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EQ3-2 DEC drive backlash


JamesF
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[This is for the older EQ3-2 mount with external "aftermarket" motor drives fitted.]

It's not a major problem and I can live with it if I must, but it is *quite* handy to be able to tweak the DEC axis once in a while if I start imaging and then discover my polar alignment is off.

Are there any handy hints for improving the behaviour of the DEC gearing on the EQ3-2? I think some of the problem is down to the internal drive itself as motion isn't that smooth even using the manual control, but with the motor drive it's far worse.

James

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Dec wobble is a bit annoying on the EQ3 but you can fix it. Here's a poor image of the dec worm gear housing below the dovetail...

IMAG0261-1.jpg

What you need to do is use an allen key to loosen the middle grub screw and the tighten the two tightening bolts as well as the ones under the chin. You'll find the backlash goes but the slow motion control is very tight so tightening the grub screw eases this. You need to fiddle with the balance of the grub and the two bolts on either aide but you'll get it right eventually.

If you're doing this you might as well re grease the whole thing while you're at it.

Hope that helps.

Edited by Parus major
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That's really helpful. Thank you.

Would I be expecting rather too much if I asked whether there was any kind of maintenance manual for these mounts? I would be, wouldn't I? :)

James

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Yeah, it would be handy. If you want to strip out the whole dec assembly it's fairly easy. You just get a spanner the right size and open the polar scope objective cover, affix to the nut and turn the dec until it comes off, remove the worm gear assembly using the four bolts mention above. Regrease after a good clean and put it back together. I'm a mechanical simpleton and I managed it much to my surprise.

It's performance is like night and day after this, well worth the hour or so it takes.

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  • 5 years later...

I had a fair amount of slop in me EQ3 Pro DEC axis.  I ended up removing the whole worm drive unit and noticed the spindle that runs through the length of the drive had a bit of sideways play/movement.  On the outside of the drive, where the motor cog fits, I found a biggish lock nut which I removed and this allowed me to tighten another nut and removed the sideways play.  After reassembly and following the above procedure, I now have a much improved system.

 

Even with the nuts at their tightest (so I can hardly turn the DEC slo-mo control) I can still wobble the dec axis by about 1/2 a degree (approx!) but when I loosen the nuts to get a reasonably smooth action the wobble isn't noticeably different.

 

I'm probably getting all fussy over this now  (just spent a happy 2 hours fiddling with the DEC axis...)  I mustn't forget that it's still a world better than my old EQ2 :-}

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