Knocking & jerking used EQ6, not pleased, need to rant!

[ollypenrice]

I bought a second hand EQ6 for £250......so I saved about £700. Stripped and re-built now it's a sweet runner.

The boy done good!

Olly

[1parsec]

Hello Chris,

Dave here from Rowan Astronomy

There have been some good suggestions on what the issue may be with the knocking and I'd like to add to those if I may.

You can determine if it if an issue with the 12t or 47t pulley by removing one of the bearing end covers off and look at the end of the worm shaft.

If the clunk is every rev of the worm it's related to the worm / 47t pulley . If it's 4 clunks per rev it's the motor end / 12t pulley

1.

Check the 47t pulley has been fitted fully on to the worm shaft to give the ~1mm dimension shown in step 19. in the fitting instructions.

If the worm shaft does not protrude, the face of the pulley can rub on the inside of the worm carrier casting / bearing.

You can adjust the bearing retaining rings at both ends to position the worm so there is small gap between the pulley and the side of the casting. 

2.

Check that the grub screws in the 47t pulley are in their correct positions. They are different lengths, the longer one should

be fitted so it clamps down on to the flat on the worm shaft. The shorter screw clamps on to the plain diameter. If these have been reversed the

longer screw may be too high and touch the scallop in the worm carrier casing and clunk every revolution.

I hope you get it sorted and let me know if I can help further.

Dave.

[Gazabone]

The sellers initials weren't GD were they? Worth checking :-) that's terrible, I don't know how people have the concience? Maybe you could recoup a bit of dosh buy selling it with an honest appraisal from yourself?

No, not GD. Selling it on honestly is an option. It came with the motofocus and although I had to spend £70 or so to get the hand control for it, I could probably recoup £100 by selling that separately.

I might see if if can be professionally restored to good working condition as it seems in other ways a really nice scope, no marks, dents etc. there is a bit of mirror creep but I think that's down to the grease congealing, as it will in time if the scope isn't used, so a very minor problem.

Alternatively, might make an interesting project for me, if I end up wrecking it, it wouldn't be any great loss, just don't want to throw it out as I'm sure there's a good scope in there somewhere!

[Chris]

Hello Chris,

Dave here from Rowan Astronomy

There have been some good suggestions on what the issue may be with the knocking and I'd like to add to those if I may.

You can determine if it if an issue with the 12t or 47t pulley by removing one of the bearing end covers off and look at the end of the worm shaft.

If the clunk is every rev of the worm it's related to the worm / 47t pulley . If it's 4 clunks per rev it's the motor end / 12t pulley

1.

Check the 47t pulley has been fitted fully on to the worm shaft to give the ~1mm dimension shown in step 19. in the fitting instructions.

If the worm shaft does not protrude, the face of the pulley can rub on the inside of the worm carrier casting / bearing.

You can adjust the bearing retaining rings at both ends to position the worm so there is small gap between the pulley and the side of the casting. 

2.

Check that the grub screws in the 47t pulley are in their correct positions. They are different lengths, the longer one should

be fitted so it clamps down on to the flat on the worm shaft. The shorter screw clamps on to the plain diameter. If these have been reversed the

longer screw may be too high and touch the scallop in the worm carrier casing and clunk every revolution.

I hope you get it sorted and let me know if I can help further.

Dave.

Wow, there should be a double like button for posts like this! :-)

Thanks Dave that's a great help, I'm hoping to book some time on the mount with my wife for Sunday so I can get stuck in again :-)

[Chris]

A bit of an update I've now re-stripped the Dec axis armed with the above knowledge and corrected one or two little things. I noticed that the replacement gear for the worn shaft was catching on the cast metal of the mount as suggested above, I tried re seating the gear a bit further along but I think it only went an extra .5mm and I could only adjust the circlip at one end of the worn carrier so I decided to file a couple of mm from the casting to stop it catching.

Also when I re-installed the motor with the pulley system I secured the motor so the belt was pulled a bit tighter this time after noticing the knocking noise happened more when the mount was out of balance so wondered if the belt could be skipping teeth (I also did this with the RA pulley belt).

One interesting thing I noticed was that if I tightened the worn carrier circlip too much the worm gear became very stiff and hard to turn. I have now decided to have the circlip slightly loose on both RA ad Dec which does introduce about 0.3 degrees backlash/play in both axis but the mount now runs nicely! I did try tightening the circlip again to take up the remaining backlash and to see how it ran but this resulted in mount occasionally stopping during a slew and making a humming noise which I assume is the stepper motors stalling so I loosened the circlips off a bit and it returned to running fine again.

I think I'll have to live with a small amount of backlash bought in by having the worm carrier circlips fairly loose but on the flip side the mount does now work properly and it sound nice, no coffee grinding noise!

Now I have my 0.7 reducer for my C8 Edge I'll try and get some short unguided subs to see how well the mount tracks for imaging? I can then see if its even worth setting up guiding or not?

Thanks for the help guys  

[Chris]

I mean this "ball bearing nut". If you tighten it too much, the worm will get stuck.

You're right on the money thanders, its a shame that you need to slacken the circlip off to the point where backlash is introduced, did you find the same?