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DIY Fork Mount for Widefield Imaging Rig


Gina

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Just think of all those over engineered Victorian edifices that would have disappeared long ago if they'd been designed on computers using the least amount of materials to save money.

Dave

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36 minutes ago, Davey-T said:

Nowt wrong with a bit of over engineering :grin:

Dave

No, probably not :D

The bearing ID doesn't quite match the pipe I have but I can pad out the 1" OD pipe to fit.

Edited by Gina
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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.

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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.

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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.

Edited by Gina
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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!!!

  1. DIY Fork Mount.
  2. Dome micro observatory.
  3. Improve my GinaRep Titan 3D printer.
  4. Main observatory remote roof control.
  5. Grandfather clock.
  6. Epicyclic clock.
  7. Mini observatory for NEQ6 and Esprit telescope (proposed but not confirmed).
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I think CNC machines are a bit like 3D printers, my son in law bought one and its first job was to make more substantial components for itself :grin:

Programing is fun though

Dave

Edited by Davey-T
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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.

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

59083950509f1_BigBallBearingPlate01.thumb.JPG.f43b310c8bed619d69ca329fb9a82442.JPG

Edited by Gina
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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.

5908a47410992_MountFramework01.png.15dea12241b7673071d4b2f02eb67a0d.png

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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.

5908aa993dc5f_MountFramework02.png.ceb9843d6838858e4c0a38c93408d821.png

Edited by Gina
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I actually have three jobs in progress at this time :D   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.

5908b64dcd3ec_MountFramework03.png.83e35d24c91b73c4d9a46eb93143fd0a.png

Edited by Gina
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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.

5908c6fb1f3d4_DomeMount03.png.8a79de83130f7ef85147cd28b131862b.png

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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.

5908cfdfb7aca_DomeMount04.png.c9592d4bc7c0a9687dbbb61a13ce488c.png

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57 minutes ago, Gina said:

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.

 

Have a look at the picture of my mount above, the bottom end of the polar axis plate is fixed to the base with a dirty great big hinge, I'm taking no credit for that, it started life as a Beacon Hill mount.

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Why is the view upwards a problem ? All our domes need slot clearance overhead. You will face larger problems with sideways wheel forces for dome rotation and bearings gravitating downward to the lower end of the track. 

Alternatively you might think about making it all alt-az and using a field rotator.

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2 hours ago, skybadger said:

Why is the view upwards a problem ? All our domes need slot clearance overhead. You will face larger problems with sideways wheel forces for dome rotation and bearings gravitating downward to the lower end of the track. 

Alternatively you might think about making it all alt-az and using a field rotator.

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.

Edited by Gina
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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 :D

I've pretty much sussed out the mounting but yet to decide on the fork though aluminium seems favourite.

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1 hour ago, Gina said:

I've pretty much sussed out the mounting but yet to decide on the fork though aluminium seems favourite.

Did I mention that I get all my aluminium from Forward Metals, very good, quick, reliable service, they even answer the phone :grin:

Dave

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