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3d printing for astronomy - a video

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#1 Lognic04

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Posted 24 March 2020 - 03:58 PM

Hi all,
In light of sharing astronomy and telescope making, I've been making videos on different topics lately. Here's mine I just made on 3d printing, an exciting technology for telescope makers!

https://youtu.be/stZlq4b0dhY

Cheers,
Logan
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#2 LarsMalmgren

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Posted 24 March 2020 - 05:19 PM

Excellent !

 

I have the same 3D printer, it pretty easy to get running.

I'm experimenting with fine threads like the M42 (old lenses), T2 and 2" filter thread.

That's a bit challenging but not impossible.

 

Mostly it's about getting the tolerances right (accounting for the PLA size creeping when it cools)

and having the printer print clean lines without oozing or stringing.

 

Cheers!


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#3 copper280z

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Posted 24 March 2020 - 05:34 PM

I haven't watched the video yet, but both my Dob and my imaging setup have a bunch of 3d printed parts.

 

The Dob has the mirror cell and the tube/alt box mount 3d printed. The imaging setup has a 3d printed guide scope and is about to have a 3d printed mount for a stepper focus motor.


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#4 Arjan

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Posted 24 March 2020 - 05:34 PM

Very nice indeed Logan!
As you say 3D printing will change a lot of things. I have done what you suggest, buy 3" Mak optics from SS and print almost the complete OTA. Yesterday I've tried it on the stars and it works fine.

Lars, can you detail on how you get the threads done on an Ender 3? It is the last bit I am missing for a full 3D printed scope ... 😁
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#5 Lognic04

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Posted 24 March 2020 - 05:34 PM

Excellent !

 

I have the same 3D printer, it pretty easy to get running.

I'm experimenting with fine threads like the M42 (old lenses), T2 and 2" filter thread.

That's a bit challenging but not impossible.

 

Mostly it's about getting the tolerances right (accounting for the PLA size creeping when it cools)

and having the printer print clean lines without oozing or stringing.

 

Cheers!

Thanks!

That's something that definitely interests me as well. Could be great to make threaded parts!



#6 Lognic04

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Posted 24 March 2020 - 05:36 PM

I haven't watched the video yet, but both my Dob and my imaging setup have a bunch of 3d printed parts.

 

The Dob has the mirror cell and the tube/alt box mount 3d printed. The imaging setup has a 3d printed guide scope and is about to have a 3d printed mount for a stepper focus motor.

That is similar to what i have for my imaging setup - it all mounts to one 3d printed part. Including stepper bracket!

 

Very nice indeed Logan!
As you say 3D printing will change a lot of things. I have done what you suggest, buy 3" Mak optics from SS and print almost the complete OTA. Yesterday I've tried it on the stars and it works fine.

Lars, can you detail on how you get the threads done on an Ender 3? It is the last bit I am missing for a full 3D printed scope ...

Thanks! I am definitely excited to see what the possibilities are.



#7 JoeVanGeaux

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Posted 24 March 2020 - 07:25 PM

Very nice indeed Logan!
As you say 3D printing will change a lot of things. I have done what you suggest, buy 3" Mak optics from SS and print almost the complete OTA. Yesterday I've tried it on the stars and it works fine.

Lars, can you detail on how you get the threads done on an Ender 3? It is the last bit I am missing for a full 3D printed scope ...

Interesting projects! 

I am trying to get my newly acquired Meade ETX-90 MAK up and viewing, and will be printing stuff for it soon, no doubt.  However, could you post a pic or two of that printed scope?

I have come to the conclusion that I should not be printing parts that I can re-purpose from other source materials (e.g., plastic pipe/tube, small screws, bolts, etc.)  I have been focusing on designing and printing parts that often glue, screw or otherwise hold themselves onto other parts that I didn't have to wait for a day to print.

 

All the best!

Joe



#8 Dale Eason

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Posted 24 March 2020 - 07:42 PM

I have tried and failed to make small threads like used on optical filters in camera world.  I will be interested to see if it really can be done.

 

However I do use the printer from many other things.  


