New 2in 3D printed Crayford focuser

[marcopolo]

I'm designing and building a high quality crayford focuser. The following points summarise the main goals and design intent as it's really important when I put this design out there in the public domain ANYONE can print out these parts and it will work well.

1. Low cost off the shelf hardware, bearings etc..

2. High performance having as good as performance as any £150/$200 focuser. 

3. Aesthetically looking professional and finished.

4. 30mm drawtube travel and 38mm overall profile height fully racked in from the bottom of the base-plate to the top of the drawtube flange. Ultra low profile. Lowest i've ever seen commercially is 50mm. 

5. Can lift at least 1Kg at full extension 90deg to vertical (worst case scenario)

6. Fully 3D printed excepting fixings, bearings and bearing plates.

7. Versions of the base plate to allow different mounting styles/tube shapes etc....

Progress so for is i've done the calculations, force, moments, free body diagrams. CAD completed and completed some FEA. parts printing as of 28/5/20. details below in my blog. I'll do another update during the build/assembly.

https://marcosatm.com/2020/05/27/designing-a-high-quality-3d-printed-crayford-focuser/

 

CRAY_full assembly.avi

Edited May 28, 2020 by marcopolo
add info

[Chriske]

Nice one...!!

I'd change one thing. The focusing knob should positioned a bit higher. Fingers will get stuck while focusing. Especially in Winter wearing gloves.

[markse68]

Nice project! The base plate looks awful thin n flexible for 3D print?

Edited May 28, 2020 by markse68

[marcopolo]

Chriske, yes i'll need to see how it feels with gloves on. I cant actually raise it without fundamentally changing the force/mechanics/moments on it without maybe a geared raised pinion. A disadvantage of it being ultra low profile I guess.

Markse68, the FEA all passed at 200N (that a fairly large force) and the print feels pretty rigid to me. 5mm plate is quite thick. The proof however will be in the pudding. We'll see how it performs once it's built up. Obviously it's getting bolted to a flat wooden OTA so thickness of the base plate is almost irrelevant. I say almost because theoretically the part of the plate that's on the unoccupied side could flex away from the central drawtube area. But like I said the FEA looks pucker!!!

Edited May 28, 2020 by marcopolo
more info

[marcopolo]

That's it all assembled and running perfectly. Very smooth action. Lifts 750g no problem without a brake installed (yet).  Chriske, I've moved the focuser wheel outboard and made much larger. It's a cinch with gloves on now. 

[Chriske]

Looking good Marcopolo...
You still need to test that focusing knob using gloves...😉

And now you can start thinking on drawing V2 : adding a dual speed focusing knob to the unit...😁

[marcopolo]

On 04/06/2020 at 07:44, Chriske said:

You still need to test that focusing knob using gloves...😉

 

???Did you not see my comment?

[dallibab]

Hi I really like your design, I would like to make it but change the base so it will attach to my 8" meade sct. (It has a screw on adapter)

Do you think it would be easy to change the model to work with my tube ? would you be willing to share the original files so I can play around and try to get it working ?

 

Thanks for your time.

 

John.

[AstroMuni]

Looking good @marcopolo A question...What is the reason for keeping this piece separate?