32 replies to this topic

[hboswell]

I've been working on my Sears 6339-a getting it ready to go out under the stars. Everything looks good at this point except - the RA seems to be locked. I can move it with the slow-motion control, but no matter how loose I make the RA clamp lever, I can't move the mount in RA. Declination is fine, but I can only move RA with the slow-mo cable. Is there a lock somewhere on this mount that I'm missing?

 

Thanks,

Harry

[LPHawaii]

Did you try removing the gear assy and then trying to turn the RA axis?  U need to determine if it is the gear or the RA shaft causing the problem.  If both move freely you need to adjust the RA gear assy.  It could be cause by the gears not meshing correctly or the gear assy is too tight.

[Garyth64]

The lever pushes down on a piece of brass that has a V-shape at the bottom.  It fits into a V-shape ring.  Some times that piece of brass gets stuck.

 

It may be required to take the cover with the 5 bolts off so you can see the piece of brass.

 

You may need another section of brass, and the V-shape of the ring may be marred.

 

This is actually quite common. Here a cross-section drawing of what I'm talking about:

 

Edited by Garyth64, 26 February 2025 - 08:45 PM.

[hboswell]

Thanks, I'll check these out in the morning.

 

Harry

[deSitter]

I've been working on my Sears 6339-a getting it ready to go out under the stars. Everything looks good at this point except - the RA seems to be locked. I can move it with the slow-motion control, but no matter how loose I make the RA clamp lever, I can't move the mount in RA. Declination is fine, but I can only move RA with the slow-mo cable. Is there a lock somewhere on this mount that I'm missing?

 

Thanks,

Harry

I suspect the wedge thingy in the above post has been driven so hard into the brake ring that it is frozen. This was a clever design, unfortunately realized with non-ideal metals. If yours is stuck, be extremely careful trying to unstick it. It is very easy to break the brake ring and then the mount will be useless. Take off the bat and nut with 4 threaded holes and shine a bright light down into the hole in the RA cap. You should see the top of the brass wedgie.

 

Remove the black cast aluminum cap by removing all 4 screws and prying it off with a plastic knife of the like. There are a couple of fishpaper brick-colored gaskets under it. Remove those. You'll see the brass RA drive gear and the pot metal brake ring. One side of the ring has a threaded hole, and directly opposite is the wedge, which pushes the ring into the inner surface of the RA gear by splaying it outward. I cannot overemphasize how fragile is the pot metal brake ring. Do not bend it out of plane. Once everything is out, put the tip of a screwdriver into the threaded hole of the brake ring and push on it tangentially to the circumference of the ring to verify that it is free. If not, don't do anything else before returning here.

 

-drl

Edited by deSitter, 26 February 2025 - 11:22 PM.

[hboswell]

Did you try removing the gear assy and then trying to turn the RA axis?  U need to determine if it is the gear or the RA shaft causing the problem.  If both move freely you need to adjust the RA gear assy.  It could be cause by the gears not meshing correctly or the gear assy is too tight.

This afternoon I took the cover plate off. With the plate gone the RA moves freely and smoothly. Put a single screw in and it won't move except for maybe a quarter inch in either direction, which is the same thing I've been hitting with the cover fully assembled. I don't know if the red sleeve (see attached photo) is interfering. I've never taken an eq mount apart before so I don't know what I expected it to look like.

 

Harry

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[Garyth64]

In your photo, the little brass wedge is shown.  Can you remove  it?

 

If nothing is moving, then I'd suspect the brass wedge is still tight into the ring. The ring pushes against the ring gear.

 

At this point, do not have the telescope or any counter weight on the mount.

 

Carefully remove the red  gasket to get it out of the way.  Everything should be turning smoothly.

 

I do have a extra 6339a mount that's partially in parts.  I will use it to work this thru with you.  I will get it out, and get it to the same picture that you show, then we can go from there.  I'll take pictures too.

Edited by Garyth64, 01 March 2025 - 07:44 PM.

[Garyth64]

So here is my mount like yours is.  I removed the gasket (which is a clear plastic one I made), and you can see the brass wedge.

