Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Equipment Discussions >> Mounts

Pages: 1 | 2 | (show all)
Rich V.
Post Laureate
*****

Reged: 01/02/05

Loc: Lake Tahoe area, Nevada, USA
Re: Question for UniStar Mount Owners new [Re: zawijava]
      #5149590 - 03/31/12 12:05 AM

I assure you it is not free floating! I still have a full range of friction adjustment. I'd be the first to know!

The thrust bearing just takes the frictional load off of the tension knob side of the mount. In my experience, with my scope/mount combo, this is the side of the mount that caused slop and stiction for me so I removed the source in favor of using just the large clutch surface which is quite sufficient, IMO. The non-linear friction problems went away.

As built, an equal amount of pressure is being applied to the small surface of the teflon washer under the knob as there is to the large surface of the teflon disk clutch. This friction on the tension knob side is what caused less than ideal smoothness with my Unistar. That's why I modified it.

I haven't felt the need to put a thrust bearing under the azimuth nut; the fixed tension of this axis has caused no problems for me.

I advise anyone with a new Unistar to use it for a while and break in the new friction surfaces. If, over time, you do have problems with sloppy motion or stiction, the bearing may be the answer.

Rich

Edit: Tim, upon seeing your post above, you explained it well!

Edited by Rich V. (03/31/12 12:08 AM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gordon Rayner
Carpal Tunnel
*****

Reged: 03/24/07

Re: Question for UniStar Mount Owners new [Re: Rich V.]
      #5739965 - 03/18/13 01:34 AM

There has been renewed interested in this thread, via posts in the ATM forum in the recent thread "Cheap Altazimuth Mount".

I bought a used UA Unimount Light P-Gram last year. Surprise was my reaction upon seeing an ordinary carriage bolt, with no sleeve bearing(s), for the pitch axis , and carriage bolts , with no sleeve bearings, for the P-joints.

That mount design has years of use by numerous users. Nobody has written about worn-out aluminum holes, which form the outer part of its bearings. The joint bolts and pitch bolts, and I believe the optional hinge bolt( lacking in the example I bought. I added my own, sleeved), have their threads' crests rubbing directly on their aluminum mates.

For the loads for which the Unimount light P-gram is rated, threads rubbing inside aluminum cylinder have , apparently, not been a problem. Presumably, UA have used sleeve bearings in heavier duty models. But do thread's crests rub directly there? It seems likely that they do.

In the Unistar photo which you post above, the thread crests of the elevation axis bolt seem to rub directly on the shown bronze sleeve bearing's bore. If UA use fully threaded hex headed bolts, locked into threads in the extreme right disc in the picture, as as has been seen to be UA practice in their p-mounts, then the thread crests at that side are rubbing on the bore of the disc welded to the post, or on a hidden sleeve bearing in that bore.

Perhaps UA lightly abrade the thread crests, to lessen any cutting acting on the sleeve bearing(s) or bore(s)?

This arrangement may be acceptable for the very slow turns in these applications . At higher revolving speeds, such as motors, it seems that the bearing surface would rapidly wear out, especially if the thread crests are not smooth. There would be much less contact area, so higher pressure per unit area, on the hole wall or sleeve bearing wall.

Smooth sided shoulder bolts( which cost more) have appeal , until one learns that only very short lengths of thread are on the end of available , non-custom, sizes.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Rich V.
Post Laureate
*****

Reged: 01/02/05

Loc: Lake Tahoe area, Nevada, USA
Re: Question for UniStar Mount Owners new [Re: Gordon Rayner]
      #5740572 - 03/18/13 12:02 PM

Gordon, unlike your light Unimount, my Unistar uses bronze sleeve bearings on both sides of the upright. The 3/8" SS bolt appears to be unmodified and is threaded its entire length since it is screwed in from the rotating plate side on the right.

I have a 12 yr. old light Unimount as well and so far the lack of bushings on the arm pivots doesn't seem to have caused any noticeable wear.

