Flange bearing, plywood equatorial Part 2.

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An update: I just found a 40cm, 16" length of 50mm, 2" stainless steel shafting hidden in my metal stock which appears to be more than adequately robust. Certainly of ample girth when compared with the relatively "flimsy" 31.75mm or 1.25" of the Fullerscopes MkIV when lying alongside. Or the even skinnier 1" shafts of the MkIII. So I have the potential for quite a decent PA axis. Unfortunately it isn't long enough for a Declination axis or I could have used 2" for the Dec and 60mm for the more heavily loaded PA axis.

The best commercial, equatorial mountings use hollow shafts and pre-loaded, opposed, taper [conical] roller bearings. Often with at least some degree of circular "plate" bearing to add extra stiffness. Home made plate bearings are possible but need considerable care to avoid too much friction.

A bit of searching online suggests that steel weighs three times as much as aluminium but aluminium is 1.5x less stiff than steel. So a 2" aluminium shaft would be as stiff as the present 1.25" shafts in steel. While stainless steel is no more stiff than ordinary steel. If I wanted to change 2" steel shafts over to aluminium [for lightness] I'd need to use 75mm or 3" Ø. Unfortunately, there's a bad case of 'swings and roundabouts' going on here. The aluminium shafts would be slightly lighter than steel but the bigger flange bearing housing would be much heavier than the smaller size needed for 2" steel shafts!


An old industrial sized, grinding wheel base offers potential as a sturdy, cast iron, PA axis when mounted on a suitable polar altitude 'wedge.' The 60mm pipe is slightly too large to leave much room for bearing shells. While the original, self aligning, journal ball bearings considerably reduce the potential diameter of the shaft. I thought I might manage to fix slips of Teflon/PTFE between a shaft and casting but it wasn't meant to be. Sadly the dimensions of the casting to not readily lend themselves to a large central wormwheel. By the time I have added bearings I might just as well have used two, modern, pillar block bearings on a hefty support plate.

 A shame because it has the looks [if you have a vivid imagination] of something from the classical, Victorian, telescope making era. More "thinking furiously" is obviously required before I commit to doing anything with it. Turning brass plugs to house journal bearings for the 50mm shaft is doable. My lathe isn't large enough to turn a flange once it is permanently mounted on the shaft. So I'd have to consider practical options for clamping or grub screw fixing of a tight fit. Or go back to the flange bearings and plywood housings idea.

Metals [including stainless steel shafting] are readily available from dealers on eBay[UK] but the international postage inevitably makes a bit of a dent. The nearest scrap yard has lost interest in selling to private customers and is rarely open these days anyway. I had some nice brass stumps in all sorts of sizes from them over the years. Danish metal stockists sell stainless steel, round bars for about the same prices as eBay[UK]. Though not remotely as cheaply as scrap yards. Paying well over £100 [equiv] for a length of 50mm, 2" shafting for a mounting axis just goes completely against the grain. Especially for a hardened scrap yard and flea market re-cycler like myself.

I have discovered a new way of holding the axes of a mounting together. A superb home-made mounting with 2" shafts on Cloudy Nights ATM forum shows the use of multiple taper locking bushes to good effect. These split, taper locking bushes are available in metric or imperial sizes which grip onto a shaft using opposing tapers and grub screws. The tapered bush can hold a sprocket, pulley or drive flange/coupling firmly onto a plain shaft. The bush with flange can be bolted onto a plate to provide a declination axis base for the bearings. The taper can be unlocked by removing the two locking grubscrews and then screwing one of them back into a third hole intended for the purpose. This pushes the taper apart. Finding these bushes are readily available, in many shaft sizes, greatly simplifies the construction of an accurate GEM. Finding the matching flanges seems to be slightly more difficult.

In passing, I noted from the DR NEWS website that Denmark is enjoying 17hours of sunshine at this time of year. It's no wonder it never gets really dark! I usually go to bed around 11pm and look out of the window at a blue sky with Jupiter and Mars hardly making an impression. Not quite Land of the Midnight Sun but close enough, at least for a while, at 55N.

I am presently struggling with my vintage, equatorial mountings and the drives in particular. The worms are constantly rusted and their housing support woeful. I could replace them with a pair of larger Beacon Hill wormwheel sets and matching motors. Though this still leaves me with the limitations of the Fullerscopes mountings. The 7" f/12 is really pushing it beyond its useful capacity. If I ordered wormwheels to fit the MkIV then I could not increase the core diameter later to match a heavier mounting. Concentricity is vitally important in accurate wormwheels. So one can't just turn up a packing bush to match a smaller shaft. Besides which, the clutch is usually a nylon plug in the wormwheel boss. Which would no longer function as intended without an extended adjustment screw passing through the bush.

A Beacon Hill MkII uses 1.5" shafts. An improvement on the Fullerscopes 1.25" but not by much. D&G optical suggest 2" shafts for refractors in the 8" size range. A complete Beacon Hill GEM with 2" shafts and pillar block bearings would weigh a ton and the freight charges to Denmark would have to be considered. Too many options to consider even without the consideration of the likely expense. 

Building a 2" shaft, plywood GEM using Beacon Hill wormwheels would be much cheaper. Even with having to buy the flange bearings, taper bushes and stainless shafts at Danish retail prices. The question is whether it would be as "stiff" as a Beacon Hill mounting in actual use. I have to make a decision because using the MkIV [and MKIII]  is proving extremely frustrating now that I am trying to image the Solar system.

A greater margin of strength would allow me to add finders and subsidiary telescopes and to stop worrying about the weight of it all. I could even balance the telescope properly at half way instead of the usual nose heavy look. If I could have the 7" permanently mounted I could concentrate on imaging the Sun. It requires much less stringent open skies compared to the planets and the Moon. These could be imaged when they present themselves in suitable directions and altitudes. Moreover the neighbours' security lights could be completely ignored for solar imaging purposes. Now I just need to remove the house from the Solar light path without making ourselves homeless. 

Click on any image for an enlargement.

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