Losmandy gm8 worm adjustment

[Ramsay11 (Stephen)]

I have a new GM8 with Digital Drives, using a 120mm ED refractor for visual observation. I have experienced issues with play or slop in the DEC axis. An inquiry to Losmandy received a verbose reply "worm to worm gear setting" Basically, position the worm closer into the worm gear to reduce it. My question is, how close can it be positioned before it causes too much friction?
Secondly as the evening temperatures drop the RA worm seems to lose contact with the worm gear and the hand controller can't move the scope in RA but the motor is audibly working. I have adjusted the worm somewhat closer, but again the question, how close?
A suggestion was to set the distance between the worm blocks and the mount using an automotive feeler gauge which I have at my disposal but no mention of gauge thickness (distance of block from axis) A concern is "what is the right setting and proper methodology to resolve these issues"?
The Losmandy User group, to which I belong, appears to be dedicated to owners whose interests lay in astrophotography, reducing periodic error, etc. but nothing as mundane as my problem.
When one uses a long refractor, it places a polarized load on the mount versus a compact OTA, any play, particularly in DEC axis has an adverse effect, so what is an acceptable tolerance in this area?

Stephen

[Hagar (Doug)]

Hi Steven and welcome.

Sounds to me like the worms definitely need some adjustment. I have a G11 which has a similar setup.

As a general rule the worm should be positioned until you can just feel a tiny amount of movement between the worm and the gear. The next thing to check after setting the worm is that it allows the gear to drive completely around without any binding. With this adjustments made you should notice quite a difference in operation. Just try to keep everything square. Some use feeler guages to set the worm blocks square to the frame and gear.

[multiweb (Marc)]

Here's a quick run down that works for me:

1_ get the scope out and decouple the motor (oldham coupling) so you can turn the worm by hand.

2_ Take the worm cover off and loosen the two hex screws holding the end blocks so they can move/rotate.

3_ Squeeze both end blocks together (against the worm ends) so there's no play, and use the worm cover as atraverse to make sure the blocks are square and in-line.

4_ Mesh the worm against the gear and tighten up the end block on the gear box side. Then tighten the other one.

5_ Turn the wom by end feeling any hard spots across the whole circumference of the gear and note for tight spots. Release the meshing by moving the end block so it runs smoothly. Whenever you do that use the worm cover to square the end block before tightening it and make sure you also squeeze it against the worm.

That should get you in the ball park.

[JohnG (John)]

Hi

This may be of some help to you. About 2mm of side to side movement at the end of the Counter Weight Shaft is usually close.

Cheers

[[1ponders] (Paul)]

Originally Posted by multiweb

Here's a quick run down that works for me:

1_ get the scope out and decouple the motor (oldham coupling) so you can turn the worm by hand.

2_ Take the worm cover off and loosen the two hex screws holding the end blocks so they can move/rotate.

3_ Squeeze both end blocks together (against the worm ends) so there's no play, and use the worm cover as atraverse to make sure the blocks are square and in-line.

4_ Mesh the worm against the gear and tighten up the end block on the gear box side. Then tighten the other one.

5_ Turn the wom by end feeling any hard spots across the whole circumference of the gear and note for tight spots. Release the meshing by moving the end block so it runs smoothly. Whenever you do that use the worm cover to square the end block before tightening it and make sure you also squeeze it against the worm.

That should get you in the ball park.

Marc has described pretty well what i do as well. The only other thing you need apart from feeler gauges, worm cover, and allen key is about 2 other pairs of hands. You can do it on your own but a couple of extra hands to hold feeler gauge and worm cover goes a long way to making the adjustments less....... challenging

The only thing I do a bit different is I use a battery drill set to the lowest torque setting (or close to it). You need to be able to stop the chuck turning with a couple of fingers. I then put the coupler from the motor on the end of a reversed bit (or piece of rod if you have one the correct size) and use the drill to drive the worm. Works a treat and saves on the finger tips. You could do a way with the drill and turn it by hand but i prefer the precision of the torque setting on the drill. If you are going to try it by hand only use thumb and forefinger to turn the bit shaft.