18 replies to this topic

[Kasmos]

Yesterday was one of those days when a small unplanned side project turns into a overly time consuming project.

 

I recently purchased an incomplete 9TE from the sixties and during initial testing I found the focuser was way too stiff making it almost impossible to use.

 

The telescope is from about 1965 and showed little use and because of that the grease had turned to a very stiff goo.

 

I took it apart, cleaned everything, and regreased it using multi-purpose grease but afterwards the drawtube seemed looser with more annoying up and down play (droop).

It had some play before the re-grease but it wasn't quite as noticeable.

 

I was surprised to find these two shims under the axle of the pinion. I've taken a couple of these focusers apart and don't remember ever seeing them.

They appear to have been made from a scrap of a ID badge. It looks like it says Quality on one of them. 

 

Since one was almost cracked in half, I made two new ones from an aluminum soda can which looks to be about the same thickness.

 

This is before being re-greased for the second time. After this photo I bent (flared), the edges of the shims a bit outward to mimic how the originals first appeared.

I did this since it might help them stay in place.

 

To help with the drawtube's looseness/roop, I found there was just enough room for a strip of blue tape. The chromed draw tube must be a hair thinner from polishing on its outer end as I could feel the difference when inserting it in the housing. To take up a bit more slack at the outer end I put another small strip of blue tape under that end of tape.

 

This time I re-greased it with heavy-duty grease and it feels much better. There's a still a tiny bit of droop/play in the tube and there might be enough room for two complete strips of tape, but it's fine for now. Stickier grease would likely help the feel too.

 

I'm sure these focusers vary in fit and smoothness. Another I have feels much smoother, but it still has the original grease and I'm going to leave it. I'm probably expecting too much from it since these were pretty much low end products.

 

That said, what's been your experience with these focusers? Have any of you ever found shims like those above?

 

p.s.  I read that Chuck H. had found that some of the older and better focusers had lead shims.

Edited by Kasmos, 15 April 2019 - 03:58 PM.

[konrad]

I had a 7Te and a 10TE as well as a 4Vte  none had any shims only the spring clip , but as I was not the original owner perhaps they were removed at some stage

[DMala]

Yes sometimes you find them, sometimes you don't.

[Tenacious]

Nice job finessing the fit of the tube to the focuser!

 

I have a Tasco 6TE-5 (50mm x 600mm, circle T) with the same focuser design that I use for outreach.   Unfortunately, my rack is made of a soft pot-metal that slowly bends away from the pinion.

 

Mine didn't have shims.    I like your use of soda can aluminum.  Have to try that.

[Kasmos]

Nice job finessing the fit of the tube to the focuser!

 

I have a Tasco 6TE-5 (50mm x 600mm, circle T) with the same focuser design that I use for outreach.   Unfortunately, my rack is made of a soft pot-metal that slowly bends away from the pinion.

 

Mine didn't have shims.    I like your use of soda can aluminum.  Have to try that.

Thanks.

 

To be honest it could still use some of that original gooey grease to make it feel even better. This one has that pot metal rack and I noticed it's not installed perfectly straight. That might be why it feels a little weird (gritty), at each end of its travel, but it's probably because they bend away from the pinion in the middle and are tighter at the ends. I have what's left of one that broke, so I'm a bit paranoid about these types with their unsupported racks.

[Chuck Hards]

 

 I read that Chuck H. had found that some of the older and better focusers had lead shims.

Lead is actually an excellent bearing material for low-speed applications, used before Babbitt metals were developed or where the structure of Babbitt isn't needed.  I've since found a lead liner in a Japanese EQ mount, in addition to the focusers.  I've still got quite a bit of the thin sheet lead available, PM me if you need some.  It really smooths and tightens some focusers I've used it on.

[Kasmos]

Lead is actually an excellent bearing material for low-speed applications, used before Babbitt metals were developed or where the structure of Babbitt isn't needed.  I've since found a lead liner in a Japanese EQ mount, in addition to the focusers.  I've still got quite a bit of the thin sheet lead available, PM me if you need some.  It really smooths and tightens some focusers I've used it on.

Chuck, I can understand how the softness of lead would make it a great material for that. In the case of this Tasco, since it's seems that they all didn't have shims, I'm thinking they were sometimes used when the assembler thought the machining for the pinion recesses were too deep. 

