Stiff Dec Axis on G11

[[1ponders]]

Background info:-
I recently pulled down my G11 and did a regrease on it. Afterward it was silky smooth. Nice and easy to rotate the worm by finger without binding. But I didn't seem to be able to tighten my clutches enough to lock the axis from moving easily, so I pulled the Dec and RA axis apart again to check for grease that may have wicked up onto the nylon clutch. It was dry and the problem was I just wasn't tightening it enough ( I'm used to push to with the AN so never tighten the clutches up very far.).

Anyway after putting it back together I found I had a horrendous backlash problem in Dec. I had made no adjustments to the worm/gear mesh at all. I thought the axis mightn't have been seated correctly, so I pulled it apart and put it back together again. This time I adjusted the worm/gear mesh tightly in an attempt to get rid of the BL. It still didn't seem to make any difference.

Then I looked at a star with a webcam. When I moved in Dec at guide speed the star would immediately start to move and then appear to stop and would start up again some time later. When I looked at a graph of the movement, the star didn't stop completely but slowed down and then about 30sec or more later, sped back up to normal guide speed.

That was when a Dec Motor Lags message started coming up. I know that meant that the Dec Worm is likely too tight. So I checked and it was very tight. I released both worm blocks but the axis was still stiff to move. That was with both blocks completely loosened. It would move freely without stiction, but was stiff to turn the worm. I was using one of the oldham couplers fixed to an allen key to assist with the turning and it was still firm.

Why would the axis still be stiff even after loosening off the worm. The balance is good. Could it be that when I did the regrease initially, i didn't put enough fresh grease back into the bearing?

Oh and when I remove the worm completely is spins freely in the bearings.

The only other thing i can think of is the during the second pull apart, the mount head rolled over while I was removing the Dec axis and the motor received a very small knock. I wouldn't have thought it would have affected the mount such a small knock though.

Any ideas would be appreciated

[multiweb]

The meshing is one thing. If the mesh is too tight into the gear it's hard to turn and the motor will labor, but equally, even with the lose meshing it will be hard to turn the worm if the end blocks are not perfectly aligned, so the end bearings are kinked and it's enough to stop the worm from rotating. Those end blocks have to be spot on.

[[1ponders]]

Thanks Marc, I have checked that. I use the worm cover as a guide to get them square. I guess what i was saying is that no matter if the worm and bearing blocks are firm, loose or completely undone the axis is still very firm to turn.

[Omaroo]

I think that it may have something to do with the shaft encoder installation Paul. I can't tighten mine like I used to either - in both axes - after I installed my encoder bearings and new spacers. I do (just) have enough tension so as not to slip when everything is balanced properly. I also took mine apart and tried a bunch of things to determine where they problem lay.

[[1ponders]]

I don't have the encoders on there anymore Chris. They are on the G8 along with the AN now. I've got a Gemini on the G11 now. So that's not the prob.


Tomorrow I'm going to drop the axis out again and try a bit more supa-lube on the bearings and see if that makes a difference.

[Omaroo]

Interesting...then I'd like to know what my problem is. Not that it's really a problem mind you. I'm happy not tightening anything to straining point. It has enough grip to track accurately still...

[[1ponders]]

Have you checked to see if you have any grease residue on the nylon clutch pad? It was almost impossible to tighten my G8 up until I did the clean down and regrease. It made a big difference.

[multiweb]

Sorry I misunderstood. If the axis is stiff it's likely to be water contamination in the needle bearings. It happened to me once. Over time, cold temperature, dew, etc... makes the grease in the bearing very very sticky. I used some thick lube for the needle bearing in the past. Now I only use the spray on type and put a very thin film. Might be worth taking the axis apart, turp it up and regrease it again. While you're at it get some very fine sanding paper and smooth the area where the bearing roll as it marks the area a bit too. See how you go. HTH.

[Omaroo]

Oh yes, clean as a whistle Paul. I'm very particular about excess grease. I'll remove the encoders one day and see if it's the six little stanchions that span either side of the encoder drive gear and take the compression that might be the cause. It's got to be somewhere in there.

Anyway - this thread is for your problem - not mine. :)

[[1ponders]]

I guess its always possible Marc, but I don't think that scenario is likely. It has only been a month or two since i degreased the mount (turps) and regreased it (supa-lube, very thin smears) and the mount hasn't been used more than 3 times in that period. It has been undercover the whole time.

I'll pull it down again tonight. Check the movement of the shaft bearings and all the areas that have lubricant contacting them.

[[1ponders]]

I removed the Dec axis yesterday and applied an extra smear (toothpaste thickness and 6mm long) of supa-lube to both bearings in the block. Result: the axis is even more difficult to turn no matter the worm adjustment.

Options: I have too much grease, or I'm using the wrong type of grease. Or I have grease where I shouldn't from my original clean and its sticking things up.

Thoughts?

[multiweb]

When you say bearings in the block, the small radial bearings in the worm block [they're both shielded so I don't see how] or the needle bearings inside the DEC axis? Regardless I think the bearings should only have a very thin film of spray-on or WD40. No sticky-goohey stuff. Keep the thick grease for the worm itself in the meshing area.

[[1ponders]]

I'm reading something here and I'm having a :doh: moment. Do I have my bearing surfaces around the right way.

I have: Clutch Knob, annular leaf washer, large thrust washer, thin flat washer, roller bearing, thin flat washer.

Should it be:Clutch Knob, large thrust washer, annular leaf washer, thin flat washer, roller bearing, thin flat washer?


:prey:

:doh:

[[1ponders]]

Yes the pressed roller bearings. Using my finger I applied a smear across the surface of the rollers and worked it in by running my finger back and forward around the roller surface.

I am tempted to pull it down and clean it again. But I'll wait til I see what my previous observation brings about

[JohnG]

Paul

Here is the washer order for you....

http://www.wilmslowastro.com/tips/g11gemini.htm#washer_assembly

You really only need a slight smear of Lithium grease on the bearings.

Cheers

[[1ponders]]

Thanks for the link John. After 3 or 4 years (however long I've had the G11) I'd never come across that page before until last night. And then you post the link. I'll take that as an omen :lol:

I think I'll be pulling it down tonight, cleaning out and regreasing again, just to make sure.