Spindle gear wheel for 1970s 'Royal' yarn winder

This is a replacement spindle gear wheel for a 1970s 'Royal' yarn winder.  It may be common to other brands from that era.

My sister discovered that they don't bounce very well, but despite everything being rather old and brittle this was the only part that broke.

I split the gear wheel into two parts to make printing easier.  One is the main gear wheel itself. The other is a boss key that glues into the hole in the centre of the gear wheel and onto the spindle.  I have also uploaded the source OpenSCAD file in case you wish to modify the design.

Design:

The gear ring is built up from 60 individual gear teeth blocks, each one of which is produced by extruding the end profile, and applying an extrusion scale so that the teeth taper.

To produce gear teeth with rounded edges it uses Kurt Hutten's excellent 'round anything' OpenSCAD library.

Despite carefully measuring and calculating everything, some trial and error was involved in shaping and scaling the individual blocks so that they fit closely at the correct diameter.

Printing:

I printed this on a Prusa MK3S+, in ABS, using the default '0.10mm DETAIL' profile, modified with 100% infill and External perimeters first.  I had a bit of stringing between the gear teeth on the last few layers, which I cleaned up with a heat gun.  The gear wheel prints without supports.  I also printed the boss key without supports, but you may prefer to add supports to the inside of the keyway to guarantee a clean print.

Assembly:

The original gear wheel is bonded to the winding handle spindle, over a ‘key’ part that fits into a keyway.  The remains of the old gear wheel and glue will need to be removed, but taking care not to damage the key part.  I used pliers to crush the remains of the old gear and glue off the spindle, without realising there was a separate 'key' piece underneath - hence the signs of damage in the last photo (which shows an earlier iteration of the gear wheel, made before I learned about this 'key' part) - but I was left with enough of the key to fit into the boss STL. 

Remove the circlip on the end of the shaft, withdraw the shaft, slide the boss key and the replacement gear onto the shaft and reassemble with the circlip.  Slide the boss key and gear wheel along the shaft until the gear wheel meshes with the small cone gear, then glue both parts in place using plenty of epoxy glue.