Linear motion components for DIY focuser?

[Chriske]

If I may...

A bit more travel, say 30mm (maybe even more) would be better imo.
The eyepiece barrel OD is 36mm, the upper ring hole is 36.2, that might be a little bit tight.
Glueing a few sheet of very thin copper should eliminate that roughness while focusing. Thickness about 0.05mm. Something like this.

[vlaiv]

4 hours ago, Chriske said:

A bit more travel, say 30mm (maybe even more) would be better imo.

That can be easily adjusted - focuser travel is draw tube thread length - focusing knob thread length (provided that we opt for 100% engagement all the time).

4 hours ago, Chriske said:

The eyepiece barrel OD is 36mm, the upper ring hole is 36.2, that might be a little bit tight.

It looks like I have good dimensional stability / accuracy with my 3d printer then ?

4 hours ago, Chriske said:

Glueing a few sheet of very thin copper should eliminate that roughness while focusing. Thickness about 0.05mm. Something like this.

That is interesting idea. Here is recording of how it works now:

That strange background music is coming from a TV in the other room - but all you can hear is focuser and my breathing - it is rather quiet in operation, but you can get the sense of it not being smooth from the recording.

 

[Chriske]

Vlaiv, have you considered adding a dual speed knob yet..?

[vlaiv]

12 minutes ago, Chriske said:

Vlaiv, have you considered adding a dual speed knob yet..?

To which one? Not sure how can I add it to helical one.

But I did consider doing anti backlash thing on it with split rings and springs.

For regular focuser - one for achromat, I won't bother with dual speed. I'm aiming somewhere in between. Say that with regular focuser, travel is around 20-30mm per turn, and with 1:10 reduction - that is 2-3mm per turn.

I'm aiming for 10mm per turn - so it will be somewhere in between of "normal" and reduced. It won't be as slow as reduced when needing to rack considerable distance, yet it will be finer than regular one in focusing.

[Chriske]

I'll have try with your non rotating helical focuser if I'm allowed to...?

1 hour ago, vlaiv said:

To which one? Not sure how can I add it to helical one.

 

[vlaiv]

2 minutes ago, Chriske said:

I'll have try with your non rotating helical focuser if I'm allowed to...?

 

Not sure what you are asking?

If you want to reuse and modify the design - sure, I here by declare it public domain and you are free to do whatever you want with it. There is FCStd / FreeCad project attached in one of previous posts - so you can load it in FreeCad and modify / export it to suit your needs.

How do you plan to do it? I'm rather curious.

One way possibly would be to add planetary gear arrangement around second focus ring? But that would make focus rings very thick compared to the rest of assembly?

 

[Chriske]

It' only now that I see these printed rings are sold for 233€ ....😳. That is INSANE...!
Did a simulation and that very same ring cost me about 2.5€ and on top of it I made it far more thicker then teleskop-express's  ring.

https://www.teleskop-express.de/shop/product_info.php/info/p14170_TS-Optics-plastic-tube-rings---made-to-measure-for-tubes-up-to-180-mm-diameter.html

[Chriske]

15 minutes ago, vlaiv said:

I here by declare it public domain and you are free to do whatever you want with it.

Thanks a lot..!

I only need a proper name for your design. Credit where credit is due..!

What about 'Velical' focuser..?...😁😉

Edited December 12, 2022 by Chriske

[vlaiv]

2 minutes ago, Chriske said:

.😳. That is INSANE...!

Yes, many 3d printed parts cost insane money from DIY perspective.

If one wants rings - it makes more sense to invest in ender 3 and some filament and print them for themselves for same sort of money

But I guess if someone runs a 3d printing business, then there is all sorts of overhead / costs - "labor" carrying most of the cost. Second being merchants profits

I printed 4 of these for an acquaintance from a local forum for free (it costed me something like less than euro in material and power)

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

"Original" with shipping would cost something like 65 euro per piece

 

[vlaiv]

4 minutes ago, Chriske said:

Thanks a lot..!

I only need a proper name for your design. Credit where credit is due..!

What 'Velical' focuser..?...😁😉

How about "Screwy Vlad" focuser (it is thread based after all) ?

Well, name it as you see appropriate, I won't mind one way or another.

[Chriske]

I take that as a yes...😉

And if my dual speed system is approved by you we call it Velical-C...

