This blog has become my ATM design, build and imaging diary. I have recently built several new telescopes, a large equatorial mounting and a raised 10' [3m] dome on an octagonal building. Be aware that I deal with building solar telescopes. Which are potentially VERY dangerous! I can accept NO responsibility for any action not directly supervised by myself. You are NOT entitled to blame any other person for your OWN lack of skill or ignorance. You copy me at your own peril!
The author of these videos has some fascinating content if you delve deeper on YouTube.
Including his restoration of a Merz triplet 90mm f/11 Apo photographic refractor
Easily one of the best amateur astronomy videos I have ever seen! Highly recommended viewing.
An English voice-over is an option with details about Fraunhofer and visit to the Anaformose shop.
Beautifully illustrated and great video content.
Many people like to set new year resolutions for themselves. A challenge, usually involving a difficult change of behaviour or breaking an unhealthy or unwanted habit. It occurred to me that I might have some unique insights into making resolutions regarding amateur astronomy.
The best telescope is the one which gets used. Many amateurs must aspire to a larger instrument. Only to be defeated by the mental and physical hurdles of actually setting it up outside.
For over 50 years I have been building white elephants in the name of ATM [amateur telescope making.] Often my ambitions exceeded all common sense where my absence of clairvoyance really mattered.
I once made a 16" mirror for a large, classical Dobsonian shortly after discovering this class of instrument in American publications. I even went so far as to buy a 20" diameter PVC tube for it. Which weighed at least as much as the full thickness mirror blank! The problem then proved to be a lack of storage height for an F5 colossus of such an aperture! Having perfected the plate glass mirror at F5 I was then forced to regrind and deepen it to F4. A far more difficult and demanding surface.
This also coincided with the arrival of summer and extreme heat in in my concrete roofed, optical workshop. My pitch laps were literally flowing off the tools overnight. I eventually cured the heat problem with a layer of recycled aluminium sheeting. Fixed on top of the cast concrete roof it was highly effective but far too late by then. I never finished that plate glass mirror surface at F4 to my satisfaction.
I found a 24" cast iron lathe faceplate in a scrap yard and dragged it home somehow. This became a disk type, equatorial mounting. A solid steel TV stand acted as the PA axis with 4" steel rollers supporting the rim. Despite ball bearings all round, the whole thing weighed a ton and the friction and momentum was far too high for manual slewing.
I made a 5" F/15 achromatic lens from Schott BK7 and F2. Being so long is was quite a struggle to mount and far too heavy in a 6" PVC drainpipe. So I built a scaffolding pipe tripod and offset and cantilevered, Dobsonian/Berry fork mounting for it. It was never very successful but showed me the planets, Moon and a bright comet. Later I made a rolled aircraft ply tube for it and that transformed its weight. But I was experimenting with plywood, equatorial mountings with Dobsonian PTFE/Teflon bearings at the time. Probably trying to be too clever [again!]
The friction was far too high and the steel pier impossibly heavy to lift out of the ground once filled with concrete. So it stayed put and rocked no matter how I rammed huge stones around the base.
Later on I tried to make an all brass refractor using huge, artillery, shell casings and my home made 5" achromat. These casings quickly proved to be so heavy I could never have lifted the complete OTA. I finally found a 6" steel, spiral ventilation tube for the lens. This was arguably the best tube option at the time but the MkIV mounting still struggled with backlash. Nor was the spiral tube very pretty. I later discovered straight seamed, industrial extractor tubing and have used that on my 7" and 10" telescopes. Provided the seam goes into the gaps for the hinges the plywood packed rings will fit snugly.
I made a 7" f/12 refractor with an iStar achromat lens. This proved to be so long and heavy that my Fullerscopes MkIV mounting could not possibly cope. I had welded up a massive steel pier for the MkIV years earlier but it did not help. Moving the whole thing around on a sloping, undulating and often soggy lawn was an exhausting nightmare! The risk of tipping was very real regardless of which wheels I applied to the radiating legs!
I tried a folded 7" refractor based on an aluminium tubing, shelf building system. That was hardly lighter than the straight tube and only 3/4 as long. Still the MkIV complained.
So then I started on a huge equatorial mounting which would support the refractor and quite possibly my 10" F/8 reflector simultaneously. The latter had proved another white elephant thanks to beam torsional flexure!
