My version of Crayford focusser for 10" Newtonian

[bojan]

For quite some time I wanted to use my 10” Newtonian for prime focus deep sky AP.
The only obstacle was low-profile focuser – to reach the focus it needded to be shorter than 35mm and I could not find anything suitable on the market, so I decided to build my own.
Recently I found time to finalise the drawings, and a friend of mine helped me to make it in his work shop. I decided to use the Crayford design because it is relatively simple to build (at least for me).
The results of that effort are attached below.. the only things that are still pending are M42->EOS adapter and a holder for the stepper motor.

The conical interface is my internal standard - long time ago, when I build my Newtonian, I sort of planned for the interchangeable back end. It was inspired by 130mm Zeiss refractor and it's mechanical design at the Astronomical Observatory I was spending my evenings on as a school boy.
The existing focuser can be replaced with this photographical one in couple of seconds.

[peter_4059]

That's an impressive bit of machining. How do you load the tension on the draw tube?

[DavidU]

Beautiful work Bojan. Well done.

[rcheshire]

Nice work. I sincerely wish I had the skills. Do you do small jobs for a fee?

[bojan]

Thanks guys, for your kind comments :)
There is no need for explicit tension control, I think.
With this design, the position of ball bearings at sides is precisely determined, but it can be additionally adjusted by means of excentric shafts so she tube is only slightly elastically deformed between the 5 pressure points, and this gives me enough friction so the tube doesn't move on it's own.

Rowland, no, unfortunately I still don't because I don't have my own machine shop yet (it is going to happen once I retire.. at the moment, for jobs like this I am using friend's workshop where I work for him occasionally on Saturdays as an advisor on anything electronic, and he is helping me sometimes with those mechanical parts).

[Shiraz]

beautiful work. a conical interface! - what a brilliantly simple idea - why doesn't everyone use it?

[bojan]

Well, Zeiss does ;) (or, used to, back in '60ies, not sure about these days)

[peter_4059]

Baader sells these conical quick change fittings (sounds like they are based on the Zeiss design). Look for Baader 2456321.

http://www.telescope-service.com/baader/adaptors/adaptors.html#wechsels

[kinetic]

How did I miss this thread B!

beautiful work, thanks for sharing, you rogue :thumbsup:;)

Steve

[bojan]

Yep, this looks like it :thumbsup: EU56.00 minus 19% tax for the set (if I understood properly) is sort of reasonable.
since I didn't have the access to milling machine back in 80'ies, I did it (with help of a friend of course) on lathe, and the internal conical details were cut out from turned parts, as needed.

[bojan]

:thanx:

[bojan]

Motor is mounted on the focuser, and the whole thing is on OTA.

Electronics will be as per Kinetic Steve (Thanks Steve for PCB :thumbsup:)

[scopemankit]

Lovely work Bojan! Do you pan to have digital readout on the eyepiece tube position?

[bojan]

Hi Chris,
yes, it will be exactly like that.
Bartels scope.exe supports focuser with stepper motor, and I have my own little program for this purpose ( I posted it here on the forum last year I think).
The limitation is, focus should be moved only with help of computer.. but it is not a real problem.
I will have pretty good resolution, 0.05 um/step. Of course, internal gearbox of the motor is not that precise (motor is CZ2801, Taiwan), but it will still be precise enough (my mirror is F5.6, so there will be some margin for error).

[coldlegs]

Great work Bojan. May I ask which supplier you used for the belt and gearing and did you have to fit a new gear to the stepper?
Cheers
Stephen

[bojan]

I obtained them from http://www.smallparts.com.au/hobby/
They are distributor for https://sdp-si.com/eStore/ , but overall they are cheaper because postage cost is lower.
Smaller (12) gear was fit to the shaft (because it was stock (https://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=50984&GroupID=345)