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#9 Lognic04

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Posted 24 March 2020 - 10:17 PM

Definitely would be useful to see 3d printed adapters and such. I guess the main issue would be strength and which orientation the thread in printed in relative to layer lines.



#10 Dale Eason

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Posted 24 March 2020 - 11:10 PM

The main issue for me is that each thread is an overhang.  So you have to use a filament that can create overhangs without support.  My favorite is PETG and no way it can do that.  At least not for me.  Tried PLA but you need fine layer height and small nozzle I'm guessing.  My min layer is .1 but I have a .5 nozzle.


Edited by Dale Eason, 24 March 2020 - 11:11 PM.

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#11 LarsMalmgren

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Posted 25 March 2020 - 05:26 AM

I'm still investigating but have some success.

My intension was to do some kind of write-up of my findings and put it somewhere.

 

So for now i can't give a final golden recepee but i can give you some bullit points.

 

  • Your 3D printer need to be calibrated.
    That is calibrated e-steps, retraction, speed, temperature (for the specific filament), bed leveling and hole size calibration (dimensional accuracy).
    Last one i have skipped, tried to cut a corner. But slowly realising that i need to do it.
    So basically fine-tuning of your printer.
  • I slice at finest detail, for me that is 0.12 mm layers.
    Someone calculated the layer height for 1 full-step of the motor on Ender 3, and it is 0,12 mm.
    The claim is that layer heights that are not an integer number of steppes on the motor would produce incosistant layers in the printed part.
  • I use 0.4 mm nozzle, should be ok, but i might try a smaller nozzle.
    It's a trade-off since finer nozzle means much slower prints, but maybe thats the price to pay.
  • I do everything in PLA. I have some PETG but so far not used it.
    Ahh yes, part cooling is a must. Ender 3 has that out-of-the-box.
    I still use the standard but i will at some point print a better part cooler that blows from both sides of the nozzle.
  • You need to learn how to draw the threads in your favorite 3D drawing application.
    I use Fusion 360 and it has a neat thread tool. Lots of different thread types in the software out-of-the-box
    Unfortunately NOT the fine threads (1 mm and smaller pitch sizes)
    You can add custom threads but it requires knowledges to create 1) xml-files in certain format, 2) the actual sizes of thread diameters (there are several), pitch AND tolerances!
  • I'm working on a spreadsheet that can calculate these sizes for metric threads.
    There are some formulas on the net, ISO standards etc that can be looked up.
  • Printing male threads are the easiest, female i'm still working on.
    I'm fairly sure that it because the printed part schrinks a little when it cools.
    For a male thread it just adds more tolerance. But for the female it just gets too small.
    This is where i'm still experimenting and where the lack of the hole accuracy calibration is showing.
  • Oh yes, research or measure what the size of the thread you need actually is !
    This can be a bit of a nightmare. For instance 2" filters, what is the thread size?
    Well, the diameter is 48 mm (yes, it's actually metric even if we call it 2").
    But the pitch can vary. Seams that Orion (USA) uses a 0.6 mm pitch where everyone else uses 0.75 mm pitch.
    Well except for Baader it seams. They choose to use a non-public pitch size so their filters, adapters and what not can fit most all other brands.
    I guessing that Baader use a 0.7 mm pitch, but not sure.
    Another one is the difference between the old Pentax screw mount M42 and the astro T2.
    Both are 42 mm diameter. But the Pentax is 1 mm pitch and the T2 is 0.75 mm pitch.
    And so it goes on and on and on....

 

I have succesfully use an spacer/adapter of my own design between an old Takumar 135mm lens (M42) and a QHY camera (T2).

I have also designed an adapter the goes on a lenses front filter thread (M58) and takes a 2" filter (M48).

I have less success with designs downloaded from the net. Not sure why. Maybe the public designs are optimized for a specific printer...

Maybe i just need to practice more smile.gif

 

I can put up a few pictures later.


Edited by LarsMalmgren, 25 March 2020 - 05:32 AM.

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#12 Arjan

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Posted 25 March 2020 - 08:08 AM

"So for now i can't give a final golden recepee but i can give you some bullit points."

 

I guess there is no such thing as a golden rule in 3D printing wink.gif

I have been fiddling with PETG for ages before getting stable results. PLA seems to be a bit easier.