 

 

At this point, the  RA axis turns very easily.  This is why the scope and counter weights should be removed.  You'd have no control over them.

 

Also, the yoke part of the mount should be able to lift off and be separated from the rest of the mount attached to the tripod.  You don't have to lift it off at this time.

 

If you think the mount needs cleaning, lift the yoke off and it will look like this:

 

 

You can see that the brass ring gear moves up and down, but it will not fall out.  The worm gear is holding it in place. The split ring can easily be removed, but do it carefully.

If you want to clean things more, you have to loosen up the worm or take it out.  Caution, the worm gear, if it has never been messed with, may be set in the correct position as it came from the factory.  On both sides of the worm gear the are eccentric adjusters or cams held in place by two set screws for each.  The turning of those adjusters positions the worm gear against the ring gear.  It is not fun to play with, and it drives me nuts trying to get it right.  Try to remember or record the position of each cam when you go to put it all back together.

But you may want to clean the ring gear and the worm gear and replace the old grease.

 

Another guy here on CN did a thread on repairing and adjusting these mounts.  On first try I couldn't find it, but I'll look again.

 

I found it.  Here is the other thread.  It's worth a look:

 

https://www.cloudyni...sco-3-eq-mount/

 

And now that I've looked thru that thread, Preston explains things a lot better.

Edited by Garyth64, 02 March 2025 - 08:34 AM.

[deSitter]

This afternoon I took the cover plate off. With the plate gone the RA moves freely and smoothly. Put a single screw in and it won't move except for maybe a quarter inch in either direction, which is the same thing I've been hitting with the cover fully assembled. I don't know if the red sleeve (see attached photo) is interfering. I've never taken an eq mount apart before so I don't know what I expected it to look like.

 

Harry

The design of this mount is sort of sui generis, It is a very good mount IMO. I have 2 of them Sears/SYW 6344, Sears/AO 6335 version 2, which is the same scope as the 6339/a models but in a different finish. Garyth64 knows this mount like his hand, he'll fix you up.

 

-drl

Edited by deSitter, 02 March 2025 - 12:10 AM.

[deSitter]

So here is my mount like yours is.  I removed the gasket (which is a clear plastic one I made), and you can see the brass wedge.

 

6339 mount repair 01.jpg

 

At this point, the  RA axis turns very easily.  This is why the scope and counter weights should be removed.  You'd have no control over them.

 

Also, the yoke part of the mount should be able to lift off and be separated from the rest of the mount attached to the tripod.  You don't have to lift it off at this time.

 

If you think the mount needs cleaning, lift the yoke off and it will look like this:

 

6339 mount repair 02.jpg

 

You can see that the brass ring gear moves up and down, but it will not fall out.  The worm gear is holding it in place. The split ring can easily be removed, but do it carefully.

If you want to clean things more, you have to loosen up the worm or take it out.  Caution, the worm gear, if it has never been messed with, may be set in the correct position as it came from the factory.  On both sides of the worm gear the are eccentric adjusters or cams held in place by two set screws for each.  The turning of those adjusters positions the worm gear against the ring gear.  It is not fun to play with, and it drives me nuts trying to get it right.  Try to remember or record the position of each cam when you go to put it all back together.

But you may what to clean the ring gear and the worm gear to clean clean up and replace the old grease.

 

Another guy here on CN did a thread on repairing and adjusting these mounts.  On first try I couldn't find it, but I'll look again.

 

You may also find some good information here:

 

https://www.cloudyni...sco-3-eq-mount/

 

And now that I've looks thru that post, Preston explains things a lot better.

So I'll try to summarize, maybe it will help.

 

The brass circle you see looking down the RA axis is the top of a large brass torus, sort of like a tambourine with no canvas. The entire outside circumference is inscribed with a gear, which is driven by the slo-mo control (at the bottom). The inner ring is the brake - you tighten down the lock and it shoves the wedge into the brake ring and splays it outward, so that it becomes bound to the brass ring and can be driven by it. Thus the main bearing surface is between the mount casting and the inside of the brass ring gear. There should not be excessive lubrication where the brake ting contacts the brass gear. If you cannot move the scope freely when unlocked, the brake ring must be bound to the brass gear. Getting it unstuck risks breaking the brake where it flexes, opposite the brass wedge.

