I've done this project a while back, but in case anybody is interested, I am documenting it. My Coulter 8" scope came with a friction focuser made of pipe fittings that Coulter described as "helical", I think because you aren't going to do very well just pushing the focuser tube in and out unless you give it a twist as well. With practice, the focuser was usable for light eyepieces, but it really didn't work for something as heavy as a Hyperion 13mm (and there are eyepieces heavier than that). So I decided to make a helical Crayford focuser, because I was too cheap to buy a KineOptics one.
The idea behind a helical Crayford is that you have ball bearings against which the draw tube rotates. However, the ball bearings are slightly twisted so that their axes make a small angle with the angle of the tube. Consequently, as you rotate the draw tube, it moves in and out. If the ball bearing angle is larger, the movement is faster, and if it's smaller, the movement is slower.
bondable PTFE JB Weld'ed to a piece of metal, with the thumbscrew bearing against the metal, all as in my push-pull Crayford. For the draw tube, I used the aluminum draw tube from the Coulter. In the picture, the hole for the focuser tube wasn't cut yet.
Eventually, I unscrewed the posts, cut a hole of the focuser with one of my trusty cheap Harbor Freight hole saws, sanded the faux veneer off the particle board, glued the posts with JB Weld to the particle board, with screws for added strength. Or something like that--I don't remember all the details. (It's possible that at some point the posts were weakly affixed with craft glue to help with layout and then pushed off.)
The focuser has had a bit of image shift, which has increased with age. Lately, it wasn't doing too well, so I had a closer look at it. It turned out that the T-shaped supports, under pressure, had rotated further, so that the angle between the axis of the ball bearings and the draw tube was too big for good movement. I made the angle smaller, added washers under the nuts (did I forget? or maybe I just ran out of washers?), and tightened it up. I am guessing they'll rotate away again. If they do that, and maybe before that, I may replace the nuts with locknuts, and/or add some toothed washers.
The focuser weight is an issue--I've had to increase the counterweight--but that's part of the price of making stuff out of wood. And the price is hard to beat: a couple of bucks for the bearings, and then some screws, washers, nuts, square rod, and various pieces of scrap.