DIY Alt-Az mount

[markse68]

Can't fit my Fullerscope in my new Ulez friendly car so I've been on the look out for something more compact and just purchased a very compact 8" scope that I'm picking up on Sunday, but I needed something sturdy to mount it on so I'm building an alt-az to fit on my old military tripod.

It's going to use a modified very solid cast alloy angle bracket and I'm going to use some cross roller bearings I got from my work (we use a lot of them and get them for a pretty good price from China) These are the sort of bearings used in Harmonic gearboxes. They have huge load capacity and are preloaded so there's no race play at all and no need for a second supporting bearing like normal ball bearings so that will make the construction really simple, which is good. There'll be a simple lever acting brake on each axis which I'm getting 3D printed in Nylon.

If all goes well this will be my new visual setup for taking out and about. I've been pretty exclusively playing with AP for about a year now and I'm missing using my eye to observe!

Mark

Edited April 1, 2022 by markse68

[markse68]

I made some progress on this today and it’s starting to take shape. I cut the alloy bracket to form and machined the counterbalance weight bar, although i did screw that up a bit but it’ll work just fine. Really hoping the 3D printed parts arrive this week so I can finish it in time for Friday.

Mark

[markse68]

The 3D printed parts I needed to complete the mount arrived this morning so this evening after work I put it all together.

 

The brake levers use a nylon 3D printed pad for variable friction and a rubber-cork pad for final locking- or that was the plan

 

 

They work quite well though doesn't really lock super locked- I may end up having to make the levers in aluminium for more rigidity but they do work and were a lot easier than machining them.

I had printed pucks to space the bearings off the tripod and to mount the Vixen dovetail clamp. Stainless steel Rivnuts make nice tough thread inserts with their wide top hat flanges impossible to pull out.

 

They press into the printed puck

 

 

Just a matter of screwing it all together and it's ready to use

 

 

Moon made an appearance so I'm getting first light on the new scope too which is nice- it needs to cool down though and I hadn't anticipated needing so much backfocus from the focuser so I had to vandalise my Big Barlow again to make an extension!

 

 

Mark

Edited April 5, 2022 by markse68

[skybadger]

Lovely build. Have you a summary of the cost of the parts and the overall weight ?

Have you considered lightweighting the bracket  or making it in aluminium ? Maybe these aren't important for you,  just thinking forward to my next project....

Do you have any info on what the axial  loading limit is  on the bearings , ie what the telescope weight can be. 

Also, is that simple pin locking the removable Dec arm ? Very nice. Is it very solid ?

 

[dark star]

Hi, where did you get the angle bracket ?

[markse68]

Hi Sky Badger, the bracket is an aluminium cast alloy- it’s light for it’s strength. (dark star it’s from a company called Item who make aluminium extruded profiles and this is used to join their larger ones)

Weightwise I weighed the bracket and 2x bearings at about 2.25kg. The whole assembly with tripod is about 8kg.

I don’t have specs for axial loading but the spec on the bearings for radial load is about 2 metric tonnes static. Which is quite a lot. I think it’ll take anything you could throw at it, the limitation probably being it’s held together with 8 M4 screws per race but with high tensile screws they should be plenty strong enough. Plenty for this scope which is about 7kg anyway  

Yes the weight bar has notches machined in to lock it in place with the pin. as the weight is always forcing it downward it’s plenty stable despite clearance in the slot to fit the bracket.

Mark

[dark star]

Hi, what is the diameter of the cross roller bearings and of the hole in the centre? I assume you attached it to the angle bracket using one of the circular ring of holes and to the nylon circle with the other circular ring? Where did you get the things 3D printed?

I am making a 20 inch dobsonian and the cross roller bearings look like they might be good for the altitude bearings, the design I am planning does not use the usual wooden circular altitude bearings. But I would need 2 and they are rather expensive!

I have a mni milling machine and could cut nylon circles, but the cost of the material, for example 12 mm thick nylon sheet, would not be cheap. Hopefully 3D printing is cheaper.

David

 

[skybadger]

Thanks for that Mark. I threw together a similar  thing using car  wheel bearings a while ago to hold a larger mount while I worked on it. The plan was/is to provide direct belt drive to the outer bearing surface using the belt around the we circumference which would provide the locking feature too. 

I like your approach better for a permanent capability. 

 

[Captain Scarlet]

Mark d’you reckon it’s viable commercially? Looks as if it might be to me. I for one would definitely be a buyer.

M

[JeremyS]

Impressive looking mount 👍🏻

[markse68]

Thanks Jeremy and Magnus. I’m pleased with how it turned out and it’s working well with the new scope.

Im not really in a position to make them commercially Magnus but thanks for saying that. It’s designed for that tripod which isn’t available in quantity. To make it work with a more traditional tripod would need a tall riser or extending it out further I think but it might work 🤔

Mark

[skybadger]

I'm struggling to find that large angle. Bracket, have you a link please ?

 

[Mandy D]

Wow! This looks to be an incredible homemade AZ mount. I was looking for ideas on line to build my own just last week, but never came across this. Everything else I saw was rubbish by comparison. In the end I ordered the Skytee 2 from RVO. If I ever want to build one, I think yours an excellent starting point. I wonder if a worm and wheel could be found to give it slow motion control on both axes, which could also serve as a brake. It looks like you should be able to bolt the wheel to the side of the bearing.

Thank you for posting this.

[markse68]

Thanks Mandy! I did briefly consider adding slomos to it but went for keep it simple and it’s working well as a nudge mount  

Mark

[Mandy D]

On 01/05/2022 at 19:56, skybadger said:

I'm struggling to find that large angle. Bracket, have you a link please ?

 

I don't know if you found this, already, but I'll post it for anyone else who may come across this thread and wish to build their own.

https://www.aluflex.com/Filer/PDF-Dokument/MB_Building_Kit_System.pdf

Page 96 shows the angle brackets. From the weight given, you want part no. 0.0.602.36.

[skybadger]

Thanks very much. I got in touch with sales at that vendor and strangely they weren't much use so this is great. 

[skybadger]

If you compare this with the Mesu or Hercules, those mounts both use the drive system to hold the telescope where you left it. The mesu using direct friction drive, the Hercules using a belt, both against the bearing disks. I want this bracket to replace a wooden one I made which will use an inside out timing belt around the bearing as the drive and the brake. 

[i2000s]

On 06/04/2022 at 04:31, markse68 said:

The 3D printed parts I needed to complete the mount arrived this morning so this evening after work I put it all together.

 

 

 

Mark

Where did you get your tripod? It's an interesting structure!

[markse68]

On 23/10/2023 at 21:23, i2000s said:

Where did you get your tripod? It's an interesting structure!

It’s an old military “fire control” tripod gifted me by a friend years ago. I’d hoarded it for years as i really like its construction/design and finally have a good use for it  I’ve seen a couple come up on ebay- popular with hipster lamp builders…

Mark