3D Printed Fork Mount and Micro Dome Observatory?

[Gina]

I wonder if this is possible   I thinking of a widefield imaging rig using vintage SLR film camera lenses.  I'm thinking fork mount as it's more compact than a GEM.  The geometry and design engineering of this should be a nice brain taxing exercise for me and I love a good challenge - I have several in progress already   I have already built a larger than average 3D printer with 300mm cube printing volume and slowly working on a Giant printer with a build volume of 750mm square by 400mm high.

I have already printed a turret style mounting for a triple widefield imaging rig in PLA but this was designed for a GEM - NEQ6 or EQ8, and will want changing for a fork mount.  I plan to use PLA for the fork mount for its rigidity.

For the dome, which will be subject to everything the UK weather can chuck at it, is another matter.  PLA is unsuitable and I have read that ABS doesn't likr the UV in sunlight so maybe Nylon but I can't seem to find UV info on this yet.  I'm thinking dome rather than some sort of opening roof as it provldes more protection and can be smaller - it will house just the mount and imaging rig plus motors and control electronics which will be cabled to my warm room nearby.

[Gina]

PA6 is available at about £20 a Kg reel so costs more that ABS or PLA from cheaper sources but I've read this, which looks promising :-

The UV stability of PA6 is better than that of most other engineering polymers.

[laser_jock99]

Interesting projects. I can't comment on the type of plastics to best use but in my experience most don't like UV.

[Gina]

Yes, so I've read.  One problem with PA/nylon seems to be its absorption of water with makes it softer and reduces glass temperature.  So hot sunshine following rain would probalbly not be good.  I think I would prefer to go with ABS, which doesn't absorb water and can be obtained in more colours than black, white and natural.  eg. a nice dark green would make the dome almost invisible from afar.  ABS has many other useful properties such as easy cleanup and solvent weldable using acteone, making multi-part assemblies easier that using nuts & bolts.  Items I have already made of ABS and used outdoors haven't shown any signs of deterioration as yet

[Horwig]

Knew you would be converted to fork mounts eventually Gina, welcome to the dark side

Would something like this be doable on a 3D printer?

http://vega-sky-center.com/images/A-Completed_SAO_10-inch_Newtonian_01-20-2007.jpg

Huw

[Davey-T]

All large scopes are fork or horse shoe mounted, theoretically a much better system than GEM mounts, and you can also get nice big worm gear wheels or friction drives (probably easier to implement for DIY)

Heard a rumour that one of the big mount manufacturers are working on an adjustable width fork mount.

Dave

[Horwig]

Heard a rumour that one of the big mount manufacturers are working on an adjustable width fork mount.

Dave

That might be this from Gemini:

http://www.geminitelescope.com/mofod-mkii-fork-friction-mount/

Huw

[Davey-T]

There you go Gina, copy that 

Dave

[Zakalwe]

All large scopes are fork or horse shoe mounted, theoretically a much better system than GEM mounts, and you can also get nice big worm gear wheels or friction drives (probably easier to implement for DIY)

Heard a rumour that one of the big mount manufacturers are working on an adjustable width fork mount.

Dave

Paramount has just released this:

http://www.bisque.com/sc/pages/ParamountTaurus.aspx

[Horwig]

Oh that is a monster, Gina, beat that 

H

[Gina]

Knew you would be converted to fork mounts eventually Gina, welcome to the dark side

Would something like this be doable on a 3D printer?

http://vega-sky-center.com/images/A-Completed_SAO_10-inch_Newtonian_01-20-2007.jpg

Huw

Yes, I would have thought so

[Gina]

Oh that is a monster, Gina, beat that 

H

Very interesting but ATM I'm just aiming at something for my widefield rig

[Gina]

I'm not planning to use worm gears - I have a previous design using timing belts and pulleys but my experience with 3D printers has led me to prefer cords and drums (and/or maybe  large spur gears and pinions) with Nema 17 stepper motors.  I can use A4988 stepper drivers with 16x microstepping and probably drive them from an Arduino - my "comfort zone"   I can already print up to 280mm diameter and when I get the Giant printer built I shall be able to go up to something like 740mm but I won't need that size for the mount - maybe not even for the dome.

[Gina]

I've found my previous thread on building a mount :- Ideas for a Home Made Mount for my WF Triple Imaging Rig

[Gina]

The widefield triple imaging rig consists of a turret containing the three sets of lens with extension tubes, filter holder and astro camera.  Using 105mm FL lenses, these units are 230mm long.  They will be mounted in a turret in a triangular arrangement with guidescope in the middle.  The turret will be about 200mm diameter and mounted in a framework/box with mounting points for a fork mount near the centre of gravity.  I would imagine the width being something like 250mm between fork mounting points.  The drive wheel for DEC could be integral with the turret box/framework.  Having a mount designed specifically for a particular imaging system has several advantages.

With Asahi Takumar 105mm f2.8 lenses and Atik 460EX cameras the C of G is around 130mm from the end of the camera so a clearance of something like 150mm to 200mm will be required in the fork.  I think I'm getting near constructing a model in SketchUp   I need that before I can gauge the size of dome required.

Coming to the dome, I had considered using a globe centred on the mid point between fork mountings with shuttered slot to "see out of" but I'm now thinging this will be too complicated and a regular alt-azimuth dome may be more realistic.  I have some ideas for driving the dome and shutter which are rather different from the full-size dome systems.

I think I may design and print a scale model of the final rig, mount amd dome to test the principle.

[Physopto]

Hi Gina,

 I would be very careful with this one. Plastic deforms under load (it usually will not recover, hence the term plastic deformation used to describe permanent deformation in steels and alloys). It has very approximately has an expansion ratio about 4 times that of steel. This could cause all sorts of alignment problems.

Derek

[Gina]

Yes, I am aware of this and wouldn't consider it for anything other than a widefield rig.  I'm hoping active guiding will compensate for some of the errors but I'm quite prepared for problems - it might simply not work,. hence the question mark on the thread title.

[Physopto]

Well I wish you lots of luck Gina.

Derek

[Gina]

Thank you Derek

[Robp]

Would it not be possible to seal the plastic to block the water and UV?

[Gina]

Would it not be possible to seal the plastic to block the water and UV?

ABS will take paint well I've read but not nylon.  I've gone off nylon anyway - too flexible particularly when damp/wet.  I'm thinking of PLA for the mount and ABS for the dome.

[Astroscot2]

Gina, what happened to your mini observatory that you constructed for your wide field rig, I was looking forward to seeing that in action .

[Gina]

I still have it but haven't done anything to it for some time.  Not entirely abandoned, in fact I may well get that going first.  The printed fork mount and dome is more of just an idea ATM which may not be practical - the current widefield NB triple imaging rig is pretty heavy and I think a plastic mount may struggle with it.  This thread is mainly to think out ideas and open the subject for discussion.  I have been thinking again about using a modified DSLR for widefield astro imaging - that would save a lot of weight even with Peltier TEC cooling added.

[Gina]

Investigations of 3D printed domes/clamshells of various sorts proved to be too difficult so its back to aluminium and wood.  Also, decided plastic was too inclined to creep to use for the mount and that will be made of aluminium too.