Gina

I think I've used them myself via ebay. Found two more pieces of aluminium both 200mm square, one 4mm and one 3mm thick.

I have decided on an equatorial fork mount for my widefield imaging rig and to err on the side of over-engineering. The imaging rig is not a lightweight DSLR with plastic lens - the lenses are real glass and metal and the camera a full blown astro model - neither are light and then there's filter wheel and stepper motors and various mountings. Not really surprising it weighs 3Kg - 6x the weight of a DSLR I've pretty much sussed out the mounting but yet to decide on the fork though aluminium seems favourite.

Same here. I too like trying unconventional ideas and also some of these fail but it's this sort of attitude that leads to advances in science and engineering Good luck with your second build

This is not a conventional dome but based on the SkyShed Pod using two hemispheres rotating on a vertical axis. But I'm beginning to wonder if the benefits of this arrangement are as much as first thought. I may yet go back to a conventional dome with slot and sliding shutter. OTOH with the light weight of 3D printed object I don't thing the sideways force would be a problem. I hadn't thought of using alt-az as I have never used it and heard it gave rise to all sorts of problems. The imaging rig has a field rotator but it's only crude and designed to be set for good framing and left fixed while imaging. An equatorial mount, if properly PA adjusted, should only need RA motion.

Ah yes, good idea - thanks

Been doing a bit of "lateral thinking" regarding getting a vertical view without the dome stopping it. If the dome rotation axis were changed from horizontal slightly towards the polar axis the view upwards could be cleared. The problem would be reduction of view towards the horizontal to the south. However, this could be cured by extending the rotating parts downwards a bit.

The design above is flawed - there would be an upward force on the lower bearing and thus the plate attached to it. The front plate needs to be attached as far up as possible to reduce stresses and could be vertical. 200mm is not long enough so if I don't find something suitable I'll buy it.

I might pour a concrete block - haven't decided yet.

I actually have three jobs in progress at this time The fork mount, the dome and sorting out my stuff all of which are proceeding rather nicely I have found another sheet of aluminium - 300mm x 200mm x 4mm. I think this might be thick enough to take an adjuster screw for the PA altitude adjustment. On second thoughts, the screw thread doesn't have to be in that plate, it can be in the strip above or in the base plate.

Found another piece of aluminium, rather thin but I think it should work on top of the big lump to use to adjust the azimuth. It's 400mm x 200mm x 3mm. That just leaves something to adjust the altitude. Were it thicker I could thread it and use a screw adjustment. I'm still sorting through my store room and might find more aluminium.

I've dug out some more aluminium - from my now defunct 400mm triple imaging rig. There are two pieces 200mm x 150mm x 4mm and one piece 500mm x 250mm x 10mm. One of the smaller pieces would make a triangular support arrangement and I might use the big piece for the base.

I have found a 10mm thick piece of aluminium wide enough to take the bearings and about 280mm long. That's a start

CNC machines are very like 3D printers except that they have 3 variables rather than 4 (unless you control the cutter speed and then they compare even more). CNC machines need much more solid engineering than 3D printers though.

I can't afford to buy one but I am considering making one but probably for wood rather than metal. Won't be starting that project for some time though - I have several other projects to do before that and I need to get my workshop cleared out and benches installed. I do have a mini-mill for small items - I could take the head off that for the CNC machine for metal working. No, no, no I am NOT starting a CNC machine yet!!! DIY Fork Mount. Dome micro observatory. Improve my GinaRep Titan 3D printer. Main observatory remote roof control. Grandfather clock. Epicyclic clock. Mini observatory for NEQ6 and Esprit telescope (proposed but not confirmed).

Very interesting Dave I look forward to seeing your build It's similar in many ways to my Titan printer but more heavily engineered and with more Z capacity (375mm v 330mm). You will need a bigger fume cabinet than mine to cater for the extra height and the loop of filament feed tube. The heavier engineering may make yours more accurate but I still have work to do on mine so can't say yet just how accurate it is. I'm hoping to get back to mine soon. I'm lucky in having plenty of space so will be retaining two working 3D printers - I have retired my little Up Plus 2.

I'm wondering about using wood (probably plywood) for the fork or I might stick with aluminium. Anyone any thoughts on this? I would rather work with wood than metal.

I'll add a bracket to one of the forks for my PoleMaster camera for polar aligning unless I devise some other method but that might be difficult with a wide angle camera system. The PoleMaster works very well and doesn't need accurate alignment with the polar axis to work successfully (unlike a polar telescope). Of course, to use this method needs Polaris visible from the observatory position which limits where I can put it.

I have some 12mm marine ply left over from the cylindrical (clamshell) mini obsy build that I could use to make a supporting structure. In fact I don't see why I shouldn't use that for more of the structure. I see a number of wooden piers in use.

No, probably not The bearing ID doesn't quite match the pipe I have but I can pad out the 1" OD pipe to fit.

I have a pair of very large pillow block ball bearings which I bought for the fold-down flap on my observatory but changed to some lighter weight stainless steel cased bearings. I get the impression that to use these for the fork mount would be like "using a sledgehammer to crack a nut" but I wonder. I have these and no current use for them and they fit some aluminium pipe I have.

Hmm... Taking drives and supports together doesn't seem to give the answers. I think I'm coming back to 3D printing with extra support. Anyway, 3D printing makes for easy design and could act as a test setup to prove the geometry. I'm thinking of ball bearings for the RA axis and ball bearings would be easiest for the DEC axis as well. The widefield imaging rig weighs just under 3Kg including an 11" ADM dovetail bar which would probably not be used with a fork mount. This 3Kg will be overhung on the main RA bearings by 200mm from the top bearing. If the RA bearings were spaced by 200mm the top bearing would be supporting 6Kg due to the leverage plus the weight of the forks etc. The spacing shown in the diagram above is 140mm but can be increased fairly readily. This is making me think of quite large bearings.

Been trying to work out all the drives and their motors as well as the mounting hardware and most seems to indicate an aluminium structure. Maybe with 3D printed parts as well but... This diagram shows the RA axis drive, plus the altitude and azimuth geometry. The DEC drive would be on the fork.

Here's a cross-section diagram of the mount, imaging rig and dome enclosure/observatory. Just the basic geometry drawn to scale without drive motors and belts etc. The dome shown is 600mm diameter and more than big enough.

In fact a design produced for 3D printing is a good way to see how things fit together.

That's a good thought, I'll look into it