 

So the first task is to remove the brass wedge and see if you can free the brake with very gentle nudging/persuading OPPOSITE the brass wedge - where the brake flex happens. This brake is very fragile - you do not want to be pushing downward on it near the wedge!

 

If the brake cannot be unstuck with simple methods, the entire brass gear and frozen brake must be extracted from the DEC casting.

 

-drl

[hboswell]

As an aside - am I right in thinking that this mount was/is a much better equatorial mount than the inexpensive mounts (CG-1, CG-2, CG-3) we have been seeing for the past 30-40 years?

 

Harry

[hboswell]

I was able to remove the brass wedge. It offered a little resistance but not too much. What's underneath looks pretty gunky to my inexperienced eye, what do you guys think? Should it look like this?

 

 

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[Bomber Bob]

Is that corrosion or hardened grease down in the Vee channel??  

 

It'll be worth your time & effort to disassemble, clean, & re-lube.  Mine was slicker than... well, moved with near-zero friction afterwards, and the clutch engaged / released like brand new...

 

 

BIF:  NOTE the microscopic AO Mark on the slo-mo "cube" (1st pic, upper right side).  Why There??

Edited by Bomber Bob, 02 March 2025 - 11:21 AM.

[Garyth64]

hboswell,

no, it should not look like that (but it is typical for what would happen over 50+ years.  The  little brass wedge should have been very easy to remove.

 

Does that section rotate now?  Or is it still stuck.  I think it is still stuck and probably "glued" in place with the old grease.

 

IMO, the only thing to do now is to disassemble the mount and clean out the old hardened grease and re-lube it all.  I would take the mount off the tripod and head to work bench.

Edited by Garyth64, 02 March 2025 - 11:17 AM.

[deSitter]

hboswell,

no, it should not look like that (but it is typical for what would happen over 50+ years.  The  little brass wedge should have been very easy to remove.

 

Does that section rotate now?  Or is it still stuck.  I think it is still stuck and probably "glued" in place with the old grease.

 

IMO, the only thing to do now is to disassemble the mount and clean out the old hardened grease and re-lube it all.  I would take the mount off the tripod and head to work bench.

Agreed. And to hboswell - be careful of the black finish on the mount - it is paint. Don't get acetone or strong Goo-Gone on it. Use mineral spirits where there is paint, and save the strong stuff for the metal parts.

 

-drl

[deSitter]

Is that corrosion or hardened grease down in the Vee channel??  

 

It'll be worth your time & effort to disassemble, clean, & re-lube.  Mine was slicker than... well, moved with near-zero friction afterwards, and the clutch engaged / released like brand new...

 

S06 - Parts After Cleaning 1.jpg S07 - Relube Polar Axis 1.jpg

 

BIF:  NOTE the microscopic AO Mark on the slo-mo "cube" (1st pic, upper right side).  Why There??

Modesty? On the f/20 SPI of dblstar that tiny mark is on a shaft collar! My AO mounts also have the stamp on the DEC tangent block like here. It is not on the similar, version 2 of the mount that came with the Sears/SYW 6344. I call these the "Cepheus" version 1 (4 screws in the RA plate + lock nut looks like the constellation Cepheus) and the "Crux" version 2 (3 screws + lock nut looks like Crux).

 

-drl

Edited by deSitter, 02 March 2025 - 02:03 PM.

[Bomber Bob]

BIF2:  The trickiest part of re-assembly for me was getting the best Mesh of that asymmetrical Polar  Axis gearing -- took a couple of tries.  Once done, everything worked better, including the motor drive's tracking:

 

 

My first expensive Classic.  It was a Wise Choice...

[hboswell]

Man I would love to have a pedestal like that - I'm 6'5" and even a fully extended tripod is a challenge for most things!

 

Harry

[deSitter]

Man I would love to have a pedestal like that - I'm 6'5" and even a fully extended tripod is a challenge for most things!

 

Harry

That is the Sears 6336 - like the 6335 (same as the 6339) but with a pedestal and a small 6x30mm or 5x24mm finder in addition to the 12x40mm finder common to the 6335.

