I first saw a helical Crawford type focuser at last year's gadget night (a annual idea exchange at VAS), when Bob brought one in. The tension bolt or set screw doesn’t have a spring, I put a threaded insert into the side of the piece of maple. The key aspect of construction was bearing angle, one of the bolts is straight which guides the focuser tube and the other is tilted at a 5-10 degree angle so the focuser will rotate in
