Crayford Focuser with Motor Mount for 6" Newtonian Telescope

thingiverse

This is a remix of this Crayford focuser (https://www.printables.com/model/125438-125-crayford-focuser-for-telescopes). I have heavily modified it to suit my needs and available hardware. These are also similar: https://www.thingiverse.com/thing:5167331 https://www.thingiverse.com/thing:4705423 And this motor mount is similar: https://www.thingiverse.com/thing:5597193 I wanted to try astrophotography with my 6" Celestron Newtonian, but couldn't reach focus with the stock focuser, so this one had to be lower profile. I also didn't want to cut any holes in the optical tube, so I couldn't use a standard 2" drawtube. Finally, I wanted to use an Arduino and a stepper motor to create an autofocuser. The .step and .f3d files is provided to make modifying the design much easier, and to see how the parts fit together. Also the PCB .sch file is included. I use this Arduino code (https://github.com/DeepSkyDad/AF3), which I compiled for the Pro Micro and TMC2209 I already had. The PCB is single-sided, so conceivable someone could make it at home. The toner-transfer method has never worked for me, and a prototype with wires on perf board was too bulky. It is mounted to the back of the motor with a printed base by replacing two of the motor screws with extra long M3x40mm ones. The top of the case is untested, the clips don't really work. The motor is a standard NEMA17 from a 3D printer. It is overkill, but I already had one collecting dust. If not using the motor mount, print the Pinion Block Cap instead. All motor mount screws and thumbscrews are M4x10. Bearing screws are M6x16, and had to be drilled out a bit so that the threads would bite into the plastic the right amount. Too tight, and the plastic could crack and ruin the whole thing. The screw holes on the opposite side of the motor mount are for an alternative belt-drive I was experimenting with, but ultimately abandoned. This was removed from the .f3d file included here, along with those failed attempts. The bearings are the same size as those used on the worm gear of the AVX mount, S686ZZ 6x13x5mm. The pinion shaft is a 5mm steel rod. The tension screws must be pretty tight, but even without filing the drawtube flat at this contact point as many others do, there is enough friction to hold a DSLR in place. The drawtube is an aluminum M42 extension tube I found on eBay, 110mm long. Do not print the one in the model. Once I checked that it worked I cut it down so that it doesn't interfere with the light path, thus improving star shapes considerably. Also allows screwing on an astrophotography camera directly. IMPORTANT: I also drilled and tapped holes for two small screws at the top and bottom of the drawtube so that it can't come out of the base, extremely important if using the autofocuser function unattended with expensive equipment. The slot in the drawtube cavity allows the screw head to pass, and a twist locks it in place.