Crayford style focuser slipping issue

[Nico13]

Hi all,

In the process of setting up a Meade 8" SC and had read about and also was advised to get myself a crayford focuser.
Well as I don't have a big budget for this stuff was pleased when I was offered one at the Bintel shop for less than a $140. Now this unit has the Bintel name on it and it looks the ducks guts, nice finish and smooth operation, no slop and with a 10:1 also. :)

When I got it home and mounted it on my little scope I found the focuser drive mechanism that turned out to be a friction drive would hardly lift its own weight let alone with a barlow and eye piece added.

Now it has a tension adjustment but when this is wound up the 10:1 just slips as well so I was wondering has anyone else bought one of these and had similar problems or is this just a case of you get what you pay for. :(

Thanks for any help you can offer.

Nico.

[asimov]

It's a common problem with a lot of crayfords. The simple fix is to take the drawtube out of the focuser & get the flat part perfectly flat using an oil stone.

Forgetting about the fact that a refractor drawtube/focuser is used in this procedure, the process is the same for all.

http://andysshotglass.com/100EDdrawtube.html

[bojan]

Well designed (metal) rack-and-pinion focusers are actually better than Crayfords.. And they will never slip.

[astro744]

I have the Newt version of the same focuser and I got slippage after a year of use. Mine has two set screws and the second one closest to the tube now does nothing. I found that by increasing the tension on the first screw (closest to the eyepiece) I can get enough tension to hold the eyepiece. Once this screw fails I'll look at a better focuser.

[erick]

The screw closest to the optical tube is a lock screw. It is designed to set the draw tube at that point and it disconnects the adjustment, which just spins without effect. I have had several Bintel 1:1 and 10:1 focussers and have always been able to find a spot on the tension adjustment (the screw furtherest from the optical tube) to have the crayford mechanism work effectively, even with heavy eyepieces. Yes, you might have to adjust it as the temperature changes and as you change eyepeice weight. Maybe I have been lucky - I've never had to service one. See a few previous threads and links:- http://www.iceinspace.com.au/forum/showthread.php?t=36706 http://www.iceinspace.com.au/forum/showthread.php?t=51192

[Nico13]

Thanks guys,

Yes looks like I'll just have to have a bit of a fiddle with it and remove the draw tube and check the out the mechanisms driving surface etc.

The locking screw (Closest to the OTA) works fine but I wasn't aware it disengages the the friction drive when set, I think I had it backed off sufficently when testing but will have another look at that.

Thanks again, will have a play and see how it all goes.

Nico.