Mountings and Controls For Widefield Imaging Rig

[Gina]

Having the dovetail bar I have been able to design the attachment of the rings that take the rotation running wheels.  Now printing the thinner one - it's a close fit on the print bed of my Pilot printer but should be alright.  Here are models of the rings and a screenshot of the thinner one in the Repetier Host 3D printing software.  Printing time about 2 hours.

[Gina]

Printing has started off alright

[Gina]

Designed the focus gears for the 105mm lens.

 

[Gina]

Print finished and released from the bed.  It's alright - just a bit of lifting where the print was close to the edge of the print bed.  Not enough to detract much from its strength and plenty of area to solvent weld to the other part when I print it.  Probably overnight as I expect it to take five or six hours.  Meanwhile I'm going to print the 105mm focus gears.

Seems my print bed heater doesn't get right out to the edge - maybe I'll add a sheet of aluminium to conduct and spread the heat.  It will add to the thermal inertial though.  Alternatively, I could up the bed temperature for these larger prints.  I'll try that for the other big one.

[Gina]

105mm lens focus gears printed perfectly and installed on lens and motor shaft.

[Gina]

The thicker running wheel ring is ready to print - 2hr 40m and 21m of filament.  Thats much quicker than I thought   So I'm printing it now - probably be done by the time I go to bed.  I have increased bed temperature to 120C (from 100C).  Getting there

[Gina]

That should take care of the objective end of the rotation rig, next will be the camera end.  That is not just a bracket but stepper motor with pinion to engage the big gear on the camera end of the rig.  For the moment I will assume the little 28BYJ-48 geared stepper motor will be adequate as they are quite strong and the rig shouldn't take much torque to turn it.  The latter may depend on arranging the wiring such that it doesn't impede rotation.

In the worst case I have a NEMA17 with 100:1 gearbox which could drive the turret directly with enough torque to break the plastic!  I know that because I have used it on a large 3D printer for the Z axis drive and broken more than one pulley when the electronics went wrong and the drive didn't stop at the end of travel.

[Gina]

The drive gear for the rotation rig has 70 teeth at mod 2 and I have designed a stepper motor pinion with 14 teeth.  This gives a gear ratio of 5:1 and estimated rotation time from one end to the other (180 degrees) of 25s.  I think this should be a reasonable compromise between patience and power.

[Gina]

Print of the wheel ring failed due to curling of already printed filament catching on nozzle and impeding the motion causing the stepper motors to miss steps.  Maybe this is just a little bit too big for this printer...

Well I have been thinking of giving my "GinaRep Titan" 3D printer the going over I have just given the Pilot printer.  The Titan is half as big again in each dimension.  Print bed is 300mm square and printing height 350mm.  I currently have a 0.8mm nozzle on it as the working one but it has a dual hotend and I can use a bigger or smaller for the other if I like.  It uses 3mm filament as opposed to 1.75mm.

[Gina]

I want to test out this rig ASAP so I've chopped some bits off the model and going to try printing that now.

[Gina]

On layer 3 and looking alright so far   I'm not staying up to see it finish - it will either be alright or it won't - I'll find out tomorrow.

Meanwhile, I've downloaded the latest Repetier Host and Cura engine for slicing, installed on my Win 7 desktop and set them up ready for testing the Titan printer tomorrow.  I'm not grovelling about behind equipment to plug in tonight

[Gina]

Printing fine still and several mm thick so far    Good night all

[johnfosteruk]

This is a cracker Gina, will you be taking orders?

Seriously, I'm looking forward to the first images produced on this rig.

[Gina]

Thanks John

The overnight print went fine and the two parts fit together perfectly.  I need to model and print the missing bottom bit but may not bother with the other bits I cut off the model.  It seems very strong and rigid as it is but the proof will be under load.

[Gina]

Parts assembled with wheels etc. and tried on running ring - a close almost tight fit as designed.  May need a bit of running in to reduce the friction though or possibly a light filing of the running ring.  One thing this proves is that I can now print as near a perfect circle as can be felt from turning the round ring in fixed wheels - there is no difference all the way round   The main thing about 3D printers is accurate setting up.

[tekkydave]

That's a work of art 

[Gina]

Thank you

[Gina]

Currently printing the rotator pinion then I'll print the bottom bit of the thick running wheel ring.

[Gina]

Here's a model of the camera end main bracket.  Printing now - hour and a half.

[Gina]

Finished printing, just waiting for it to cool and release from bed.

Shouldn't be too long now before I can set up the rig on the mount.  An unexpected clear sky tonight and I'm not ready yet   But not only cloud forecast but Clear Outside shows rain.  No point in "busting a gut" to try a hurried setup - things only go wrong - not worth the hassle. 

[Gina]

The camera end bracket doesn't come in the right position so some alteration required - no problem - it's what modelling in SketchUp and 3D printing is all about - you can try out ideas quickly.  It would need to be 15mm further out to line up with the holes but apart from the overhang on the axle, the motor wouldn't be in the right place.

[Gina]

New camera end bracket.

[Gina]

Printed fine

[Gina]

The only problem is that the objective end is too tight - the stepper motor would strip its gears.  Two possibilities :- loosen the wheels or change the motor drive (or both).  I don't want to free up the wheels too much or I might risk movement during exposures though this might not happen during the short exposures I shall be using.  Evenly filing the running ring is not easy by hand.  Maybe I should have included some form of adjustment but I didn't.

[Gina]

Been filing the running ring and now removed the slight roughness from the printing.  This was printed using 1000 faces (circles are not circles but polygons with lots of sides).  It's definitely running a bit more easily - I think possibly another tenth of a millimetre taken off will be enough.  Yes, it is that accurate.

I've thought of a way to have adjustment of wheel pressure - make the ring slightly tapered and adjust by moving the rig in or out.  Trouble is the present ring is solvent welded to the main part of the cage so can't replace it though I could perhaps glue another ring on the front of the current one.  Or just do a bit more filing