything in the torch reflection from the objective that I was seeing through the empty focuser.

So I removed the dewshield and immediately discovered my problem. My fear of the objective falling off the tube adapter had driven me to fit Nyloc nuts to the cell's tension screws. These nuts were jammed between the two bayonet plates. The objective had to come off the bayonet plates. Which meant removing the plates from the OTA.

Guess who forgot the balance of the OTA without the objective in place? As soon as I removed the heavy lens the OTA did a somersault. It nearly hit the objective out of my hands but somehow I clung on.  

I drilled the marks where the nuts had been rotating against the rear bayonet plate. Now the nuts were free to move inwards and outwards. Re-assembly, without the dewshield, resulted in my being able to collimate with clear changes after each cell screw adjustment.

Remembering which screw did what was quite another matter after a tour around the mounting between each trial adjustment. Eventually all the reflections overlapped as I moved my eye around the small LED torch I was holding in the focuser.  A subsequent check with the Cheshire in the focuser confirmed that all the reflections were hidden under the cross-hairs.

I'm now looking at ways to attach the dewshield without trapping it behind the objective cell. There should be enough meat in the rear rim to allow me to trim a larger hole. While still allowing me to make screw holes to fix it independently to the backplate.

The sharp eyed will notice the damp and sooty mold on the inside of the plywood dome from condensation. I have researched the issue and will try a bleach solution. Forum members were polarized for and against painting the dome inside.

Click on any image for an enlargement.

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Mounting: Drives continued.

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A wet Saturday: First I set up a low energy bulb right at the top inside the dome. It was a day of heavy showers so I couldn't leave the shutter doors open for useful working light. I fitted a plug at dome ring level and a socket just below. So I can simply unplug to cut the power to the light or when I have to rotate the dome. The light cable was clipped to a shutter rib to keep things tidy. I need to get more cable clips.

Later I moved the AWR IH2 handset supports to the East side of the pier. Sited just above and to the right of my laptop screen, I now have all the information and buttons right in front of me. I also moved the laptop shelf out enough to allow cables to drop freely down behind. Rather than running across the top of the shelf. Now the mouse has room to move freely.

Siting the controls in an observatory is important. Particularly when dealing with solar observation and imaging. Reflections of brightly lit backgrounds can make a laptop screen almost illegible. I reasoned that the sun would light up the southern wall more than the east. A black, light shield for the screen will help. I'll only make one after a bit of experience to confirm exactly what is needed.

Then I spent some time Syncing and Goto Slewing using Cartes-Du-Ciel. I'm finding my way around the C-Du-C charts and buttons while Stellarium completely refuses to cooperate. I'm not sure why C-Du-C can't have Sync under both Telescope menus or even a dedicated "button." The right click Telescope menu doesn't show it. Only the main Telescope heading above the chart.

Cancel Slew is important too when the telescope tries to go "the long way around" with several nerve wracking "fairground ride" headstands thrown in. At least the noisy motor stalls have dropped to only an occasional graunch thanks to improved balancing.

The torque available is mind blowing. There is no way I can physically stop or even slow the worm shafts with finger strength alone. Multiply that by the number of teeth on the large wormwheels. [287] and you should be able to lift the dome off its rollers.

Which leaves me wondering what could possibly cause a stall. I have the motor and worm pulleys [roughly] marked. Firstly to confirm their very slow rotation during normal tracking. The tracking would stop unexpectedly while trying to get Stellarium to work.

Secondly to check for possible cyclic problems causing stalls. There seems to be no obviously recognizable pattern. Pushing the telescope appropriately doesn't always helps to overcome a noisy stall. So it may be localized to the intimate mating of specific worm and wheel "teeth." I have tried LMP grease [ugly] and bicycle oil [invisible] but it doesn't seem to get spread around much. Probably due to the slow and only partial angular rotation of the wormwheels. The majority of slews are well short of an arc from east to west via south.

Early on I tried to polish the very rough teeth of the RA wheel and its eccentric worm. By driving the worm with an electric drill I was able to increase the amount of wear. Though it would still take years before I noticed any real difference using metal polish. The speed of wheel is simply so low even when the worm is driven at such speeds. The worm is likely to wear far more rapidly than the slowly moving [worm]wheel. Each tooth of the wheel sees only a few passes of the worm per hour. While the worm is working hard all of the time. I was able to reduce the RA worm eccentricity but the wheel teeth look no different at all.

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Observatory progress: Remote challenges.

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Wednesday: I added a heavily reinforced padlock and hasp to the main doors as the first line of defense. Alarms, security cameras, remote controlled heavy machine guns and antipersonnel mines will follow in a strict series. Each new level will greet the thieves as they gain a new tread on the stepladder.

I did think of adding a large "scoreboard" to the outside of the building but decided it might encourage suicidal YouTube "chancers." Who were just trying to gain a few more [mouth breathing] followers in the hope of further increasing their  own, obscene sponsorship.

My staged challenges will probably culminate in a [penultimate] brimstone and fire from an eBay flame thrower. And finally, but not least, my "pièce de résistance:" A 10,000 megaton, NK Magnus Opus, "Fat Kim," thermonuclear device. With free, 3 week postage via a Chinese dealer calling himself "Xi" on eBay[UK.]

