?

Greg,

?

If by worm clearances you mean the mesh spacing as indicated by the position of the bearing blocks relative to some (unknown) reference point the answer is No.

?

It is a “feel it and adjust” job, where that means do a preliminary adjustment, then rotate the worm by hand (motors off) until you find the high spot on the worm wheel (as indicated by increased resistance to rotation of the worm) and then back it off a bit. No worm wheel is perfect, so there is always some radial variance in the teeth (a consequence of the center of rotation not being exactly the center of the gear tooth pattern + variance in the machining of the individual gears.

?

So if you just adjust the mesh to be perfect at an arbitrary position on the gear you are almost guaranteed to be too tight at some other point on the worm wheel.

?

There are quality ratings for worm gears (AGMA – American Gear Manufacturers Association, just Google on that) in general that govern the tooth-to-tooth variance and the total variance in the teeth but that just indicates ‘fitness for use’, not a position for the worm itself. Sure, as a function of the tooth pitch and worm diameter there will be a nominal distance for the worm relative to the center of the worm wheel, modified by the tooth-to-tooth variance. But that is just used for designing a nominal position for the worm plus enough adjustment range to allow the hand adjustment to be made.

?

Byer’s drives (the old classics, still available on Ebay) used to be sold with an AGMA rating but most mount manufacturers don’t give the ratings for their worm/worm wheel pairs.

?

Power transmission systems (lots more torque and higher speeds) are a different kettle of fish, of course.

?

Even if one were to do a great job of adjusting the mesh (as determined by the hand adjustment and then verified by actual tracking/guiding tests) and then scribed the location of the bearing blocks onto the mounting plate, I would still only use that as a starting point the next time the gears needed to be tweaked.

?

Things like adjusting worm mesh is why good assemblers are valuable. Such folks are usually referred to as possessing ‘golden hands’ or just mechanical sensibilities.

?

Cheers,

?

Mark Christensen

?

8. Strictly speaking, clutch knob force should not affect the worm to ring space, because the ring gear runs on the top large flat (incompressible) needle bearing under it, and the worm is also mounted on an immobile part.? ? ?But some people have seen this happen.? ?Eric Chesak has written about this and determined the possible mechanical causes.

I have been trying to optimize the worm / spur ring gear alignment. What is being referenced above is that
the Worm block is too high : when closely pressed to the ring it Lifts the Ring above the upper thrust bearing.

The gear cuts in the ring are very shallow .. a 0.001 of 'vertical' misalignment can cause the worm-ring to jam.

SO, when the clutch is tightened, it pulls the upper shaft downward ,presses the ring into the upper thrust bearing and jams or tightens up the worm-ring.

I found I needed to Shim Up the Ring - Thrust bearing.spacing by 0.007" on the Dec and 0.005" on RA.. I can get very tight coupling and no binding and no lockup upon adjusting the clutch.

- Alex
Winter Springs Fla

?

a-Pettit- JR & Michael Herman,

? ? ? ? ? ?I discovered the issue about mismatched centers between the worm gears and worms, on my G11 mount, while seeking ways to optimize the tracking of it. At that time I posted an inquiry about the issue on this forum around a year ago.? At that time the majority opinion from the feedback I got was that the effect of the misalignment was negligible including Franck Vlbousquet of Ovision. ?

? ? ? ? ? ? ? The primary opinion stating the vertical centering was important for optimum tracking, was from Ed Byers who’s knowledge of worm drives is without question an authority on the subject.

? ? ? ? ? ? ?The vertical alignment of the drives on my G11 mount, if I remember correctly, was .005” on one axis and .009” on the other. ? For shim material, I found an aluminum Pepsi can is about .004” thick and with some searching I found another aluminum can to be .0085”. ? ?After cutting these into the proper sized disks and installing them, I felt they helped some but this alone did not eliminate all mechanical error from the G11 Mount.

? ? ? aruckle ? ? ? ??

? ? ? ? ? ??

?

Hello Arukle,

Thanks for the information.?
I am not sure this will improve Any tracking issues. What it will do is engage more of the gearing surfaces.
This distributes the contact load and may thus smooth? out the smaller 'second to second'
tracking? imperfections.

I used the shim set as 'feeler gauges'? I stepped up in 0.001" increments .. I found one spacing where I could not,
or barely lift the ring-spur gear, and going 0.001" beyond that caused lockup when I pushed the ring down on the
thrust bearing group. That was my indicator of correct spacing : If I could press down hard on the ring upon the
thrust bearing and maintain smoothness in the feeling via the added? manually turned worm-shaft knob,
I knew I? had hit the best spacing.

When adjusting the worm-block set, it is imperative as others have stated, to keep firm pressure on the
right block to press it against the 'fixed' left block to eliminate worm shaft play. I used the cover plate
to align the blocks square to each other, but there is a few degrees of rotation alignment freedom in the
bearings, so you can lock the left and make small adjustments to the right block without issue.

Alex

?

Michael,

I used a long 10-32 screw to hold the housing and a Bernzomatic torch to heat it and the bearing
just fell out, then let the housing air cool.

Don

----- Original Message -----
From: "Michael Herman mherman346@... [Losmandy_users]" <Losmandy_users@yahoogroups.com>
To: <Losmandy_users@yahoogroups.com>
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

?

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.??

I put some aluminum tape around the threads of a long 1/4" hex head bolt. First lap, sticky side against the thread,
then folded back for another lap sticky side out.? Jam into bearing. Put Block into vice, crescent wrench on the
far end of the bolt at the hex head ; Wack Wrench Once With Hammer = fast extraction !
?(I would never use the bearing again, but no damage to the housing )

Alex