The Wire drive unit is of proven design utilising intermeshed steel wormshaft and bronze wormwheels.
It's a bit of a pain though that the wormwheel of the thread chaser dial has to be changed when doing the different pitches.
If you need a gear system whereby the speed is reduced by a considerable amount - a worm and wormwheel are worth considering.
For example, the wormwheel may be formed from sintered iron whilst the worm is made of carbon steel.
Here I drive it with the wormwheels on two side-by-side motors (red and blue).
Thus, we are left with two sawn-off chassis blocks with wormwheel, axles, motion, cylinders and front coupler.
The 120-tooth wormwheel drives the first gear of the bevel gear cluster via the shaft to which both are affixed.
In a worm gear set the contact between the teeth of the worm and of the wormwheel has a high degree of sliding compared with other types of gear.
The worm always drives the wormwheel and never the other way round.
It is important to note that all of the multi-start worms will carry precisely this angle, and it is this that allows them to use the same multi-start wormwheels.