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3D Printed Gears for Dob Altitude Bearings?

3d printing Dob DIY
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#101 designbydave

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Posted 04 March 2024 - 11:58 AM

I wonder how these gears react to changes of humidity, temperature etc. ....

Humidity should be negligible.

 

ABS plastic has somewhere around four times the coefficient of thermal expansion of aluminum, so yeah, one should expect more geometric distortions due to temperature changes over time.

ABS is a poor choice of plastic for structural parts (generally) for more reasons then just CTE. Its not particularly stiff or strong and the layer adhesion of FDM 3D printing is the weakest of pretty much all available materials, even with a heated print chamber.

 

I printed all the parts for this telescope in carbon fiber reinforced polycarbonate. According to the manufacture's data, its the strongest and stiffest "consumer grade" FDM material available. It also has a very high glass transition temperature and (should) have one of the strongest layer bonds of any materials. The CTE of polycarbonate is lower then ABS, somewhere around three times that of aluminum, BUT, the carbon fibers mixed in should significantly reduce that, maybe as close to as only 1.5 times that of aluminum.

There's a lot of "maybe"s and "should"s in there because the only way to know for sure is to load test, specifically since the structural properties of FDM 3D printed parts will depend greatly on printing specifics. However I think we can get a decent, general idea. Data from this chart - https://www.engineer...ients-d_95.html

As for this particular design, all of the critical structural elements are actual, proper carbon fiber laminates, which have a very low CTE. So, overall, I would expect this design to be quite thermally stable. So far I've tested it only on my balcony at home in temperatures probably bottoming out around 45 degrees F or so. I don't think I've observed any adverse behavior due to changes in temperature.

 

Fingers crossed for clear skies this weekend so I can get it out to the desert for some proper dark skies. There temperatures out there will be a tad lower, but hopefully not too much!
 


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#102 runcyclexcski

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Posted 04 March 2024 - 12:27 PM

Thank you for letting me know! I prob need to start experimenting with these advanced materials, too. The quality I was getting with ABS was quite disappointing, so I started outsourcing 3D printing of small precise/accurate parts to Shapeways, including metal and steel. However large sizes like yours would not be sustainable cost-wise.


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#103 designbydave

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Posted 04 March 2024 - 12:40 PM

The quality I was getting with ABS was quite disappointing...
 

 

ABS can be tricky to print. It needs an enclosure, the hotter the better, but it will still want to warp depending on part geometry. Then there's the smell. For me, it's not too bad if my printer is in a dedicated workshop, but right now I just have a studio apartment and would not want the smell in my living/sleeping space.

FWIW my experience printing the particular brand of polycarbonate I like to use is almost always amazing. A very welcome side effect of the carbon or fiberglass reinforced materials is the fibers significantly reduce the tendency to warp. The fibers seemingly give the molten material some structure while soft.

CarbonX ezPC from 3DXTech. It's not cheap but works amazingly well. - https://www.3dxtech....arbonx-ezpc-cf/

 

An alternative that's about half the price, not quite as stiff and strong but should still be good for most applications is Carbon Fiber PETG - https://www.3dxtech....arbonx-petg-cf/


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#104 designbydave

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Posted 06 March 2024 - 12:28 PM

I got the electronics setup and working. The go-to pointing isn't very accurate but tracking is pretty good. This is consistent with my previous experience with an OnStep controller that I installed in my Harmonic Drive mount.

 

 

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#105 designbydave

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Posted 09 March 2024 - 08:12 PM

The weather held for a very nice evening of observing in the California high desert last night. Not too cold either. Seeing was probably just average at best but it was good enough to finally put this telescope to work. And, wow! I am super pleased, impressed and satisfied. I made a decent jab at the "Messier Marathon", finding pretty much all the Messier objects that were visible by midnight or so. I wasn't quite feeling like pulling an all-nighter to see them all. I'll just wait until summer for the rest.

 

The go-to system had issues, mostly because the azimuth gear kept snagging on the mat I set on the ground under the telescope. I didn't anticipate that but the fix is easy, just taller feet and proper camping staked to hold the mat down.

 

That actually worked out though as I was forced to learn star hopping real quick and was able to find every object I was looking for. Kinda proud of myself for that. Having Stellarium on my tablet definitely helped, especially when identifying all the galaxies around Leo (there's so many of them!) I'm finding that I really enjoy just pushing this scope around.

 

Highlights of the night include:

  • The contrast on the Orion Nebula. That dark part in front really stood out, as well as all the surrounding gas.
  • The Whirlpool Galaxy looked pretty striking. I could kinda, maybe make out the spiral structure but only just. Perhaps with better seeing and or a more clear night. This sight tends to be a bit hazy as its down in a desert valley. I'm definitely looking forward to coming back to this object in the summer when its warm enough to go up in the mountains.
  • Accidentally "discovering" the planetary nebula NGC 2438 inside the Open Cluster M46. There are lots of open clusters in the Messier catalogue and it can feel pretty repetitive to look for them all. Glad I did though as this one held a little surprise.
  • Globular clusters are always amazing, even with low on the horizon.

I'm working on a short film to summarize this build and show some details. Hope to have that finished up in a few days.

