Customizable Helical Crayford Focuser for Newtownian Telescope

thingiverse

This is a helical Crayford Focuser designed for amateur Newtonian telescopes. It accommodates 1¼″ eyepieces and can be easily customized to accept 2" eyepieces. The ball bearings' mounting angle is set at 5°, allowing each full rotation of the draw tube (outer diameter D=35mm) to move inward or outward by a precise 9.6mm due to the trigonometric calculation tan(5°)πD. This results in very fine focus adjustments. The design comprises two parts: the actual focuser and an adapter to attach the focuser to the telescope's cylindrical tube. The shape of the latter depends on the telescope model or may not be necessary at all for certain telescopes. In addition to the 3D printed components, several items are required to complete the focuser: * 7 machine screws M3x25mm * 1 screw M3x16mm, preferably made of stainless steel * 3 screws M3 with variable length for mounting the adapter to the telescope * M3 nuts and washers * 6 (stainless) steel ball bearings type 623 The draw tube should have an inner diameter of 1 1/4" or 32mm and an outer diameter between 34mm and 35mm. Its length depends on the position of the intermediate image in the telescope relative to the focuser's position, as well as the eyepieces used with the focuser. In most cases, it should be shorter than my version, which is relatively long (125mm, with 60mm usable travel). For suitable materials, I experimented with aluminum and stainless steel, but plastic may also be a viable option. However, commercially available steel or aluminum tubes often lack sufficient roundness for smooth focuser operation. To address this issue, I had the outer diameter of the tube reduced slightly using a lathe in a nearby metal workshop. The design relies on the following OpenSCAD libraries: https://github.com/openscad/MCAD https://github.com/JohK/nutsnbolts Update: The customizer now displays more meaningful parameters. Print Settings: * Printer: SLS * Resolution: 0.1mm * Notes: The focuser was printed by http://www.rapidobject.com using their cheapest SLS material (PA 2200).