EQ3-2 Backlash Adjustment

[Meerkat]

Hi Guys,

Just bought a Helios 120mm F1000 with an EQ3-2 mount off of a friend and I've noticed that although the RA is OK the DEC has got quite a bit of backlash.

Having not had one before, and with no instructions, does anybody know how to adjust the backlash?

Thanks,

Steve

[RichieP]

Hi Steve

You can adjust how closely the worm gear meshes as follows:

Locate the Dec worm gear adjustment bolts on the DEC axis as per the following picture

(click to enlarge)

To engage the gears more closely, loosen the small allen bolt in the centre slightly and tighten the two larger bolts either side of it. As you tighten these, backlash will be reduced, albeit at a cost of the axis becoming stiffer to move.

I am afraid you will have to put up with some DEC backlash in this mount, I have tightened it as far as I can, and the backlash isn't noticeable using a slow motion control, but when using the Dual drives for this mount, it can take longer than 40 seconds at 8X sidereal for the slack to be taken up, so I don't bother with the DEC motor.

I am planning to strip this mount down, remove the gloop they use as grease and replace it with some high quality lithium grease. I am hoping this will allow me to tighten the gears more and reduce the backlash to a more acceptable level so I can use the motor again.

Regards

Richard

[Meerkat]

Excellent, thanks.

So I suppose a SynScan would not be worth it with this mount?

Steve

[MartinB]

If it is anything like the Vixen GP mounts (which have the same method of adjustment) it is a very delicate operation - too loose and everything slops around, too tight and the gears bind. They normally start to bind when the mount starts to slow at the end of a slew.

Some tips (from someone who has spend many hours perfecting this adjustment) - Tighten the central set screw then fully loosen both outer screws. then start to tighten the outer screws making sure they are both tightened evenly. Keep turning the drive shaft one way then another to judge how much back lash you have. Once you are getting close, with a reduced amount of backlash present you have to make tiny adjustements until you just have a small amount of backlash left. Don't try to eliminate it all together, the gears will just bind. You can reduce backlash the most if you keep the adjustment of the 2 outer screws even.

Having tuned the mount here is a good way of getting rid of residual backlash in Dec - offset the balance of the scope in dec so that the weight of the scope always takes up the backlash. This works very well.

[Meerkat]

Just completed the adjustment and it's a lot, lot better.

Thanks guys,

Steve

[Vega]

Oooh, I'll try this one next time im playing

Cheers

Matt