This quickly lead to the realization that I had no clear sky views. Just moving the telescope down the rutted, gravel drive to clear southerly skies was nearly impossible. So I decided to build a platform for the mounting to go on top of a raised pier. The pyramidal pier is massive and built from full lengths of 4"x4" x 15' tall!
And so it goes on. A 6" f/12 would have fitted into 2.7m commercial dome. My 7" f/12 is a foot longer than a 6" and has no chance of fitting inside. So I am having to build a 10' plywood dome, from scratch, to go up on the platform. I even looked at a 14' GRP dome intended for rearing calves. But each of the three fiberglass segments weighed 160lbs! I would still go that way if I had clear skies at ground level... but I haven't.
If you find a chain hoist essential to your amateur astronomical pursuits you may well have crossed an important line. My ambition always far exceeds common sense by a considerable margin. Let my example be a warning to those who would imitate me! Though I should admit it has been a fascinating, if occasionally frustrating journey. Almost always done on a shoestring from scrap materials. Success was always going to be dependent on my ability to convert the rather limited raw materials available.
Sunday: I was just lifting the mounting off a reinforced, B&D
workbench with the chain hoist. When the steel strap I hook over the
ceiling joists snapped without warning. A loud crash and the mounting toppled sideways off the bench to lodge horizontally on a stack of
timber off-cuts. So now I had to reach underneath the precariously
balanced mounting to extract the hoist hook from the lifting strop. Which I
had wrapped around the PA assembly for the lift.
Having arranged another
strop above the mounting I could gently lift it clear with the hoist.
That's the second time the mounting has exceeded the limits of
supposedly strong, supporting devices! I have now added a thick plate of
aluminium to the top of an old plastic beer crate to support the
mounting rather nearer the floor.
The
mounting was becoming covered in condensation, from my breath, as I
removed the Dec wormwheel in the unheated workshop. I needed to turn the
brass, spacing collar down a little to center the worm on its wheel. On
a proper wormwheel the "teeth" are cut as indentations with a radius
equal to the worm.
It is obvious that there is only one
possible position where the worm fits intimately in the slanting curves
cut into the wormwheel rim. A smooth cylinder could be made to rotate
in a matching, curved pulley rim but there would be no drive. By adding a
helix to both the worm and wheel rim the worm can drive the wheel,
albeit slowly. Another advantage of closely matching teeth is that the
worm locks the wheel against all free rotation. Any unwanted freedom is called
backlash. This can occur when the drive is reversed during guiding. Or
if there is any imbalance in the instrument on the mounting.
Here
is an excellent series of explicit instructions for making a wormwheel
on a mini lathe. This limits wormwheel diameters to only [about] 7"
maximum diameter. The same as the Fullerscopes MkIV. Those with larger
lathes can obviously make larger wheels. One can save a lot of money
making your own but it does require an awful lot of time and effort to do it correctly:
The image shows the latest arrangement of the Dec stepper motor drive cables.
I decided the short motor cable was far more fragile than the long, sleeved cable connected to the AWR Microstep Drive box.
The initial cable was also rather long. So I folded the motor cable and zip tied it to the edge of the 10mm thick, motor support plate.
Then I P-clipped the heavier connecting cable to act as a strain relief device. This much sturdier cable goes through the large hole in the mounting's fork face plate and thence off to the AWR electronics. AWR were very generous with these connecting cables to allow for a very tall pier for the refractor and/or some distance to the drive electronics.
It is important that no load is placed on the initial, motor cable as the mounting moves the telescope around the sky. So I have added a slack loop to allow for 180° of Declination axis rotation. Not to mention catering for similar PA movements.
I used to park the folded refractor horizontally with the wights up on the north side of the pier. This was only to reduce wind loading on the temporary pier. I doubt I shall have to resort to such "gymnastics" with the telescope housed in its dome.
I don't have a name [yet] for the black, 9 pin, latching plug and socket. The AWR guide mentions a rectangular 'Quickmate' system, but I haven't found any images online to confirm this. I thought I might be able to shorten the first motor cable myself, to tidy things up, if I can source a spare socket. This will save me purchasing a complete, but shorter motor cable from AWR. Though there could be some soldering or crimping of the wires to the pins and sleeves involved. I haven't discovered if the plugs and sockets can be disassembled. Or even re-wired after use without destroying anything. Only six of the 9 pins available are actively used.
