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Chasing 3d printed astro threads?


vlaiv

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What to do it with?

Are there any readily available tools that can help?

I had a host of requests to print small Canon clip holders for 1.25" filters.

1.25" is M28.5 x 0.6mm. That is very very fine pitch to be printed on the 3d printer. I printed those with 0.08 layer height - which gives something like x7.5 layer per pitch. That is enough to form decent thread - but issue is, at those layer heights extrusion becomes unreliable.

That is too small amount of filament to be extruded. Both e steps per mm and also filament tolerance play a part and surely - threads don't look very nice - there are these odd bumps here and there that need to be cleared out.

Now, I haven't designed these threads to suit my printed - I just downloaded STL from the net.

It is a nightmare to clean up and screw in filter in those. I have blisters on my fingers from trying to clean up threads with filter cell alone, and I'm only half way thru the batch (9 filters in total - and I managed to get 5 of them functional - with 1 not being able to thread all the way in).

Is there any tool that can help with this? Any sort of thread file that I could use or thread chaser or anything for non standard pitch (As far as I can tell M3.5 has 0.6mm pitch from standard metric threads).

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Normal practice with metal threads after tapping the thread would be to use a "thread chaser".  Thread chasing tools look similar to a tap used to cut the thread but have cutting angles and clean outs to remove debris.  If you can find one of the appropriate dimensions it would also work with plastic threads, just be very gentle. May also be a bit of an expensive option. 

Thread Chaser Link

Jim 

Edited by saac
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Just a thought, may work, you could try a thread cutting oil with your existing technique.  I t may work, equally the cutting fluid my not be compatible with your plastics so maybe a test would be sensible.  The cutting fluid, if it works, should ease the pressure when cleaning out the thread.  Maybe wroth a try - could experiment with your own DIY cutting fluid !

Jim 

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1 hour ago, saac said:

Normal practice with metal threads after tapping the thread would be to use a "thread chaser".  Thread chasing tools look similar to a tap used to cut the thread but have cutting angles and clean outs to remove debris.  If you can find one of the appropriate dimensions it would also work with plastic threads, just be very gentle. May also be a bit of an expensive option. 

Thread Chaser Link

Jim 

Problem is - thread chasers tend to come in standard sizes.

There is no thread chaser nor tap for M28.5 x 0.6

This Old Tony has neat trick to cut internal threads with tap of smaller diameter: https://www.youtube.com/watch?v=f-YWsgAHR6A

I was hoping there was such a trick that I could use on astronomy threads with something like thread file or similar.

From what I've seen - thread chasers tend to be standard threads and bolts with cutting faces cut into them. Maybe if I take empty 1.25" cell and cut couple of groves for cutting? Maybe that will help?

Although, on better inspection - it seems that thread form on this adapter is not properly modeled - I'm doing my own model at the moment and will add proper thread profile to it. Maybe that will do the trick.

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Vlaiv I don't know if you ever checked out the Fusion 360 astro thread script by @Paul Gerlach. I've used Paul's script when I built one of his low spec spectrometers and I found his threads to print really well.  I think my previous suggestion of custom thread tap would be a non starter - prohibitively expensive no doubt. 

Jim 

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Sounds like the ones I did a while back and sold on here. I got them printed  sls in nylon.

For wee parts like that it works out quite cheap as long as you order 20 or 30.

You get th definition/resolution u need for the threads, plus the more tough nylon.

If u insist in doing yourself in pla, is suggest coating the thread in ethyl acetate for a few minutes before then cutting the thread via your filter - it will soften the pla and let it move into the shape of the thread easier.

For SLS though, I used 3dpeople.uk

 

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21 minutes ago, saac said:

Vlaiv I don't know if you ever checked out the Fusion 360 astro thread script by @Paul Gerlach. I've used Paul's script when I built one of his low spec spectrometers and I found his threads to print really well.  I think my previous suggestion of custom thread tap would be a non starter - prohibitively expensive no doubt. 

