Rusted

Yes, it would make good sense to triangulate the open, Beacon Hill style frame as you have done. A prism frame has no stability across the uprights unless it is triangulated by reinforcing plates on all three, square faces. [Stressed skin effect.] The problem with most mountings is that the manufacturer has to allow for almost universal, PA altitude adjustment. Which means that some (obscenely expensive) high end mountings abuse simple, blade-like, PA, support forks. Because I had no interest in lightweight mobility I used a PA support fork in 20mm solid metal. But, further, ensured the fork tines were braced upright by clamping across the massive, square section, PA housing. This was only possible by offsetting the PA altitude, clamping stud to clear the PA shaft. The Fullerscopes MkIV shot itself in both [fork] legs by insisting on a centrally placed, PA, altitude pivot. [Cosmetic handicapping!] Which meant undersized, screw threads in the very soft, cast metal, PA cone. This denied the application of a massive clamping force via a long, through stud. These silly screw threads are probably all as badly stripped as the silly, little, altitude locking screws by now. The only way a MkIV [and many other mountings] makes any sense is with an altitude adjustment turnbuckle. I considered drilling a large hole in the underside of the MkIV's PA casting. To allow the insertion of large [hex socket] PA altitude bolts to face outwards through the fork tines. "Fishing" such bolts through such an arrangement would be a nightmare. So I did not proceed. The MkIV's PA fork "ears" are weak metal and hollow section to boot. So easily crushed unless stuffed with packing washers. I should say that I am grateful to the MkIV for teaching me to avoid all of its serious pitfalls as I designed my own mounting in my head. Parallel reinforcement by multi-tasking every component proved to be the way ahead at lowest cost. Where I could not afford castings and very large, box section profiles, I used multiple compression studs in all 3 planes. Each component leans on all the others to become greater than the sum of their parts. Unfortunately I abandoned my own principles when it came to supporting the [now glaringly inadequate] Beacon Hill, worm housings. I badly underestimated the linear and torque loading involved on the motor/worm housing. Made worse by the large cut-outs in the motor box sections. To allow the drive motor power sockets to clear the box during insertion. "Cosmetic handicapping" is the fine art of making something look pretty, for its own sake, even if completely fails to function mechanically.

Just a few thoughts: Domes are great! Instant gratification for observing/imaging and instant cover when a passing shower arrives. The rollers of my [raised] home made, plywood dome rest on heavy timbers and there are plywood obs. walls. The floor is high quality, larch planking and is deliberately spaced for ventilation. The gaps between the observatory floor joists are open to the outside air to maximise ventilation. Thermal mass must be very low but still averages 3-5F offset. This is the difference between the outside air temperature [in deep shade] and inside the dome. An indoor/outdoor digital thermometer allows easy monitoring at low cost. A concrete pad would and should be shaded from direct sunshine by the obsy. itself. The pad's high thermal mass would act as a thermal flywheel. Probably helping to even out the observatory's internal temperatures. Careful sealing around the edges of a GRP dome will prevent wind blown, water ingress. A covering of insulating foam panels over concrete sounds ideal. Though I have never tried them. BTW: There are waterproof wood product sheets available in metric 8'x4'. A "wooden" floor doesn't have to be softwood or terrace boarding. Man-made terrace boarding is also available. An alternative to a complete concrete pad would be individual, cast concrete, pyramidal, carport anchors. I used eight of these for my two storey building. Four more for the isolated timber pier. This avoided the very serious problem of a massive concrete pad to be rid of on moving house! My own ground floor is pea gravel over self-compacting gravel. I added concrete slabs for the foot trafficked areas to avoid the gravel dust being carried upstairs. Artificial lawn might make an amusing "alternative" floor covering for an observatory.

How about simple bracing between the base and the worm assembly? Go kart track rods with built in turnbuckles and spherical joints? If it still needs such stiffening?

Update: Today I slid a 3' length of 50mm bore, metal pipe over the extended lower end of the PA shaft. There was no detectable play in the PA flange bearings despite my best efforts at leverage in all directions. Suggesting only the illusion of lateral PA movement when the 6" telescope was used as a lever in the video. I'm still doodling potential motor/worm mounting ideas to include the clever "flexor" hinges. I need these "hinges" to be much nearer the worm housing and further away from the motor housing. The belt drive can easily manage the tiny movements required for the worm to maintain mesh. New, longer belts are readily available, if needed. The box profile, motor housing is an ideal support for the worm, for height, but only in the cosmetic sense. The heavily cutaway, box profile seems to badly lack rigidity. So, ideally, the worm housing should be treated as a separate, hinged unit. Or, the hefty, stepper motor could be tightly packed around, with suitable shims. To make the motor into a structural element of the box profile, worm support.

