Harrison M250 Change Gear Calculator

This tool can calculate possibly alternative gears that can be used to cut a particular thread on a Harrison M250. It works with either a 6 mm pitch leadscrew (the default) or a 4 TPI one (although I've done limited testing of the imperial version). It is heavily based on the work of Al Harral; I just thought it would be nice to have a web-based alternative for those (like me) who don't use Windows very much.

The code is based on Al Harral's GEARS.BAS so I certainly can't claim any credit for the intelligence behind this code: I simply ported it to javascript with some modifications to cope with the gearbox on the M250 and added some logic to make sure the gear combinations are possible with the banjo.

I haven't done a lot of sanity checking on this calculator yet, so if you notice any mistakes or problems, please don't hesitate to get in touch.

Leadscrew: Metric (6 mm pitch)
Imperial (4 tpi)
Available Gears:
Just standard gears (22, 40, 44, 80 & 88)
Include extra gears (above plus 30, 35, 56, 63, 72 & 84)
Include all gears (above plus 28, 40, 60, 76, 78, 81, 84 & 92)
Target Type: Metric Pitch
Imperial TPI
Target Pitch:
Target TPI: