Question for UniStar Mount Owners
Posted 29 March 2012 - 06:35 AM
Posted 29 March 2012 - 11:11 AM
What you describe does not sound like my experience at all, and I would suggest calling Larry at UA. He is a great guy to deal with, and he will make it right in my experience.
Posted 29 March 2012 - 11:24 AM
I've got the same setup as you (EON120/Unistar Dlx/SV Stablelock tripod) and don't seem to have an issue with either stiction or backlash. Panning is very smooth and I don't have an issue overrunning my target. I wonder if you might have an problem with a bad bearing surface??? Perhaps you might want to contact Larry at UA and describe the problem--maybe he'd have a solution for you. Or perhaps someone else here has experienced the problem and has a fix for you.
Bummer, as this certainly seems to be a nice mount at least in my experience...
Posted 29 March 2012 - 11:42 AM
Posted 29 March 2012 - 12:37 PM
Posted 29 March 2012 - 12:56 PM
Posted 29 March 2012 - 12:57 PM
I should also add the Unistar was bought used or "broken in".
Posted 29 March 2012 - 01:00 PM
I wonder if you might have an problem with a bad bearing surface???
That would be my guess as well. Fortunately, this is a very easy (and inexpensive) thing to fix. I'd definitely give Larry at UA a call.
Posted 29 March 2012 - 01:03 PM
Any you guys are using, say, 200x or higher power and do not experience any stiction, backlash or overruns??
I usually don't go much above 200x with any of my refractors (mainly due to atmospheric limitations), but have not noticed any of the issues you mentioned. Getting the scope perfectly balanced is key, however, in minimizing the likelihood of these problems.
Posted 29 March 2012 - 01:09 PM
I found the simple answer was to put a needle thrust bearing between the tension knob and the upright arm of the mount. This took all the torque off the knob/nut and put it onto the teflon bearing surface where it belongs. Alt motions are smooth and predictable with the bearing in place.
This is the thrust bearing I used:
I'm very happy with the results. Smooth even at 300x.
Posted 29 March 2012 - 02:53 PM
Posted 29 March 2012 - 03:04 PM
Don't know why Larry doesn't use a thrust bearing in the first place; it does a great job of putting the frictional load where it belongs.
Posted 29 March 2012 - 07:12 PM
Photos of bearing on alt axle and complete knob/bearing assy as used.
Posted 29 March 2012 - 07:15 PM
Posted 29 March 2012 - 07:24 PM
Posted 30 March 2012 - 08:12 PM
It looks like you removed the teflon bearing on this bolt. Yes?
Posted 30 March 2012 - 10:23 PM
Rich, quite honestly, it seems to me that that would eliminate all tension and your scope would be free-floating in the alt axis. No?
It looks like you removed the teflon bearing on this bolt. Yes?
Turning the knob essentially tightens a nut [inside the knob] on the threaded shaft that runs through to the plate where you attach your scope. [actually the knob itself may in fact be a solid piece with a threaded center hole]. The essential friction/tension is on the larger teflon spacer on the scope side of the mount. The roller bearing reduces the non-essential friction on the knob side which often causes the knob/nut to back off the threaded shaft when the scope is moved up and down on the Altitude axis.
I understand that my explanation leaves room for further clarification so I hope someone else gives their version. -Tim
Posted 30 March 2012 - 11:05 PM
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.
Edit: Tim, upon seeing your post above, you explained it well!
Posted 18 March 2013 - 12:34 AM
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.
Posted 18 March 2013 - 11:02 AM
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.
Posted 20 March 2013 - 12:45 AM
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?
Posted 20 March 2013 - 10:10 AM