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----- Original Message -----
From: "Michael Herman mherman346@... [Losmandy_users]" <Losmandy_users@...>
To: <Losmandy_users@...>
Sent: Sunday, January 28, 2018 9:29 PM
Subject: Re: [Losmandy_users] Re: GM8 DEC Clearances


That is ...interesting. The companies making the mounts consider slight
off center alignment acceptable... in the Losmandy case this could be
because the ring and worm are not (advised to be ) forced to touch. That's
why many folks put a hanging weight wrapped cord around RA and maybe DEC to
have the teeth mesh on only one side of the worm thread.

Other mount systems use some type of spring or the elastic properties of
the materials to force the ring and worm into tight contact. The Orion
Atlas/Syntax EQ6 uses the aluminum housing as a kind of spring for this.
In that situation, you must shim under the time gear to put the ring gear
thread center at the same height as the worm axis center...at least within
the tolerance of the shims they provide.

Now we have the Pepsi Can solution of shimming! Thats a pretty nice way of
recycling!

.....

Related to all this vertical spacing, you still have to get the worm and
it's coupling not to shift side to side. I had this trouble til today on
a used system I got last week.

I got a 1998 vintage used G11 last week. It was reported by the previous
owner to not able to get the worms to mesh consistently around the 360
degree turn of the ring. it would either be too loose (too much
hysteresis/time lag) or too tight (stall from jamming). He gave up and
sold the mount.

I got these fixed over the last few days. Here were the problems:

The DEC used 2 separated worm bearing blocks -- standard for the Losmandy
G11. The worm was able to slide side to side along its axis maybe 1/8 inch
or so...you could see the movement. I removed the far worm bearing (see
the notes at the end of this) and installed a single Belleville washer. I
also had to sandpaper down the OD of the bearing so it could slide with
lubricant along the cylinder of the block. The black blocks are anodized
so their surfaces are essentially sapphire hardness...those cannot be
sanded. It took about 20 minutes of sanding with grit 200 sandpaper to get
the OD small enough to slide in the block. Then I reinstalled that block
on the DEC axis, forcing the worm toward the gearbox. Now that DEC worm
has zero side movement, and then it was possible to push the worm touching
the ring...no more rotational hysteresis...no more time lag, and no more
jams either.
The DEC Oldham couper was also far out of axial center line, and that
proved hard to get coaxial. I had to completely loosen the Oldham coupler
both metal ends and when that was free, I did find a way to bolt the
gearbox so the gearbox shaft axis matched the worm axis. Then I locked
down the Oldham ends. So the DEC seems fixed.

The RA was a different matter. That had an OPW but same trouble....worm
side movement. This time I put a pair of face to face Belleville washers
into the far (silver color...stainless?) bearing block. Same work to
polish down the outer bearing OD to slide with lube.

But this OPW also had a "Ruland" type coupler, not the stock Oldham
coupler. The Ruland coupler design allowed it to flex, but I could not
tell visually if the gearbox shaft lined up with the worm. So I replaced
the Ruland with a (long version!!!) Oldham coupler. Then I lined those up
and...voila. I thought I was done.

Not so. The double back to back Belleville washers pushed out the far worm
block so the resulting wide space between the mounting blocks did not allow
the worm to be pushed inward toward the ring gear. I could not push the
worm to touch the RA ring gear....still lots of gap and time lag and
hysteresis. So I removed the OPW, and loosened the bolts holding the far
block. By pressing in the far worm block strongly by hand, the double
Belleville washers squashed down to bring the far block close enough to the
gearbox so now I was able to get the worm to touch the ring gear.

Now..I have full rotation of the RA and DEC...no jams, stalls, lags, no
hysteresis. (When it gets cold tonight, we'll see if I can still make that
claim.) I plan to run a PE test tonight and see what the results
are....the sky here is too milky and moonlight too severe for any other
fun. I'm hoping the mount will match my older CG11 with about 0.9 arcsec
RMS PE.

P.S....getting the far bearing out:
My idea of making a 10-24 size bolt+nut+ heavy gauge steel wire into a
bearing puller failed to get the bearing out of the far, black, DEC bearing
block. I failed with other ideas, but this worked: I used steel wood
nails, with shaft diameter about 3/16 inch, and bent the ends into an L
shape. The end of the L was about 3/16 enough to get into the 1/4 ID of
the bearing. I jammed in 2 of these hooked nails. The nail heads were
then held in a vice, and I was able to gently tap on the block with a sand
filled plastic mallet and knock the block off the bearing. Not elegant but
at least it did work.

All the best, and hope these notes help the group....

Michael