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Any drawbacks to 3d printed motorized filter wheel?


vlaiv
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I'm thinking of printing the whole thing. Well - except for motor and controller obviously

Not conversion of manual to motorized, but rather whole assembly - which is not much when you think about it - it is casing, wheel, maybe one bearing to make it move smoothly and stepper motor with controller. Maybe some sensor to find home position and that is it.

Are there any obvious drawbacks? Temperature change issues with plastic? Threads being able to carry the thing (will 3d printed T2 be strong enough to hold camera + filter wheel itself)?

Gear precision / repeatability issues?

IR leak thru plastic?

Light leak thru 3d printed structure (how well will it seal interior from light)?

Any thoughts?

 

 

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1 minute ago, vlaiv said:

I'm thinking of printing the whole thing. Well - except for motor and controller obviously

Not conversion of manual to motorized, but rather whole assembly - which is not much when you think about it - it is casing, wheel, maybe one bearing to make it move smoothly and stepper motor with controller. Maybe some sensor to find home position and that is it.

Are there any obvious drawbacks? Temperature change issues with plastic? Threads being able to carry the thing (will 3d printed T2 be strong enough to hold camera + filter wheel itself)?

Gear precision / repeatability issues?

IR leak thru plastic?

Light leak thru 3d printed structure (how well will it seal interior from light)?

Any thoughts?

 

 

My main concern would be flex in the wheel causing tilt due to lack of rigidity. How easy is it to produce your own ascom drivers, never investigated it.

Adam

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The first thing I would say is you probably won't get the accuracy in the print.

I 3D print all sorts of things at work and have tried C mount threads, 1..25" threads to name a couple, and they're ok but not great.

If I print multiple copies of the same part, they will all be slightly different. Melting plastic is not accurate.

Have you thought of the material? I have printed some small brackets in ABS, PETG and tough PLA and they're nowhere near as strong as aluminium obviously.

PLA and tough PLA is essentially cornstarch and will deform and degrade in the sunlight.

ABS is harder to print and build plate adhesion isn't easy, it curls up at the edges. It's also not UV stable so will become brittle over time.

PETG is better than ABS and should be better in UV.

Having said all that, have a go, what have you got to lose?!

Edited by Jonk
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13 minutes ago, vlaiv said:

Any thoughts?

 

 

There are some examples on thingiverse.com that maybe worth checking out. There are also parts to allow you to convert manual ones to stepper control though I noted you have ruled that option out.

I have printed a number of T2 threads on adaptors but have only mounted non-cooled ASI cameras onto them, not tried anything heavier in anger yet. I think the threads would hold a lot more but would want to test first.

Edited by 7170
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I think the threads might be an issue with the weakest direction being parallel to the layers which will be parallel to the threads almost.  I've popped parts by overtightening...  Maybe a cheap T2 extension to provide the thread?  You could use a t2-m48 adapter to provide a flange and print it into the part for strength?

I think it'll work fine to be honest.  If you have concerns then try and design the print with components that can be modified easily to allow modification where required.

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10 minutes ago, 7170 said:

I have printed a number of T2 threads on adaptors but have only mounted non-cooled ASI cameras onto them, not tried anything heavier in anger yet.

If the threads are not accurate and strong then there’s a very good chance that you will introduce tilt into your imaging train.

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IMO 3D printing is ideal for making custom parts or things that can’t readily get hold of. When you start reproducing stuff that’s easily bought then there is little benefit especially when those things like a filter wheel will take hours to design and produce.  Reality is you're better off doing some overtime at work and just buying one (but I appreciate there is some satisfaction in designing something yourself even if it is just copying what’s out there) .  When I first bought my printer all I wanted to make was custom spacers and adapters.  I was able to print the threads ok after a bit of tweaking but they leaked light even at 100% infill and in black so I lIned them with sticky back tinfoil.  Then ended up being too weak as the threads are printed in same direction as the layers.  They will absorb moisture too over time and do change shape with temp esp black material.

It’s definitely doable but when you can buy a very nice QHY EFW at £249 I do question the benefits  

 

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Definitely possible, and I've seen it done. Although I'd question hanging an expensive camera from a 3D part, even if it was printed with 100% infill. And then there's the flex to consider which could introduce tilt. Personally, I'd wouldn't make one.

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Give it a go, it will be a great learning experience for you....

You can build-in tilt correction, strengthening etc. as long as you keep an eye on the back focus... 

As for printing fine threads, yes it is possible, as long as your slicer/printer is capable of it e.g. printing at 0.05 mm layer height, but for 'production' use I'd be tempted to use brass inserts, to hold parts together, and for the inter equipment connections.

I'd base the control on an Arduino system, for which there are plenty of examples available, with motor control, positional detectors etc, and there are even Ascom divers available.

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I think your main problem will be internal reflections. I've used all sorts of PLA and tend to use matte filament nowadays as they look better, but they're still shiny to a degree. Add in the multi layer structure of prints and you've got lots of surfaces to reflect light from. Also check if your degree of infil prevents any light transmittance in the first place.