Rich


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gordon Rayner
Carpal Tunnel
*****

Reged: 03/24/07

Re: Question for UniStar Mount Owners new [Re: Rich V.]
      #5744340 - 03/20/13 01:45 AM

You have used a 10mm x 24mm x 4mm thrust needle roller bearing . That seems to mean that the hole in the bearing is 10mm.

10mm ( approx. 0.34 inch) is less than 3/8 inch. How does a 3/8 bolt pass? Is 10mm just nominal, and/or your bolt is undersize?


Post Extras: Print Post   Remind Me!   Notify Moderator  
Rich V.
Post Laureate
*****

Reged: 01/02/05

Loc: Lake Tahoe area, Nevada, USA
Re: Question for UniStar Mount Owners new [Re: Gordon Rayner]
      #5744891 - 03/20/13 11:10 AM

Gordon, unless I'm terribly mistaken, 10mm = 0.3937". That's close enough to 0.375" for this purpose.

Rich


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gordon Rayner
Carpal Tunnel
*****

Reged: 03/24/07

Re: Question for UniStar Mount Owners new [Re: Rich V.]
      #5745146 - 03/20/13 01:29 PM

That is the danger of working from memory only, and thinking (?) too late in the evening, as well as a cold, which must have settled in my brain: mentally misplaced decimal points/digit tranposition in metric-English conversion.

I long ago commited to memory that 25.4mm =1 inch, and that 0.039" = 1mm. Apparently, the latter was less firmly rooted.
3.14159
2.71828

The bearing source which you linked, VXB, seems to be pricing a "bearing". By this , did they mean only the cage and roller assembly, but not the washers against which the rollers bear? Or, did they mean the cage-roller assembly plus the sandwiching washers is a "bearing"?

McMaster-Carr list and price the cage-roller assembly separate from the sandwiching washers.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Rich V.
Post Laureate
*****

Reged: 01/02/05

Loc: Lake Tahoe area, Nevada, USA
Re: Question for UniStar Mount Owners new [Re: Gordon Rayner]
      #5745179 - 03/20/13 01:45 PM

The VXB offering is the complete 3-piece bearing; two flat washers and the cage/rollers, just as the photo shows.

Since they're so inexpensive, I bought several. I ended up putting one on the azimuth axis for the sake of uniformity as well...

Rich


Post Extras: Print Post   Remind Me!   Notify Moderator  
Gordon Rayner
Carpal Tunnel
*****

Reged: 03/24/07

Re: Question for UniStar Mount Owners new [Re: Rich V.]
      #5748644 - 03/21/13 10:15 PM

An order was placed for some of those bearing assemblies , and for a larger application.

What views might you have about 3/8-16, vs. 3/8-24 , as the screw for the altitude axis and/or the elevation axis?

I plan to initially try a wave washer , to preload over a range of bearing tensions in the elevation axis, in addition to the needle roller thrust bearing whose advantage you have revealed to us.


Gravity will preload the azimuth axis. There is some preload of the elevation axis also, from the couple due to the support on only one side of the load.

3/8-24 would give a finer touch to the adjustment, especially if a wave washer or other preload is not used.

But if the use of a Nylock nut is foreseen, those may be harder to find in the fine thread, though I think that I have some from Fastenal.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Rich V.
Post Laureate
*****

Reged: 01/02/05

Loc: Lake Tahoe area, Nevada, USA
Re: Question for UniStar Mount Owners new [Re: Gordon Rayner]
      #5748948 - 03/22/13 01:37 AM

Hi, Gordon, if you have access to 3/8"-24 hardware, I'd say go for it. Tension movements need to be quite small with 16 TPI; 24 TPI would give you finer control. The nylocks shouldn't wear out with the thrust bearing anyhow.

The idea of using a wave or maybe Belleville washer stacked with the bearing to preload might have some merit in this application. You may have to experiment with stacks, depending on which type of spring washers you use. Maybe they'll just make things too spongy!

Good luck,

Rich


Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1 | 2 | (show all)


Extra information
20 registered and 30 anonymous users are browsing this forum.

Moderator:  Dave M, richard7, bilgebay 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 1712

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics