My son wanted to build a telescope out of a mailing tube we had, so we bought a 70mm lens (300mm FL). The part of telescope making that I like the least is focuser-making. But I think I now have a Crayford-style design that is very easy to make. It is easier to make than my previous wooden Crayford and helical Crayford, and has about the complexity of my push-pull Crayford but works an order of magnitude better.
1/16" PTFE, bent into a C-shape, with the back of the C facing the adjustment screws.
mousetape.com for about $3 shipped. I stuck a strip along one side of the focusing tube.
I then enlarged the 1.5" hole in the middle slightly. My method of doing this was to use a sanding drum mandrel in my drill press with a somewhat oversized sanding drum (which would stick out on both sides past the work piece), with the work piece resting on another piece of wood with a hole in it, which was on the drill press table. As a result, I could keep the work piece aligned at right angles to the sanding drum while moving it about so as to enlarge the hole. I enlarged the hole until it was about 1.56" in diameter. I then finished the exposed raw wood with Titebond II diluted with water and sanded. I stuck another strip of PTFE tape (G) inside the focuser hole, opposite where the focusing rod will go. Then I put it all together, and it worked just fine.
Thanks: I am grateful to John Wall for the idea of putting PTFE on the focuser tube.
Update 2: I just had a bit of trouble with the wooden thread for one of the adjustment screws getting stripped. Treating the hole with CA glue helped, though.
And I added a screw on one end of the focuser tube as a stop, and I added a screw to hold the eyepiece. Because the focuser tube is only 2" long, so as not to compromise the length of movement, we drilled little depressions in the main block for the screws.