Thanks Huw. I'm studying my options.

Thank you Huw. Sorry I didn't answer yesterday. I am unwell. I'll be back.

Thank you both. I have made roller bearing, disk mounts up to 24" diameter but never motor driven. Using AWR drives I cannot manually move the mounting. Motor drive only. Not quite the same thing, but I added a 7" [180mm] diameter, thick disk at the top of the PA to spread the loads into the Dec housing. The Tollok bush expands into it for improved stiffness. The disk mounting has the problem of securely attaching the Dec axis housing unless the disk is made very large. Thanks Huw. Similar arrangement to a precision clock, pendulum suspension. I'll have a dig in my scrap, phosphor bronze collection.

Some progress: After hours of searching very unhelpful bearing websites I found some angular contact bearings in the matching size to the original deep groove. 12x28x8mm for a straight swap. Whoever produces these bearing websites needs a course in customer satisfaction. Endlessly random size listing and filters which completely ignore entries. Nothing in Denmark that I could find. Had to buy them from the UK. Delivery by snail mail. https://simplybearings.co.uk/shop/p88002/Budget-7001-Single-Row-Angular-Contact-Open-Ball-Bearing-12x28x8mm/product_info.html

Hej Lars, I have had the same problem with translating old Danish [technical] catalogues and manuals to English. Miserable weather here. Grey and overcast. Rain is promised for this afternoon.

Hej Lars, If the original Swedish text is available online then Google Translate may be able to do the rest. Right click> Translate this page> Auto/English. These old and deserted observatories have a rather melancholy [sad] atmosphere. Still fascinating though and thanks for sharing your visits with us.

Thank you Huw. Sadly I have no recollection of your thread. My failing memory must be even worse than I feared. You seem to have been struggling with your Beacon Hill parts in a parallel universe to my own. Your approach is far more sophisticated than my own. I have never tried PHD. Only now am I considering screw adjustment of worm/wheel mesh. I usually adjust by feel alone. Angular contact bearings, of identical dimensions o the originals, would/might reduce end play. More importantly, without altering the original dimensions of the channel section worm "housing." There are NO taper roller bearings available in the 12mm bore x 28mm outside dimensions. Even ignoring the width. There is a very severe clearance constraint before the worm drive pulleys jam in the wheel teeth. Or, the wheel rubs on the opposite end of the [channel section] worm "housing." Already much filing required. Which means increasing overall bearing dimensions would require that they be moved outboard of the present simple channel. Which is physically impossible within the present limits on worm shaft length. There is hardly enough room for a pulley to grip. Fitting outboard bearings to supplement the originals is also impossible for the same reasons given above. I am using triple grub screws at 120° on all my timing pulleys. It was the only way of keeping them on. I edge drilled the support metalwork to allow a long section hex key to reach the hidden grub screws. My brass worms are presumably bonded to the steel shaft with something like Loctite. Or even shrunk on? I could remove the worms and turn more generous shafts to fit larger, more widely separated bearings. Possible risk of even worse eccentricity? Could I alter/spoil the metallurgy of the brass worms if I heat them? I have searched for "flexors" but came up empty. Is this a generic term for a flat, blade spring?

Okay. After a whole morning of dismantling, rebuilding and fiddling I have two more videos. I used a temporary fibre washer to take up the end play. Just as a proof of effort expended. I'd need the lathe to make a new stainless steel washer. No desire to stand at the lathe at 36F with my nose dripping. Watch later

Thanks and correct on all counts. Getting the exact angle I need for the camera is quite difficult. The wheel obscures the view from each end. I'm using a video tripod with rise and fall head and a short zoom lens to be able to frame the view exactly. Fitting the angle profile, on the left of the worm housing, has denied the spacer washer its former seat. Plus the four outer retention washers are no longer functioning. I'll be back with another video later. First I have to sort out the ridiculous end play in the worm. Then [hopefully] the inherent flexure in the worm housing can be properly seen in isolation.

Solar, southern hemisphere activity taken to the extreme?

Not so much "high pushrod" as no pushrods at all.

I was rather surprised at the [claimed] carrying capacity/price ratio of the larger Fornax mountings: 102 & 152. Sadly, the problem of carrying long and heavy refractors [even doubled up] still remains a complete unknown. Very little appears online about Fornax mountings. Most of it is just parroting the standard, sales patter. Very little discussion about them on here, either. Most posters were pointing at alternatives or simply changing the subject. These mountings are available, usually with a modest waiting period, from some of the popular, online dealers. Does anybody here actually own one of the bigger Fornax GEMs and is willing share their first hand experience? Possibly by PM? Please don't start suggesting alternatives because they hold absolutely NO interest for a big, heavy refractor, high res. imaging fan on a budget. I am really only interested in hearing rumours and hands-on tales about the "Fornax 100 & 150." [Later 102 and 152] Thanks for your time.