Sunday: Dry and 42F: Finally a chance to dismantle the big mounting. I also stripped the stepper motor and worm assemblies and tidied up the motor backing plates. I had left them rectangular and raw after rough shaping. Which prevented the assemblies from being released without withdrawing the axes shafts.
Thanks to fixing the front plate I can now fine adjust the polar altitude angle with the turnbuckle for the first time. The large round aperture in the front plate allows my hand to reach the turnbuckle adjuster. No great effort is required provided I have slackened off the altitude pivot nuts first. I deliberately chose a bulky turnbuckle design to make it easier to turn without tools.
The image shows the PA drive. With 1:2.4 ratio, [14:34] timing pulleys, toothed belt with urethane, jockey pulley, 287t x 11" Ø wormwheel driven by the large, brass, single start worm. The large stepper motor lives in the aluminium box behind the small pulley. The steel flanges on the pulleys are proving rather rust prone. As are the mounting's flange bearings.
Monday is cool but bright. I spent a couple of hours replacing all the worm assembly fixings with stainless steel, hex socket head screws. Added stainless steel spring washers beneath all the nuts to avoid them loosening with motor vibration.
The worm assemblies feel very solid and secure. While [hopefully] looking quite 'tidy' thanks to the sturdy 10mm sections of aluminium plate and the square al. tubing, stepper motor housings. My usual 'belt and braces' approach helps to ensure rigidity. I still have to smooth the edges of the newly cut motor plates. A bench, disk sander would have been handy but an expensive investment for a decent one. Not sure how to apply worm mesh, fine adjustment yet.
The single, tiny grub screw on the Beacon Hill, Declination worm housing could not hold the journal bearing in place. So I drilled the housing close to the bearing. Then added two screws with washers both sides and doubled lock nuts for security. The bearing can no longer work its way steadily outwards during slews. Over-tightening the grub screw merely locked the ball bearing solid so that it could not rotate. Beacon Hill was very mean with the worm shaft overhangs.
The Declination drive, stepper motor is visible just below in its box section housing. It was sheer luck that I found the square tubing at the scrap yard just when I needed it. The clearance between the motor and housing is ideal. The height of the square tubing is also perfect for presenting the worm to the wormwheel.
Wednesday, 45F, mild, dark and windy with showers. Spent a couple of hours in the workshop balancing and testing the mounting and AWR drives. Before balancing, the RA motor was apt to complain about having to work 'uphill.' I also fastened off the stepper motor cables with zip ties to provide some strain relief. The Dec motor cable will need to be 'dressed' to allow rotation without tension. This should not be too much of a problem because the telescope(s) would be upside down if allowed completely free reign.
I have photographed and printed off the AWR IH2 menu in several sizes to have reminders of the cascaded steps required. Having not used the drive system for months I had forgotten much of it. When I finally have the observatory set up properly I shall be pointing to objects for Goto slews on the computer screen.
Thursday and Friday: Testing drive slews with the AWR IH2 handset.
With the mounting raised on a bench the sheer scale and mass of it is quite overwhelming. The buzzes occur when starting and stopping the motors. I wasn't sure whether to shim the motors for better conduction or leave them more fully exposed to the air. I ought to have used a more neutral background for the video but had no other, lightweight tarpaulins left to quickly hide the workshop clutter. White always confuses the camera. PS: I have invested in sheet of neutral grey cloth for pocket change at a charity/thrift shop.
Dressing the divided, stepper motor, drive cables is proving slightly awkward. Both cables presently exit the access hole provided for PA altitude adjustment. The RA cable need only be quite short but the Declination cable must not hinder rotation of the PA over a rather large circle.
I have already managed to stall the drive during slews when I allowed the Dec cable to become tight. With only short, primary motor cables, from AWR, this places a rather large plug and socket dangling in mid air not far from the motor.
Unable to obtain them locally, I have ordered a boxed assortment of Nylon P-clips online. This will improve my chances of sorting out the cable problem neatly. There is no need for the main cables to be readily removable because the mounting will be permanently installed on the pier. So the heavier, main sections of cable can be clipped neatly onto the mounting. With plugs easily removable from the drive boxes at the far end when desired.