This final solution would only be triggered should anyone ever reach the observatory floor itself. None of this is probably necessary, of course. Particularly given the mostly DIY and rather amateurish nature of my instrumentation. I just like playing with "my toys.'  😇

Thursday: I was working on a remote [backplate] collimation system for the second folding mirror of the 7" iStar refractor. Only to discover that all my initial efforts were in vain. I was merely pushing the square shanked, coach bolt out of its vital location hole as I applied pressure.

The control rod [tube] was certainly turning with the control knob but there was no change in cell position. I'll have to use a normal, all threaded, machine screw with a clamping nut to lock it firmly in place. Or even a simple cross-pin to stop the bolt from lifting out of its square hole. Some flexibility in the bolt's axis might be beneficial to prevent binding. Then the system should work exactly as planned.

There will eventually be two control 'rods' once I have ironed out the problems with the first. No point in doing it wrong twice before discovering how it really should have been done in the first place. I could have used stepper motors, timing belt drives and Arduino to adjust the mirror cells but I missed that class at school. By about 50 years, if memory serves.

Gave up on the remote, mirror collimation rods after cross-pinning the first as an experiment. Then added a second washer under each butterfly nut and the friction dropped from impossible with stretched fingertips to absolute zero. Now I'm able to adjust the mirror cell easily at arm's length. KISS with bells on! [Keep It Simple Stupid.]

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Mounting: ASCOM-AWR Gotos.

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Monday: Today I had no problem starting ASCOM-AWR from Cartes-du-Ciel. Though it took a while to work out how to tell the software that some blithering idiot had put the telescope on the cradle upside down! It slewed to find Polaris somewhere under the observatory floor! Which was a bit nerve wracking as I sat there [on my shiny, new, observatory chair] wondering it it would ever stop slewing. I find Cartes-du-Ciel too visually complex and rather opaque from a complete and utter lack of practice. i.e. Raw beginner class with only a few minutes under my belt. Here's a couple of videos I made of my earlier attempts at Goto with just the bare stepper motors. [Sorry about the lack of kittens!]







That said, Cartes-du-Ciel does what it says on the 'Telescope' tin. Since it has been kind enough to let me use my Goto drives, as intended, I shall now invest some of my valuable time in climbing the steep learning curve. I'll leave Stellarium on the back burner until I have more practice at Gotos and everything else is working properly. 

I even managed to Set Park on the IH2 handset pointing at Polaris. Which was a first. It usually says "Not Calibrated." Then I wished I hadn't as I walked into both the counterweights AND the OTA as I tidied up for the night. An East-West [horizontal] OTA parking is far safer for bumbling observatory owners, like me. Then there are only the weights to avoid. If I paint them white I may even avoid having to wear my builder's safety helmet! My tinfoil helmet offers too little protection from reality.🙆

Click on any image for an enlargement.

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Mounting: Drive imrovements and folded refractor alignment.

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In my continuing struggle with Slew/Goto motor stalls I removed the RA motor and worm assembly. First I made a brass tension roller in the lathe to replace the brass sleeved, rubber one. Then put the motor back on the mounting. Better, but still occasional motor stalls.

So I took it all off again and withdrew the worm to allow the larger timing pulley to be removed. This is a far easier method than trying to lever the pulley off the worm shaft with the tensioned belt still in place.

A washer was added as a shim behind the pulley and the drive rebuilt and replaced yet again. The motor now ran for much longer before a noisy stall occurred. The OTA and mounting  balance now seems about as good as I can manage. Friction seems adequately low. I'll have to check the height of the worm against the wormwheel again though it seems okay.

There followed an extended session of folded refractor collimation. At first I had the springs fully tightened on the extended mirror cell supports. So I added more packing to the third [fixed but flexible] points of the enlarged triangles. This gave me the freedom to collimate the folding mirrors without compressing the springs so much.

I plan to extend the collimation screws for the second, smaller mirror cell to have adjusters directly on the backplate. The present wing nuts are just beyond comfortable reach. Meaning that I cannot actually look through the open focuser while I collimate. Which greatly slows down collimation. I'll probably use threaded inserts in stainless steel tubes as extenders. I just need to find some smart and comfortable adjusting knobs to go on the backplate.

A visit to a builder's merchant provided a small collection of smart, black plastic furniture 'feet' with potential as collimation adjustment knobs. Matching the threads to a dwindling collection of expansion 'nuts' is proving more difficult. I may be able to turn some hex nuts to fit tightly in the tubing I planned to use. There is also the possibility of cutting fresh threads directly in the tubes [or an adapter] with a tap. Thread locking fluid could be useful here.

Interestingly [?] I discovered that the edges of the OTA frame do not agree with the optical [axis] alignment. It is no wonder I couldn't find Mars by sighting along the frame! I'll have to look into this misalignment because I have no idea why it should be like this. Or whether it is important to image quality. There was an error of about 6' from the optical viewpoint compared with sighting along the corner of the OTA frame when using a 32mm EP. This was using a target at about 175 yards @ 67.5x with a 2160mm focal length.

Click on any image for an enlargement.

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