[Chriske]

I also have a idea to eliminate backlash on this focuser.

[vlaiv]

4 minutes ago, Chriske said:

I also have a idea to eliminate backlash on this focuser.

It will be interesting to see what you came up with.

When I was thinking about it - here is what I envisioned as a solution:

it is based on above principle - spring with two threaded parts.

So - two threaded parts - one "attached" to outer focusing ring, while other free - but supported with several thin pins (like 2mm steel pins) - each of which has spring around it.

[Chriske]

I use(d) these  brass backlash nuts all the time in my 3D printers beds. Recently I removed the smaller part and the spring of these units, because not working properly on my latest printer 300x300x500. I screwed a 1kg steel disk under the heatbed instead. Backlash problem solved.

 

[Alien 13]

9 hours ago, vlaiv said:

It will be interesting to see what you came up with.

When I was thinking about it - here is what I envisioned as a solution:

it is based on above principle - spring with two threaded parts.

So - two threaded parts - one "attached" to outer focusing ring, while other free - but supported with several thin pins (like 2mm steel pins) - each of which has spring around it.

My Ender 3 has these on both of my dual z axis rods, absolutely brilliant especially as I like to "hop" a lot between layers sometimes.

Alan

Edited December 12, 2022 by Alien 13

[vlaiv]

Design stage of prototype / proof of concept is finished.

I already printed some parts, but there is more to be printed before assembly.

So far, I've spotted some things that will need to be changed for actual focuser:

1. With this arrangement, focuser will work "backwards". Since there is reduction stage, there is also reversal of rotation motion, so as is - this functions in reverse to standard Crayford / rack and pinion with regards to "rack in" and "rack out" knob motion (what we are used to as "racking out" - will actually move draw tube inwards and vice verse). In final design I'll need to add idler gear to reverse rotation direction once more

2. Due to need for additional shaft for idler gears, and since it also needs to be suspended on some bearings - I'll need to switch from 608 bearings used in above design to smaller bearings.

I'll either need to source some really tiny bearings, or maybe again use bushings for these shafts as well. This would mean also switching from m5 threaded rod as shaft/shaft support to maybe 5mm or smaller smooth rod (which I'd need to source somewhere - aliexpress has many listings for such things - but that is another 40-60 days of wait ).

I tried the idea of 3d printing shaft to be used with bushing and found:

- tolerance must really be dialed in. I managed to get close after 6 attempts

- tolerance goes out of the window as soon as I change seam position / algorithm. Aligned creates smoothest surface - but leaves well - seam along length of the shaft and that can be felt when rotating as bushing also have groove - when too meant there is a "bump". Using random creates much worse looking surface finish (and probably feel of rotation - did not try that because using random seam position throws off tolerance and it also needs to be dialed in).

[vlaiv]

Here is "contraption" in action:

 

I've learned a lot by making this.

First - 3d printed gears work and work well.

Second - I can use m5 threaded rod as shaft - provided I actually 3d print "screw on" sections of the shaft. If I don't do that - things will bend and shift around, but once I create "train" of gears, spacers and press fit thingies for bearings - everything just works as it should.

I did not make focusing knobs with press fit tolerance for 608 in above setup and it feels - there is a bit of play because of it - on the other hand, second shaft is smooth and does not move a bit.

In any case - I would not mind using this as focuser mechanism at all. Even the fact that it runs "backward" - is really not that objectionable - once at eyepiece - we don't really think in terms of "rack in" and "rack out" - we just move focuser in direction where things get sharper (star images smaller).

It runs smooth and audio in above recording does not do it justice. Probably because it is so quiet that phone had trouble recording it (its not silent, especially in part where I force "draw tube" in and out, but it is quiet).

BOM:

2x180mm long 6mm linear rods

4x SKF 6mm PTFE bushings

4x 608 bearings

2x 100mm (but should be less) of m5 threaded rod

In final design, I'll probably secure focusing knobs with few m5 nuts as well, and possibly exchange one pair of 608 for 8mm PTFE bushings (or not - it will depend on available space / size of the unit).

Linear elements (in this instance rods) for focuser and smooth motion - PASS! (flying colors I might add).

[vlaiv]

.... meanwhile (also using linear motion components) ....