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#106 designbydave

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Posted 10 March 2024 - 07:35 PM

Got the video up

 

https://youtu.be/diJ..._X1snV7fvSV6jdT


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#107 Dale Eason

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Posted 10 March 2024 - 07:47 PM

Very nice scope and well made video.


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#108 designbydave

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Posted 27 March 2024 - 04:15 PM

Back to work making a series of improvements.

 

First up is smoothing out the joints between the sections of the altitude gears (bearings.) These gears were too large for my (most) 3D printers, so I had to break them up into four parts. The joints where the gear teeth join aren't great. This was a problem that I anticipated, and printed a few test sections to try out. I came to the conclusion that, while this joint wouldn't be great, it would probably be good enough and/or I can hand sand, file, fill to smooth them out. That didn't really turn out to be the case and the result in practice is that there are several bumps when moving the telescope in altitude. It's not a big enough problem to keep me from enjoying the telescope, but it could be better (or perfect?)

My plan to address this is to grind the gear teeth away from the problem areas, and then re-mold them in place using a silicon mold and urethane casting resin.

 

First I'll need to test this procedure with some sample parts.

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#109 designbydave

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Posted 27 March 2024 - 04:19 PM

I 3D printed a mold box to help making the mold. I like working with silicon and it's been a while, so this is fun stuff! I ordered some cheap, small quantity mold making silicon from Amazon. The finished part is a bit tacky so maybe I didn't mix it enough, or its just crappy material but it should serve its purpose.

 

Two holes cut in the top of the mold, a fill and a vent. I used a small syringe to inject the casting urethane into the mold until material starts to flow up out of the vent. This stuff sets up quick, like 15 minutes. Heat helps.

 

 

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#110 designbydave

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Posted 27 March 2024 - 04:28 PM

De-molding is always exciting and this is looking quite promising! The bottom flange didn't cure up but I'm pretty sure that's a process error. Also I don't think I need to remove that part when grinding the gear teeth down anyway.

 

The gear teeth look perfect and the mesh is almost seamless!

 

I did an additional test with some black dye (to make sure it wouldn't inhibit the urethane curing) and with sample parts printed with the carbon fiber polycarbonate that the real parts are made with. You almost can't even tell the repair is there!

 

This is very exciting as its a really fast and easy procedure and the results should make the altitude movement of the telescope almost flawless.

 

Rain in the forecast for this weekend so I guess I know what I'll be working on.

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#111 designbydave

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Posted 04 April 2024 - 12:53 PM

We had a couple of rainy days last weekend which was the perfect opportunity to work on telescopes. I successfully "repaired" all of the gear section and things are working much better now : )

 

Here's a video of the process - https://youtu.be/Ru7...VgV_cCuqGLrACrC


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#112 spins120

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Posted 15 April 2024 - 10:35 PM

I just found this discussion board, and I had wondered if anyone had done this kind of thing yet....ABSOLUTELY GORGEOUS! Incredible skills you have! 

 

Tim


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#113 designbydave

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Posted 16 April 2024 - 01:41 PM

I just found this discussion board, and I had wondered if anyone had done this kind of thing yet....ABSOLUTELY GORGEOUS! Incredible skills you have! 

 

Tim

Thanks so much Tim

 

Hopefully more projects like this to come.
 


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#114 nekidfrog

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Posted 21 May 2024 - 06:43 AM

Just curious if you ever plan to release the model files for your design? I have a 12in ES gen 2 telescope and honestly don't like the construction of it and currently converting it to goto and finding soo many problems with the box design. I'm thinking of redesigning a new box for the whole thing and found your post and am amazed at what you've already done. I currently have a bambulabs p1s and so far printing in petg-cf has proven highly successful in making strong accurate prints that just fit.



#115 designbydave

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Posted 21 May 2024 - 08:15 AM

Just curious if you ever plan to release the model files for your design?

https://www.printabl...onian-telescope


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#116 nekidfrog

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Posted 21 May 2024 - 09:05 AM

you sir rock! and may your days ahead be cloudless and perfect!


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#117 designbydave

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Posted 03 June 2024 - 11:39 AM

Got out to Grandview over the weekend. Had a couple night of excellent observing.

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#118 designbydave

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Posted 05 June 2024 - 10:23 AM

On my most recent outing, I realized the value in using filters, mainly an O-III filter for enhancing contrast in emission nebula. Screwing in filters to the back of the eyepiece isn't the greatest experience however, as I'm sure many of you know. I had thought previously about trying to incorporate a filter wheel, or sliding tray but couldn't really figure out how to make it work with my focuser. Instead, I came up with a simple solution to use magnets to hold the filters to the inside of the drawtube.

 

I made a quick, two piece 3D Printed filter holder that clamps the filter in place. Then added magnets to both the filter holder and back side of the drawtube. It should be pretty quick and easy to attach and detach filters when out at night. Not quite as easy to use as a tray or wheel, but much better then screwing filters to be back of eyepieces.

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#119 designbydave

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Posted 07 June 2024 - 12:58 PM

I made some cases for my new filters. Having fun with 3D Printed threads. Also added magnets to the bottom, kinda just-because, but also I figure this might help prevent accidental drops in the dirt out in the desert, in the dark, when handling with gloves on etc.

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