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Question for UniStar Mount Owners

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#1 Dave Ponder

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Posted 29 March 2012 - 06:35 AM

I received the UniStar Deluxe Mount recently, but have some concerns how "smooth" its motions should be. I do balance my scope, an EON 120, but the motions mainly in altitude show "stick-tion" (if that is the right word). I constantly move past the object being viewed when trying to center it at higher powers (200x plus). There is some play in effect before the friction kicks in to hold the scope. I have tried to adjust the tension knob but if I tighten it enough to take out the play, it increses the stick-tion factor. From reviews I have read, I was expecting this mount to very smooth at high powers and not having to bob the scope up and down trying to keep the object in the field of view. Hope this all makes sense. How does your UniStar Mount perform with respect to its motions, sticky or smooth?
Thanks!

#2 Jeff Bennett

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Posted 29 March 2012 - 11:11 AM

I use a Unistar Deluxe with my SV115T and find it to be very smooth with virtually no play. I find that I can adjust the altitude friction from almost nothing to something a lot tighter and get the same smooth performance.

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.

Jeff Bennett

#3 Phil Frederick

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Posted 29 March 2012 - 11:24 AM

Dave,

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...

Phil

#4 Dave Ponder

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Posted 29 March 2012 - 11:42 AM

Any you guys are using, say, 200x or higher power and do not experience any stiction, backlash or overruns??
Much thanks,
Dave

#5 Jeff Bennett

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Posted 29 March 2012 - 12:37 PM

I routinely run my SV115T at 160X and sometimes at 228X (with 5 and 3.5mm XWs) On the Unistar with no backlash or sticking.

Jeff

#6 dscarpa

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Posted 29 March 2012 - 12:56 PM

I bought a Unistar for my heavy as a stock C11 C9.25 2 months ago. I'm having the same sticktion-backlash problem with both axis. I called Larry and he said the mount will get smoother after a breakin period. I've only used the mount a few times so that hasn't happened yet. My main taget now is Mars which is all about high power. I observed Mars once using the Unistar it was frustating to say the least. After Mars leaves the scene I'll breakout the Unistar. The Moon will make a good high power practice object given it's size. David

#7 Jim7728

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Posted 29 March 2012 - 12:57 PM

190x has been very manageable with my MN-66 and Unistar Deluxe/CG-5 tripod. Some settling occurs after tracking at that high power, but is acceptable to me. Key with any manual alt/az is good balance of the ota especially on the altitude axis which then requires that the tension knob be only snug , not tight which can lead to sticktion.

I should also add the Unistar was bought used or "broken in". :grin:

#8 Scott in NC

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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.

#9 Scott in NC

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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??
Much thanks,
Dave


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.

#10 Rich V.

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Posted 29 March 2012 - 01:09 PM

I've run into some tension difficulties on the alt axis with my Unistar Super 8/ TMB 130. It seems to me that too much torque is being transferred to the interface between the tension knob/nylock nut and the axle bushing in the upright. This works some slop into the system eventually as the nylock wears making a "dead spot" in the friction. Sometimes there is sufficient torque to even loosen the tension knob when moving the scope while set at higher friction levels.

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:

http://www.vxb.com/p.../Thrust/Kit8670

I'm very happy with the results. Smooth even at 300x.

Rich

#11 dscarpa

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Posted 29 March 2012 - 02:53 PM

Thanks for the tip!. It can't hurt to get a bearing for both axis. David

#12 Rich V.

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Posted 29 March 2012 - 03:04 PM

The bearings are inexpensive but there's an approx. $5 shipping fee. I bought several bearings since the shipping was a fixed price anyhow. Got an extra for a friend's Unistar also. I just smeared some quality synthetic/teflon bicycle bearing grease on the bearing when when I put the stack together.

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.

Rich

#13 zawijava

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Posted 29 March 2012 - 06:38 PM


This is the thrust bearing I used:

http://www.vxb.com/p.../Thrust/Kit8670

I'm very happy with the results. Smooth even at 300x.

Rich


Any chance you've got a pic of that bearing installed? thanks, Tim

#14 Rich V.

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Posted 29 March 2012 - 07:12 PM

The bearing just stacks behind the tension knob; it's thin like three washers so you hardly know it's there.

Photos of bearing on alt axle and complete knob/bearing assy as used.

Rich

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#15 Rich V.

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Posted 29 March 2012 - 07:15 PM

Bearing in normal use; hidden under the tension knob:

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#16 Scott in NC

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Posted 29 March 2012 - 07:24 PM

Great tip, Rich, and thanks for the illustrations! I'm going to file this post away for future use, in case my Teflon bearings ever wear out.

#17 zawijava

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Posted 30 March 2012 - 03:01 PM

thanks Rich, great tip...think I'll give it a try.

Tim

#18 Goodchild

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Posted 30 March 2012 - 08:12 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?

#19 coopman

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Posted 30 March 2012 - 08:30 PM

I was about to ask the same question myself.

#20 zawijava

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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

#21 Rich V.

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Posted 30 March 2012 - 11:05 PM

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!

#22 Gordon Rayner

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Posted 18 March 2013 - 12:34 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.

#23 Rich V.

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Posted 18 March 2013 - 11:02 AM

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

#24 Gordon Rayner

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Posted 20 March 2013 - 12:45 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?

#25 Rich V.

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Posted 20 March 2013 - 10:10 AM

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

Rich






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