[RRMichigan]

When I "rebuilt" a wobbly focuser on a Meade 395, I found the three shims inside were originally glued in but worn thin and crumbling. And for the life of me, they looked to be made of thin strips of bamboo...yes, Bamboo! Well, you know what they say. When in China, do as the Chinese do. I replaced them with cut strips of very thin plastic and lubed them. It took care of the slop and the focuser moves in and out smooth, but requires more force than usual to turn the knobs, but it causes no wear problems with the rack & pinion. Perhaps the plastic I used was a tad too thick. I did use the scope all last year with no problems, but I believe I'll have to revisit this focuser and try again.

Edited by RRMichigan, 17 February 2021 - 03:29 PM.

[Paul Sweeney]

Mine is from the early 80s, and it has no shims. It is nice and tight, virtually no image shift. Much better than the focusers on my Chinese refractors.

[Kasmos]

Since I still wasn't happy with it, I worked on mine again since this thread was posted and removed the pinion shims and relined the housing with tape. It still doesn't feel that smooth while focusing. I have another scope with the same type of focuser that's really smooth. It doesn't have shims but the housing has a cloth fabric (original to it), to take up slack for the rack tube. Since it's on a lousy cutdown f/400mm scope I may swap them.

[mclerran82]

I recently made some adjustments to my 10TE focuser as it had a little bit of play and I was trying to cut down on potential sources of vibration. My pinion had no shims installed there but there were three hard paper or cardboard shims that the focuser tube rides on.

 

I applied a layer of adhesive backed Teflon tape to each cardstock shim. I first used the next thickness up that McMaster Carr sells which worked but was a little stiff to operate. I also greased the rack and pinion with Mobil 33 grease. 
 

The focuser is now plenty smooth with no play.

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[blakestree]

I'm about to break my Swift 839 focuser down, to clean and regrease. I think I'm gonna try white lithium grease. Is that a bad idea?

[Kasmos]

I'm about to break my Swift 839 focuser down, to clean and regrease. I think I'm gonna try white lithium grease. Is that a bad idea?

Probably not. Many in this forum use it and I doubt it's hurt anything. IMO, just about any grease will work in a well machined rack and pinion focuser. Thick and sticky types are often used in focusers that have loose tolerances to improve their feel. That shouldn't be the case with a Swift. I don't remember ever doing anything to mine and it feels good. My personal peeve with White Lithium is that it sometimes seems runny and I dislike how it yellows with age.

 

One unscientific rule of thumb I go by, if a grease smells, don't use it, as it's probably more likely to be out gasing.

[blakestree]

Awesome, thanks for your advice!

[blakestree]

 

 

One unscientific rule of thumb I go by, if a grease smells, don't use it, as it's probably more likely to be out gasing.

 

I do have some bearing grease, too. But, it may well exhibit the gas off issue you suggest.

[Kasmos]

I do have some bearing grease, too. But, it may well exhibit the gas off issue you suggest.

I've used bearing grease many times but usually the plain old amber type since the red stuff I have smells. Keep in mind out gassing may not pose too much of a problem with only a tiny bit being used at the focuser. The bigger problem is when its used in a sealed system like a SCT. 

 

I say use what you have, so If you have white lithium don't let what I said earlier stop you.

Edited by Kasmos, 21 February 2021 - 03:05 PM.

[blakestree]

I've used bearing grease many times but usually the plain old amber type since the red stuff I have smells. Keep in mind out gassing may not pose too much of a problem with only a tiny bit being used at the focuser. The bigger problem is when its used in a sealed system like a SCT. 

 

I say use what you have, so If you have white lithium don't let what I said earlier stop you.

Mine is the translucent amber type. Maybe I should experiment with which has the best feel.

[Kasmos]

Mine is the translucent amber type. Maybe I should experiment with which has the best feel.

I might be wrong but you probably won't be able to feel any difference. Remember you don't need much, just so it's not dry. I also forgot to mention that I and another member have even used petroleum jelly!

[blakestree]

I also forgot to mention that I and another member have even used petroleum jelly!

Hey, that's between you and your friend. What you do in your own time, and all.