Jim 

No, but proper metric threads are rather easy to model.

I do it in FreeCad in just few steps. Create spreadsheet to do necessary calculations (mostly just finding out respective major and minor radius depending on pitch and major diameter) and then simply create profile that I either cut into or add (subtractive or additive helix trace) - depending on how I want to model.

My printer feels good with 0.1mm tolerance per radius (which is 0.2 per diameter) over nominal thread size. This works for both mating printed threads and mating printed thread with manufactured one. I've done threads down to 0.7mm pitch so far (m4 threaded holes) - this will be first time that I attempted to print my own 0.6mm pitch thread.

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Such threads are usually turned with insert tools on a CNC lathe as they're so fine, you'd struggle to achieve a consistent machined thread across parts with something like a tap, it's a non standard thread form anyway. Your main issue if you can print at such a fine size is having the thickness of material in the thread max pitch, any mating contact will likely bind and damage the thread.

If you can achieve the thread via print, I've found printing with the object standing upright forms the thread better rather than it being flat forming the thread in a circular pattern.

Depending on what you're making I would have thought you could get a pre machined aluminium adaptor, and undersize design a fitment hole and sink the aluminium part into the print as a post operation via heating, but that adaptor is what I'm assuming you're trying to print in the first place.

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1 minute ago, Elp said:

Depending on what you're making I would have thought you could get a pre machined aluminium adaptor, and undersize design a fitment hole and sink the aluminium part into the print as a post operation via heating, but that adaptor is what I'm assuming you're trying to print in the first place.

I'm not doing anything fancy.

Couple people from my local forum contacted me for simple EOS filter clip for 1.25" filters.

Apparently, these are being printed and sold:

https://www.teleskop-express.de/shop/product_info.php/info/p14030_Wega-Clip-Filter-for-1-25--Filters-on-Canon-EOS-APS-C-Cameras.html

(note in description: "Dimensionally stable up to 110 °C due to the use of special PLA for 3D printing" - LOL)

and to get them here one would need to pay something like 70 euro.

I'm printing them for like x1000 less in plastic cost :D (granted - I do end up charging 1 euro per piece for all expenses - plastic, electricity and wear and tear on 3d printer).

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You could likely get away with a coarse(r) pitch. Those prints look rough. Try to print only 1/1.5/2x turns of thread, you'll give yourself more room to print, and you can strengthen the thread slightly by putting rads at the base of the thread. You can address the upstanding filter by raising the resting face of the print for it to stop against.

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If you are doing a lot and doing it frequently then it may make sense to seek out a local machine shop. The could effectively turn you a bespoke thread. It wouldn't need to be a cutting thread just a regular thread given that you would be using it to chase through plastic. They could even put a T bar on it so you could easily turn it by hand without recourse to using a spanner.  Time to make friends with somebody who has a metal lathe :)  I'm planning on acquiring one for my retirement but that is a couple of years away yet :) 

Jim 

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I've successfully printed a lot of 0.75mm pitch threads in various sizes with my Prusa Mk3 with a 0.25mm nozzle and 0.1mm layer height in PETG. Haven't tried 0.6mm pitch though.

What I find often is that I have to print external threads a little smaller than the nominal size and internal ones a bit bigger to have a smooth running tolerance between them.

Not sure if you've seen this already in another thread but I made a simple macro for FreeCAD for making metric threads of any diameter and pitch. It has a "tolerance" parameter you can play with to get a good fit for your prints:

thredster.zip

Note if you choose internal thread mode in the macro, it will give you a cutter to be used in a boolean operation to make your actual thread.

Edited by kbrown
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It looks like it was down to tolerances and thread form.

Once I've made my own model - where I could tweak tolerance and which had proper thread form - I can now thread 1.25" filters without too much problems.

I still have some resistance on first few goes - but once threads are additionally formed - it works fine after.

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