Big friction drive mount

[Astronomist]

Hi everyone, I thought it was finally time to start a thread on this incredibly long winded project of mine, so here goes...

This is a friction driven, ~40kg payload (in theory) german equatorial, intended to be fully AP capable. I've been slowly working away constructing it for several months now, and it's finally starting to properly take shape: 

(1L bottle for scale, and that's a 10" dob in the background)

Both axis are 50mm steel tube, running in 33210 tapered roller bearings pressed into the tubular aluminium axis housings. The mount is held together by 2 flanged steel discs that I had made by a friendly local machinist (I have no lathe or mill of my own). Overall there are many bolts that need to be shortened, and a fair few parts still yet to be made, but the finish line is in sight!

Total weight so far = 26Kg

Total cost so far = £320 (A lot of the metal was scrounged for free)

To be clear, I'm not building this mount because I want a big mount for AP, but rather because I like a project, and need something to keep me amused in the long periods of cloudy weather and daylight...  If I end up with a good piece of astro gear at the end, so much the better!

I will post updates on the build progress in this thread as and when some stuff gets done, which might not be for some time.

Clear skies!

Edited Sunday at 07:13 by Astronomist

[fwm891]

Great project.

The Dec rollers at the top? what function are they intended for, just seems an odd placement?

[Vroobel]

Congratulations! 🤩

I know that it's too early for it, but I'm full of respect for people building their stuff. I believe you will be able to get decent tracking and guiding. In 2021-2022 I was building a 90kg EQ fork mount and it was quite good, but finally I ended up with a Celestron CGX which is incomparably lighter and easier in assembling. 

Did you decide about the electronic side of the project?

Keep us informed!  

 

[TiffsAndAstro]

This looks very cool. Also doesn't look home made (well most of it)

Let us see some results when it's up and running.

[Astronomist]

9 minutes ago, fwm891 said:

The Dec rollers at the top? what function are they intended for, just seems an odd placement?

They will drive the dec axis, I put them in line with the RA axis so the weight won't affect the balance. It would have been Ideal to have the entire Dec disc, rollers, and motors at the counterweight end of the shaft, but this would have caused difficulties with the (as yet non-existant) altitude adjustment mechanism.

@Vroobel Your fork mount was one of the things that inspired me to start this project; It's an impressive beast! The electronics will be Onstep, I haven't decided yet if I will build an onstep system or buy an off the shelf kit, I'm not as confident with electronics as I am with mechanics.

Edited September 30 by Astronomist

[Vroobel]

Wow... ☺️

I based my OnStep controller originally on MKS Gen-L (v.2.1) board, but it's nothing better than the Arduino. Later I moved to FYSETC S6 with the hope that slew could be faster, but it wasn't much faster because of two gearings I used both in RA and Dec axes, so I gave up. In the end, not the slew is the most important thing.   I modified my EQ5 to OnStep using the MKS Gen-L board and it's a very nice and accurate 'small' second mount. In both cases, I didn't plan using anything else than a USB cable.

 

Edited September 30 by Vroobel

[Albir phil]

Hi this is a similar mount I built quite a few years ago for a 12 inch macsutov

[TiffsAndAstro]

Love the mechanical made for a purpose look. 

[Albir phil]

1 minute ago, TiffsAndAstro said:

Love the mechanical made for a purpose look. 

Yea it was a beast , purely manual weighed about 400lb when finished 

[Peter Drew]

Another friction drive mount.  One I built for my 8.5" refractor

[Astronomist]

Wow, those are some impressive mounts (and scopes)!

Is that a binoscope in the background of the second pic @Albir phil?

[Vroobel]

I see here a lot of talented constructors! 😁👏

 

[Albir phil]

34 minutes ago, Astronomist said:

Wow, those are some impressive mounts (and scopes)!

Is that a binoscope in the background of the second pic @Albir phil?

Yea 6inch

[Astronomist]

45 minutes ago, Peter Drew said:

Another friction drive mount.  One I built for my 8.5" refractor

Did you experience any issues with dirt or debris getting on the friction disc? This is something I am slightly concerned about as both the Mesu and JTW mounts are said to be sealed from dust ingress.

[Vroobel]

You could use a small brushes on both sides of driving axes. 🤔

[Peter Drew]

4 hours ago, Astronomist said:

Did you experience any issues with dirt or debris getting on the friction disc? This is something I am slightly concerned about as both the Mesu and JTW mounts are said to be sealed from dust ingress.

No issues as yet, the contact surfaces are stainless steel so no need of any dust attraction preservative.    🙂

[Astronomist]

I got some work done on the mount this afternoon, made and fitted some brass pieces to stiffen the RA-DEC axis junction point. This was one of very few parts that fitted exactly right first time. 😎

The perfectionist in me says some further trimming of the length is needed...

 

 

[Astronomist]

I spent most of saturday working on the mount in the lovely sunshine, I got several parts made for the altitude forks, and trimmed the brass pieces on the axis junction to line up perfectly with the grooves in the disc. OCD is satisfied.

The mount now stands up by itself on the Alt forks without any clamps or bits of scrap aluminium keeping it in place. Below is a picture of some crude and ugly parts I made yesterday that stop the clamping nuts rotating inside the RA housing. The weather has been so bad today that I needed the camera flash!

It doesn't show that well in the picture but the weight of the mount was bending the 3/4" plywood work table quite noticeably!

 

Edit: just realised how bad the bokeh is in the first pic. serves me right for being lazy and using the camera on full auto.

Edited October 6 by Astronomist

[Vroobel]

I have a question, are the most bottom parts made with rectangular profiles? If yes, did you place any spacers (tubes) between their walls before you placed the bolts there? If not, screwing the bolts will squeeze the profiles which will result in a smaller friction and stability. Sorry, if it's obvious and you already did it. 

[Astronomist]

They are indeed rectangular profiles, and there are spacers. There is a large rectangular steel spacer inside each fork that both bolts pass through, which has the added benefit of spreading the load from the bolts over a wider area of the housing.

[Astronomist]

I've just finished cutting (with a jigsaw) the baseplates for the mount out of 5mm 1050 aluminium plate. I really wish I'd spent a bit more and used 6061 instead, the 1050 is like blutack. The top 2 plates will be epoxied together and have the mount's atitude forks bolted to them , while the bottom one will be stationary and fixed to the pier/tripod. 

In other news I have obtained a really beefy steel beam with 10mm plates on either end. This should provide a solid base for the mount, at least until I can sort out something lighter and more elegant. 

Next thing on the to do list is the altitude adjustment system, which will be based around a M16 x 1.5 stainless threaded rod.