Whoops! Well spotted! I dismantled the whole drive assembly the other day and missed the washer which takes out the end shake on the worm.

And a second video from below confirms the worm bearings are not being restrained.

Okay. A quick video showing the general looseness of the RA wormwheel/motor housing. Not only is there obvious end play in the worm bearings but the housing itself is flexing.

I checked the free play in the PA axis using the same dial gauge set-up as the eccentricity test. The telescope was pointed to the Pole with the weights down on the north side of the pier. Despite pressing up and down on the Dec counterweights, with my hands, I could only manage a change of 0.02mm in the dial gauge reading. I considered that a trivial deflection. I could preload the PA flange bearings but it seems unnecessary. The upper, flange bearing carries the considerable load while the lower one merely aligns the heavy 50mm shaft. The self-aligning, flange bearing's, load capacity easily dwarfs any puny loads I may apply manually or via the telescopes. The large and heavy bearing's close fit on the 50mm, stainless steel shafts is excellent. The whole PA motor housing can be seen to physically flex in line with the worm when the telescope is used as a long lever to rock the wormwheel in RA with the clutches locked as usual. Today is misty and cloudy. So I shall attempt to video this flexure while I cannot image the sun. The stepper motors are a close fit in their box profile housings. Which limits fixing screws to Csk heads. Countersinking the holes for the screw heads inside the narrow box sections required some ingenuity. The limited wall thickness of the box profile severely limits the choice of screw fixing size. I could wrap sections of 75mm, angle profile, around the motor boxes for increased stiffness. Then bolt these to the main supporting plates. Though the clearances are very tight. My main worry is that motor housing flexure alters the engagement of the worm with its wheel. This should only occur during ramping up to slewing speed. However, the telescopes must constantly apply dynamic loads during guiding and under wind loading. Touching the telescopes produces severe shaking of the image at typical solar and lunar magnifications. Which is why I originally applied electric motor focusing. I must be rid of this shaking to broaden the wind conditions under which I can safely image.

I too have been suffering from thermal wobbling, simmering, boiling and drifting in and out of focus. The moon yesterday evening had what looked like a fierce torrent of running water crossing it. Mars was even worse despite bing higher. It was hopeless trying to image in that. The diagram shows the brightly coloured bits [technical term] passing over Denmark. So we copped the leftovers of whatever Gravely didn't need.

Unless you focus slowly you may well have passed the sharp focus point. 47-50x is quite a big disk. Remember that the filter has no real effect on the focus point. So the telescope should focus exactly where everything else does. Stars & planets, etc. Even a distant tree should be somewhere near the focus point or usually just outside of it. The moon will be at the same focus point too if it is available. Presently East in the early evening and rising high to the south. You can't miss it. I sometimes use a pencil mark on silvery drawtubes to save fiddling about. A narrow magic marker would do if a pencil mark won't show up on chrome.

Thanks. I released the worm housing and measured the 11" RA wormwheel eccentricity today. Maximum variation was only 0.02mm on the rim beside the teeth. I left the telescopes in place and measured in two x 180 degree arcs. Without any end loading on the flange bearings I was able to flex the PA by a similar amount. There doesn't seem to be much to worry about given these numbers. The most obvious problem is that the RA worm housing flexing when I manually rock the telescopes in RA. I used 70mm square tubing with a 5mm wall thickness [from memory.] I was able to see the flexure without needing any aids.

Just to complete the thread: I finally have the MW 12V 12.5A PSU safely housed in an inverted, snap-on lid, food container. Part of a nested set from the supermarket at a ridiculously cheap price: Once closed, the white lid/base is so difficult to remove it needs tools! A 40MM cooling fan keeps an airflow going over the unit inside the box. Ventilation holes were drilled in the lid/base at the far end from the terminals for safety. I intend to fit some rubber feet and hang the unit off the pier. A compact "marine" fusebox uses blade-type fuses to protect the kit. The airflow has reached only 63F inside the box after running for several hours. Thanks to all who responded with advice and entertainment.

Bothered by constant thin cloud across the sun. WL rotated and cropped to orientate correctly. Well worth a peek in WL. AR2786 is big and has a nice halo. Difficult to choose an H-a because they were all a bit soft. The light bridge across AR2786 is forked but difficult to see in my images.