Ok, what are the 2 screws for?

[Marko of Oz (Mark)]

On my on the bottom of my Crayford type focuser.

cheers

[iceman (Mike)]

Most likely to adjust the tension of the crayford. Sometimes if they're too loose, the crayford can have a tendancy to slip - especially with heavy eyepieces.

[matt]

Yes.

One is a tension adjustment screw, the other is a tension locking screw, for when you're happy with the tension adjustment.

[Starkler (Geoff)]

Top one is a tension adjustment.
Bottom one is a focus lock. If any tension at all on this you may loose half of your focus travel, so leave it loose or better yet take it out completely so you dont loose the screw.

[acropolite (Phil)]

Geoff is right about loosing the lock screw, I am going to put a spring under mine to provide a bit of tension so it can't work loose.

[GeoffW1 (Geoff)]

Originally Posted by Starkler

Top one is a tension adjustment.
Bottom one is a focus lock. If any tension at all on this you may loose half of your focus travel, so leave it loose or better yet take it out completely so you dont loose the screw.

Also be wary of doing up this focus lock screw too tight. In my early attempts at learning my way around a Crayford focuser, I did so, and jammed the screw in there. It would not back out no matter what I tried.

I then discovered it was aluminium (!) when the knurled head twisted right off ! Did I ever feel a fool. Not really the way to learn your telescope, by destroying it !!

So I used the other screw to identify the thread series and bought a machine tap. I drilled the jammed screw to the minor diameter almost full length, and then picked out enough of the thread to start the tap. It helped that nothing around there is hardened. That went quite well.

Then the original twisted off screw head got drilled and tapped too, and a longer screw of the same thread put through that with a drop of Loctite.

It was a very cosmetic solution, but I felt like I was trying to recover my original bit of hamhandedness.

GeoffW1