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16 hours ago, Adam J said:

My main concern would be flex in the wheel causing tilt due to lack of rigidity. How easy is it to produce your own ascom drivers, never investigated it.

Adam

Software side of things should not be a problem - it is fairly simple protocol - move to position xy and that is it.

16 hours ago, Jonk said:

The first thing I would say is you probably won't get the accuracy in the print.

Not sure what level of accuracy is going to be required here?

I've printed several types of threads down to 0.6mm pitch and they worked fine.

As far as I can tell 28 x 0.6 is going to be finest that will be printed and I've already done that. There are some clip in 1.25" filter thingies that I've printed for an acquaintance.

I'm thinking PLA as choice of material, or rather PLA+ (not sure how we should call it) - I'm currently using Creality HP ultra PLA that is produced by BASF. From what I've gathered BASF produces some very fine PLA (I've seen one review where mechanical properties were superior to other choices of PLA).

PLA has the most rigidity / least flex.

Given that it will be night time use - I don't see how exposure to sun or UV might be a problem. I'll pack the scope after the session.

Moisture absorption might be a problem and I'll have to look into that.

16 hours ago, 7170 said:

I think the threads would hold a lot more but would want to test first.

I have similar feeling. It is down to surface area, and that can be somewhat controlled.

We can do quick back of the napkin calculation.

PLA has ultimate tensile strength of about 20MPa in Z direction (up to 60-70 in non layer direction). If we select thickness of our T2 thread to be 2mm then that is (21^2 - 19^2) * pi millimeters squared or about 250mm2.

20MPa * 250mm2 = 5000N

(did I get this right?)

It seems that we would need ~500Kg of load to break it.

Even if I have poor layer adhesion and ultimate tensile strength is much less (like x10 less) - I'd be happy with that.

 

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16 hours ago, Ratlet said:

I've popped parts by overtightening...

Yep, that happened to me several times, although, to be honest, they were not designed properly (not enough walls, poor infill - small cross section).

I guess forces involved when tensioning stuff can be quite high.

 

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So far I've gathered that tilt is probably the biggest concern?

That and any internal reflections. Yes, PLA tends to be very shiny - even black. I wonder if painting it with mat paint would improve things?

Light leak is easily tested - I just need to print cover for the camera and take some darks with it on to see if they match regular darks.

 

How to go about tilt? Critical focus zone is something like 60 microns for one of my scopes I intend to use this on. That is fairly small.

I've seen "universal tilt jig" being discussed here on SGL - must look it up, maybe it will give me some ideas of what is involved and how to test for it.

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22 minutes ago, vlaiv said:

So far I've gathered that tilt is probably the biggest concern?

Tilt maybe due to flex of the parts overall, but I would suggest not from a good thread join as most astro threaded joins tend to have a nice flat surface against which the adaptor or other object compresses so its not just the threads keeping things at right angle. Even a basic T2 extension tube has two flat surfaces at the end of the threads up against each other keeping things at right angles. That has certainly been the case for the camera lens adaptors I have made too.

Felt or matt black paint should work to cut out reflections, or black stick on flocking velour.

The biggest problem is you will start work on it and during the process come up with numerous other things to make with the printer that you hadn't though of before, and your to-do list will spiral out of control (or maybe that's just specific to me!). 😀

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1 minute ago, 7170 said:

The biggest problem is you will start work on it and during the process come up with numerous other things to make with the printer that you hadn't though of before, and your to-do list will spiral out of control (or maybe that's just specific to me!). 😀

That happens to me on a daily basis :D

How do you think I got the idea to 3d print filter wheel in the first place? :D

2 minutes ago, 7170 said:

Tilt maybe due to flex of the parts overall, but I would suggest not from a good thread join as most astro threaded joins tend to have a nice flat surface against which the adaptor or other object compresses so its not just the threads keeping things at right angle.

This is actually very true - but it is also cause of concern. I might be able to to do something about it though.

At the moment - I'm seeing T2 thread on camera side being printed in such way as to mating surface being printed as last layer (top of the print). That is causing a bit of concern as it is rather rough surface.

I've played around with wet sanding paper and PLA and one can get incredibly flat and smooth finish - but I worry if I introduce tilt by sanding that part down. Need to figure out how to keep sanding paper perpendicular to optical axis while smoothing that face.

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7 hours ago, tooth_dr said:

It’s definitely doable but when you can buy a very nice QHY EFW at £249 I do question the benefits  

This is actually part of the problem :D

Knowing what goes into motorized filter wheel - I simply can't see how on earth it could cost that much, even with labor and shipping and all of that.

Yes, there is matter of scale - and mass produced items cost less and maybe they don't have marked for high enough volume - but I think I can get 3d printed version for at least x10 less money if not more.

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The biggest issue as mentioned will be creating the threads. There are a few things that all need to be parallel or concentric in a filter wheel so it might not be easy to print.

