ATM: Crayford focuser

[Andres.Dandler.97@Alum.Dartmouth.ORG (Andres Dandler 97)]

Hello!

I've made myself a Crayford-style focuser, with 4 ball 
bearings from a hobby shop.  Right now it's a prototype 
version, to see whether my concept works, and it does. As 
the drawtube, I'm using the Aluminum tube of an old T-mount 
that I never use.  It has a nice and smooth outer surface, 
machined.  I'm not planning on machining a flat (should I?  
Is Aluminum ok?).

The problem:  I've noticed that the drawtube slips when I 
press against it (axially).  So if I had a really heavy 
eyepiece, it would slip in (or out) of focus.

How do you whizzes out there solve this?  A thumbscrew knob 
to lock the drawtube in place once I've achieved focus?  Or 
maybe a teflon rubbing surface somewhere to add some 
friction?

Oh, another related question:  I'm just now figuring out how 
to mount the focus shaft (3/16" steel) in place.  I have 2 
more of those little ball bearings.  Should I use them?  Or 
do I want something that actually gives me some friction?  I 
wonder: if I have ball-bearings everywhere, isn't the 
drawtube just going to slide in and out on a whim?

Any advice is appreciated.

Thx.

   -Andres