1.25" Crayford Focuser for telescopes v2

A while I ago I made the https://www.printables.com/model/125438-125-crayford-focuser-for-telescopes model and it has been popular. But I wasn't that happy with the 3D model, way too many little things patched up or added in a later sketch when it could have been a lot simpler. Also I wanted to add a geared drive, and a stepper motor for hands-off focusing.

Mounting holes are still 57mm square. I still don't have any guide as to what the most common mounting pattern is but this seems to work for most, and if it doesn't you can print a simple adapter. Keep it thin, it will probably retain the focus range you need.

If you're happy with the first version and have no interest in a motorized focuser you may be interested in the new drawtube, the rest is not all that different. The drawtube now has a version with a screw collar. If you were using a metal bolt on the old version to fasten eyepieces that may have scratched the eyepiece. A nylon bolt was OK though would not last forever. This new version uses a screw collar to compress a printed split ring that will grab onto the eyepiece more securely and without any risk of scratching. It grabs my Baader Mark IV Zoom really well, Astromania 7-21 Zoom less well - YMMV. You could try printing the compressing ring with flex filament.

This model has some basic improvements. The barrel surrounding the drawtube is slightly thicker. There are no more heat-set brass inserts mounting the front cap, they were too hard to insert in that position - now nylock nuts are inserted, pull them through with a long (~30mm) bolt from the front. The bolts holding the four bearings have their heads facing the other way so they are more accessible. To make clearing supports easier the holes for the four bearing bolts now go right through. Both bolt head and nut recesses were placed in a way that could break through to the inside of the tube, they now don't. The nuts can be pushed sideways out of the slots if you want to disassemble. The four bearings are moved inwards very slightly for better drawtube engagement and move in a wider cut for smoother operation. The pinion block moves more freely in a slightly taller cut at the front.

If you want a gear reduction there is provision on the side of the body to mount a 4:1 belt drive reduction using GT2 gearing. This is done using a 20T pulley and an 80T pulley with 200mm belt. The printed part for the 20T assembly requires a 40mm shaft, two 5mm ID 10mm OD 4mmW (105-ZZ) bearings. When in place slide it back to tighten the belt just enough so it does not skip and tighten the two 25mm bolts. 

If you want to mount a common NEMA17 stepper motor instead, print the stepper mount and attach that with 12mm bolts. The stepper has the 20T pulley attached to its shaft and connects to the 80T pulley through a 250mm belt. You can control the stepper with any of the free focuser software out there. 

I'm playing with some code to control focus with a Nintendo Wii Nunchuck controller. It's not ready yet but when it is I'll upload it here. This will allow manual focus without bumping the scope, I'm thinking of using the other controls available on the Nunchuck to aim the telescope using another pair of steppers.

If not using the stepper mount or the reducing assembly then leave it off; just like the first version, put a knob on both sides.

Use M3 hardware throughout. For the four bearings use four sets of 25mm bolt, nylock nut and 3mm ID 8mm OD 3mm width bearing. At the front insert four nylock nuts and fasten the front cap with 20mm bolts. The front cap needs one flat M3 hex nut inserted to engage the tension screw.  For the tension screw I used a thumbscrew sold as replacement for a Boss guitar pedal but any bolt will do, it will just be less convenient to turn with fingers. My tension springs are 6.2mm high and 4.7mm diameter; I don't have an exact source for these but you probably could use ballpoint pen springs, though they would be a pain to get inserted straight because of their length and need to compress them while assembling. You may not need the base shim part at all but it raises the assembly slightly if needed.

I cut bearing surfaces from 10x3mm bar aluminium, three 64mm lengths. Another piece 38mm long compresses the tension springs agains the pinion block. (If you can accurately cut flat pieces of steel that would be better. I have heard carbon fibre is not good.)

Clear skies!