Non-rotating helical focuser with collet for Hadley telescopes

The Hadley telescope by Maff is a great design that allows makers for an easy and cheap introduction to astronomy.

There are lots of difficulties when using a telescope for the first time, for me one of them was trying to take a picture with my phone attached to the eyepiece through a mount. With the original focuser the eyepiece rotates when you adjust the focus, so it was necessary to adjust the quite often. Also, if the phone is not perfectly balanced in the eyepiece its weight can make it rotate.

This design tries to avoid this problem so it will be useful when using a phone/mount or an astro-camera.

The focuser is composed by several pieces:

1. Focuser base: has three slots that impede the rotation of the main tube
2. Focuser tube: it has a M56x5.5 thread (not that it matters) and it's 72mm long, providing the same total travel as the original focuser by Maff. It fits into the base, sliding without rotating. Update 26/10/2022: there are now three versions of the focuser tube, the original one which has 0.5mm of tolerance per side of the thread and two new ones, with 0.25mm and 0.37 of tolerance. For my particular 3d printer (custom made) the best one is with 0.37mm of tolerance. I recommend printing just 1cm or so if you want to test the fit before doing the full piece.
3. Focusing nut with retention ring: this nut has to be printed in two pieces, the retention ring fits along the focuser bearing surface and then it has to be glued to the focusing nut
4. Collet: the collet eliminates the need to tighten three different screws that could mark the surface of the eyepiece. The collet should keep the eyepiece perfectly centered. Three small pieces of electrical tape should be placed in the inside of the collet to improve the grab of the eyepiece, with this, the eyepiece is well secured in place.
5. Collet nut: the collet nut will force the collet downwards which will in turn compress it so it grabs to the eyepiece

Apart from the usual cleaning of the pieces, it is recommended to do a dry fit before gluing with CA glue the retention ring. Don't use too much glue! The nut should be able to rotate with respect to the base.

After gluing make sure that the nut is rotating freely, if there is too much force try to put a bit of oil.

Printing:

I printed my parts with these settings:

Nozzle: 0.4mm

Layer height: 0.2mm

Infill: 30%

Supports: none

But any settings you used for the rest of your Hadley telescope should work with these

I made a small video showing the gluing and assembly process:

Focuser installed in the telescope:

I have included the original design files, I used FreeCAD 0.20, feel free to modify the design to your needs!