help me get my eq5 to drive nicely

[Starkler (Geoff)]

After having bought Mortons ED115S (very nice scope it is too), I have purchased and fitted a set of drive motors for the eq5 mount I had tucked away.

I'm now plagued with backlash with this drive. The dec is much worse than the ra. With 8x speed selected, there is a good 6 seconds worth of backlash if I change directions in dec.

After much mucking around this afternoon it became apparent that upon applying torque to the worm gear, it skews off "sideways" for a bit before the slack is taken up and the mount starts moving. what this means is that the worm gear shaft can slop perpendicular to its axis under tension.

I ran out of daylight when i discovered this. There is no end to end slop apparent. Does anyone know the fix?

[Omaroo (Chris Malikoff)]

Geoff - have you tried to adjust the slop out by fiddling with the centre set screw (in between the two Allen-head bolts that keep the worm assembly on)? It adjusts the tension between the worm and wheel rack. Have you also tried to reverse the head 180 degrees to see if the other side of the worm wheel is in better condition?

Cheers
Chris

[[1ponders] (Paul)]

Here ya go Geoffrey. This should get you going sweet as a button. Something for you to do on those rainy Melbourne Winter weekends.
http://www.astronomyboy.com/cg5/

But if you want to get straight to the chase:
http://www.astronomyboy.com/cg5/dec3.shtml

[Starkler (Geoff)]

Paul thanks but I've been there already.

Chris, its not a worm mesh issue or even end to end axial slop of the worm in its housing.

Imagine if you will that the shaft of the worm gear runs through a hole at either end of its housing. Its as if the hole in that housing is too big and the worm can move at right angles to its intended axis of rotation.

I'm hoping that someone has struck this.

[mick pinner]

sounds like the hole in the housing needs to be bushed and the worm realigned.

[casstony]

If the holes in the worm housing are too big, can you compensate by moving the worm a little closer to the ring gear? When I worked on my mount I found the worm gear adjustments to be extremely fiddly - you think it's right, but in actual use it's not, so you adjust it again.

[Starkler (Geoff)]

I have just come inside from the shed and Mick was fairly close to the mark.

The worm shaft runs inside brass bushes at each end. These bushes are slightly smaller than the hole in the housing that they fit into to and the space is padded out with O rings. This horrid arrangement allows the worm shaft to move sideways under tension, compressing the side of the O ring

The fix would be to make new bushes either from brass, or replace the O rings with hard nylon or similar material rings, both of which are beyond me considering that I dont have a lathe

This site here explains it. and the pictures tell the story.

[danielsun]

Geoff, I had the same problem and just the other week finished overhauling my EQ5. I was having all sorts of problems including major backlash and each night they were getting worse and at one stage the Dec began to lock at a certain point until i pulled it all down realigned and re tightened everything.
I had to tighten and re-adjust all the mounting plates which hold all the motors and gearing and whilst in the process square up all gears. (I found that all the mounting plate bolts RA and DEC had come loose) Make sure your gears grub screws and the silver knobs that hold the gears are tight .
Also when squaring up your gears don't have them meshing hard into each other, Allow a small fraction of a gap .
I just went right through every single bit and am very happy with the way its running now.
I hope this helps.
I am shortly going to put it up for sale after just buying the HEQ5 pro.

[danielsun]

In amongst all that from the last post it is the worm gears and the motor gears that had to be adjusted, realigned and tightened.