Minimal 1-1/4" Helical Crayford Telescope Focuser

A 1-1/4" minimalistic telescope focuser. The design is a helical Crayford where rotating the eyepiece moves the eypiece in and out to achive focus. It works rather nicely, giving a smooth and precise adjustment to focus.

This is a very minimal design, originally designed for a small RFT ball scope where absolute minimal weight and size were desired. As such there is no draw tube, rather the barrel of the eyepiece is used as the drawtube. This does lead to a few limitations...

• This design only works with eyepieces having smooth 1.25" barrel. There must be no relief cuts or safety cuts on the barrel.
• Limited travel of about 10mm
• The design is sensitive to dimensional differences. Adjust the shrinkage factor parameter to allow for material differences. ABS is the default with a 1.5% shrinkage allowance.

The stl files are rendered with the default ABS shrinkage factor of 1.5%. This could be scaled in the slicer or use the provided OpenSCAD file to allow design adjustments. The OpenSCAD customizer is supported.

Needed parts...

• 1x 3D printed ring
• 2x 3D printed bushings
• 2x 10 x 5 x 4mm MR105 ball bearings
• 2x #6-32 heat-set threaded inserts
• 1x #10-32 heat-set threaded insert
• 2x #6-32 x 1/2" socket head cap screw, stainless
• 4x #6 washers, stainless
• 1x #10-32 x 1" lock knob, nylon
• 3x #6-32 x 1" socket head cap screw, stainless, for mounting

• ABS plastic is the default, shrink factor parameter will need to be adjusted for other materials
• 0.4mm nozzle or smaller
• Heavy walls, 2mm or five line count minimum
• At least 40% infill
• Standard support on