 

So what I was curious about is, how doe you deal with thread and layers being under an small angle, don't you get steps in you thread surface? Even 0.12mm seems to be a lot compared to 0.75mm thread.

I was thinking, maybe ABS would be better, because you can smooth the surface in acetone fume. Or you could actually make it too tight, and lap the thread after printing?

 

Alas, FreeCAD does not have any thread support (that I know of anyway).


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#13 LarsMalmgren

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Posted 25 March 2020 - 08:29 AM

The steps doesn't seam to be a problem.

If i run a nail into a groove and track it back and forth in the thread i can only slightly feel the steps.

 

You could use a tap or dye to clean-up the threads.

But how many have a M48x0.75 tap for instance?

 

If your software don't have a built-in thread tool then you can draw them manually.

Take a look at this video > https://youtu.be/1nhcKn7Kt8w

 

What makes PETG harder to use?

ABS requires a printer enclosure to keep the air temperature high and avoid draft.


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#14 Augustus

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Posted 25 March 2020 - 10:56 AM

PLA can melt, fade and crack in heat/sunlight overtime. Not the greatest choice for lots of scope parts.



#15 LarsMalmgren

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Posted 25 March 2020 - 11:35 AM

Well true, the theory says so but in practice people have printed lots'n'lots of PLA and used it outdoor for several years.

And how much sun does a printed adapter get during night?  But for solar it's for sure a no-go!

Maybe if you live in a tropical environment with lots of heat during the day combined with a permanent setup in observatory.

Might accelerate wear and tear.  Certainly worth having into consideration.

 

For me, i live in a relatively mild/cool Scandinavia, so that's not a problem for me.

When the part start to show signs of age, then I just print a new one.

I think one of my adapters is 16 or 17 grams. Maybe 50 cents in filament.

 

Well i bought the PETG for better durability.

Just haven't gotten to it yet :)


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#16 Arjan

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Posted 25 March 2020 - 02:06 PM

What makes PETG harder to use?

ABS requires a printer enclosure to keep the air temperature high and avoid draft.

PETG has different characteristics. It requires higher temperatures and is more fluid, so it tends to ooze a lot and produce a lot of unwanted stuff. In my case it didn't attach to the bed, until I started to use adhesion spray. Then I got clogged up hot-end, due to too large retractions. This also caused thermal issues and emergency stop during printing.

 

The optimum settings have lower tolerance than PLA.

 

The prints I get now are quite good; fairly well defined and very strong.I am still struggling a bit to get the dimensions spot on, you can change both the feed percentage (depends on actual filament diameter) and XY dimensional compensation. The first determines over/under extrusion, the latter is an addition to XY dimensions to get holes and other things the right size. IMO it should not be needed, but it can help you out.


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#17 iwannabswiss

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Posted 25 March 2020 - 02:14 PM

The main issue for me is that each thread is an overhang.  So you have to use a filament that can create overhangs without support.  My favorite is PETG and no way it can do that.  At least not for me.  Tried PLA but you need fine layer height and small nozzle I'm guessing.  My min layer is .1 but I have a .5 nozzle.

Or use a dual extruder and PVA filament, which is water soluble.  I've never tried it, but it gets good reviews from the ones I've seen.  Could open up some new doors for those interested.



#18 Dale Eason

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Posted 25 March 2020 - 04:07 PM

Most printers at present are single extruders.  So that requires modification or a new printer and a new learning curve for processing duals.  But if you got it try it out.



#19 iwannabswiss

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Posted 25 March 2020 - 05:09 PM

That's true.

 

Then the other alternative is to get the Mosaic Palette 2S, which doesn't require buying a new printer or modification of your existing single extruder.


Edited by iwannabswiss, 26 March 2020 - 04:23 PM.


#20 Lognic04

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Posted 25 March 2020 - 09:58 PM

Thanks for the interesting discussion! Now i'm thinking about reprinting my 6" mirror cell as i have some issues with it. Could be interesting!

 

I also picked up a kilo of clear PLA (looks more translucent though), some interesting things could be made for sure.


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