Jump to content

Banner.jpg.b6007b69ccdf5c69bf18273ddfe023df.jpg

DIY Alt-Az mount


markse68
 Share

Recommended Posts

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

diy alt-az mount.png

diy alt-az parts.jpg

Edited by markse68
  • Like 2
Link to comment
Share on other sites

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

00C6AA59-7233-4E07-A9AD-3B4DBAB0C0B8.jpeg

30D3EC3F-0DF1-41A8-9897-E8D746CF6A5A.jpeg

  • Like 3
Link to comment
Share on other sites

Posted (edited)

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

B5343334-31E6-4828-A007-1AE83875849A.jpeg

 

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

 

72317550-9DFA-4E9A-9BF3-4C06C690BA28.jpeg

FC07943E-9C36-48AD-BAC1-82FEC73170EB.jpeg

 

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.

3685CD22-619B-4757-8382-D2F095890216.jpeg

 

They press into the printed puck

 

50E87772-C5D3-42BF-AA8A-B851287B8C23.jpeg

99FBCE14-479B-4D7C-A930-D48C9367791E.jpeg

 

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

 

0F5C351F-6742-4646-ADFD-3CC672CC737F.jpeg

89B4AA10-A841-4348-87A3-2939F9215C10.jpeg

1E13DFB4-67A0-4B1E-8A55-7FE42AD3273D.jpeg

 

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!

 

25036722-B752-456E-B661-D47E09D64750.jpeg

 

Mark

Edited by markse68
  • Like 12
Link to comment
Share on other sites

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 ?

 

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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

 

Link to comment
Share on other sites

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. 

 

Link to comment
Share on other sites

  • 3 weeks later...

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

  • Like 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.