Given as a good LRGB filter set will set you back at least £400, and a single quality 3 or 5nm narrowband filter will set you back 300-500 (thinking about 36mm size here), I think it's probably not a great place to look for savings sadly.

Still, maybe money isn't the point- perhaps it's the challenge and seeing if it's possible regardless. In such a case: off-the-shelf bearings and bright steel rod could make a decently sturdy center for your filter wheel's rotating part with minimum run out. Might be a good starting point?

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1 hour ago, vlaiv said:

This is actually part of the problem :D

Knowing what goes into motorized filter wheel - I simply can't see how on earth it could cost that much, even with labor and shipping and all of that.

Yes, there is matter of scale - and mass produced items cost less and maybe they don't have marked for high enough volume - but I think I can get 3d printed version for at least x10 less money if not more.

I think you might be similar to me in that the money saving is part of the alure of building it yourself.

There was someone on here who converted a manual filter wheel to an automatic one with a stepper motor.  Perhaps that is an alternative?

I think if you go for a composite (by incorporating a T2 extension to thread onto) by using a push pull system.  You can leave slots where nuts can be pushed into the 3D print body to allow for fine tuning.  Prusa uses similar features to tune the axis on its 3d printers.

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Tilt and flex would be my first concerns like others have pointed out. Especially if you plan to stick a heavy camera behind it. Another thing is clearances inside the wheel. Too tight and a bit of flex in the casing or not so accurate bearings etc might cause the carousel to catch. Too much clearances might cause the carousel to wobble and cause all sorts of issues...The challenge is to keep the whole thing as thin as possible while being rigid enough.

In the past I started designing and making a filterwheel using aluminium parts machined with my CNC router. In the end I abandoned the project due to too many mechanical issues. I didn't want to have something stuck on my scope that would cause lost imaging sessions. In the end I went via the manual to motorized route which is still working perfectly.

Edited by kbrown
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4 hours ago, Ratlet said:

I think you might be similar to me in that the money saving is part of the alure of building it yourself.

Well that seems to be somewhat difficult to quantify in my case as there are several things at play.

As far as my self personally - it seems to be the case of "being smart enough to not have to pay that much" kind of thing. It's not so much about saving money - as have been pointed out, in grand scheme of AP things - it is not grand saving after all.

Then there is component of making things affordable to people that can't afford it. I really enjoy occasional video where people craft telescopes out of PVC pipes. Is it crude? Sure, but on some level - it gets the job done and will spark interest to someone that might not be fortunate enough to afford even cheap beginner scope.

I like to think that way - but then harsh reality hits me - in order to make some of these things - one needs 3d printer, and while they have been really affordable lately (at least entry level models) - one who can't afford beginner scope - will not be able to afford 3d printer either.

However, I've seen outreach programs where people with printers team up to make toys for children, so why not do the same for astro items - once we have good working designs.

Third part is probably due to circumstances. I live in a country that has median net income of about 500euro - yep, half of working population earns less than 500e per month. I guess I've been exposed to this "saver" culture because of it.

3 hours ago, tooth_dr said:

That is only true if you don’t put a value on your time.  

But of course I put value on it - it's my "let's design and make something" enjoyment time :D

2 hours ago, kbrown said:

Tilt and flex would be my first concerns like others have pointed out. Especially if you plan to stick a heavy camera behind it. Another thing is clearances inside the wheel. Too tight and a bit of flex in the casing or not so accurate bearings etc might cause the carousel to catch. Too much clearances might cause the carousel to wobble and cause all sorts of issues...The challenge is to keep the whole thing as thin as possible while being rigid enough.

In the past I started designing and making a filterwheel using aluminium parts machined with my CNC router. In the end I abandoned the project due to too many mechanical issues. I didn't want to have something stuck on my scope that would cause lost imaging sessions. In the end I went via the manual to motorized route which is still working perfectly.

In the end, I might give that approach a go.

I'm still thinking of 3d printing one - just for fun and to see if it could actually be used. I'll probably need to seriously beef it up to make it rigid so it won't be slim, but it might work.

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I'd be tempted to make the face plates out of mild steel or aluminum and butcher some spacers for the T2 threads, then 3d print the carcass and filter wheel.. Two metal faceplates bolted together through a printed carcass should be pretty stiff, there's no way I'd hang a camera off a 3d printed thread.

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I've decided on the course of action.

Since I'll be needing same parts for both 3d printed version and manual to motorized conversion (namely stepper and driver, permanent magnet + hall effect sensor, micro controller) - I'll go ahead and make 3d printed version just to see if it could be done. At some point in the future I'll switch components over to motorized manual filter wheel.

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Just my bit 😉. Do it ..even if just for the enjoyment of designing something unique to you. I've made many, parts,adaptors etc for my microscopes (don't do astro nowadays!) and hang my Nikon DSLR on them with no probs at all. C threads, T mounts and such like all seem fine and fit how they should. Obviously long exposures not needed with micro so flex/tilt not a problem for me but for astro not so sure😗.

Steve

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