 

Tasco also made the 15TE, again with the same OTA as the 6339 but on a pier.

 

-drl

[hboswell]

OK, at this point I'm a little confused about how to disassemble the mount - what's the next step?

 

Harry

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[deSitter]

OK, at this point I'm a little confused about how to disassemble the mount - what's the next step?

 

Harry

Preston's how-to posted above has detailed information on this exact mount.

 

To remove the drum and stuck brake, you must first disengage the worm gear that drives the slo-mo in RA. That worm is supported on each end by an eccentric bearing made of chromed steel. The shaft of the bearing is off center. This means you can spin the bearing in its mount in the casting and so lower the worm gear out of the way. You do NOT need to remove the worm assembly - just loosen the set screws and spin the bearing until the worm gear shaft is as far as possible away from the drum. The brass drum should then fall out.

 

Take close up pictures of each eccentric bearing so you will know where to position them when you reassemble.

 

Once the drum is out, you can work on freeing the brake ring from it.

 

-drl

Edited by deSitter, 07 March 2025 - 03:24 PM.

[Garyth64]

Look at my 2nd picture in #8, or the 2nd picture in #13.  Grab the yoke and lift it off.

 

If you want to remove the large brass ring gear, you have to loosen up the worm gear.   

Edited by Garyth64, 07 March 2025 - 02:41 PM.

[deSitter]

Preston's how-to posted above has detailed information on this exact mount.

 

To remove the drum and stuck brake, you must first disengage the worm gear that drives the slo-mo in RA. That worm is supported on each end by an eccentric bearing made of chromed steel. The shaft of the bearing is off center. This means you can spin the bearing in its mount in the casting and so lower the worm gear out of the way. You do NOT need to remove the worm assembly - just loosen the set screws and spin the bearing until the worm gear shaft is as far as possible away from the drum. The brass drum should then fall out.

 

Take close up pictures of each eccentric bearing so you will know where to position them when you reassemble.

 

Once the drum is out, you can work on freeing the brake ring from it.

 

-drl

Note - I do not explicitly remember if just lowering the worm is enough. It may actually be necessary to remove the worm assembly completely. That would be the "right" way to do it, but if you just want to get it going with minimal effort (a valid goal!) it would be better if that were not necessary. Don't ever force anything! If it doesn't come out easily, even if you have to fiddle around to find that configuration, never try to use force to "make it work". These are soft metals and fragile castings.

 

(edit - From the point of view of geometry, it should come out just by lowering the bearings. But the drum must come straight out without turning.)

 

Another note - reinstalling and adjusting the eccentric bearings is the weak point of this mount. It is incredibly finicky. The tiniest changes make an enormous difference. Don't worry about slop and backlash at first. Just get it back in one piece.

 

-drl

Edited by deSitter, 07 March 2025 - 03:43 PM.

[hboswell]

The next step decided to perform itself for me - I had the mount off the tripod and sitting on my workbench, and reached over to move it out of the way so I could set my 7" reflector there to replace the focuser, and when I picked the mount up it separated into two parts with a couple of gaskets falling out.  I guess at this point I might as well go on to the worm gear and clean it all up but - what should I use to clean all of this, and what should I replace the old grease with?

 

Thanks,

Harry

 

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[Garyth64]

The parts can be cleaned with alcohol or even WD40.  The old grease can be removed and replaced with almost any modern stuff.  

I have used Lube Gel with Teflon, it's good in all temps.  I also have some pink stuff that my dad had.  On some things, I  have used Lacquer thinner and Acetone, but with those you have to be careful around some paints.  When I clean parts I have them sitting in a aluminum pie pan.  I use tooth picks, tooth brushes, Q-tips, and a couple of rags.

 

That split ring can be easily removed.  Are there any marks in the V?  How does the brass wedge look?  The way those two items worked together, brass wedge could mar the split ring V.  And it may be trial and error to see if just cleaning will keep it from sticking and locking up the RA.  If it continues to stick, and not release.  There is a remedy that I have done, but we can get to that later.  It is different that what some other guys have done.

Edited by Garyth64, 08 March 2025 - 07:55 PM.