Hi. An acquaintance has presented me with a thing labelled "Clarke Motor". This is a 1475 rpm motor coupled to a "headstock spindle" via four-step pulleys on the motor and driven shafts. The whole thing is enclosed in a pressed steel A-shaped enclosure. He wants to get the driven shaft down from its present minimum of 850rpm to around 180. So abount 8:1 reduction from the motor speed. My question is this: given that the maximum (rim, not PCD) diameter pulley that can be accommodated on the output shaft without modifying the enclosure is 100mm, can this be done in one stage, and if so what belt profile would be best? There is almost no torque requirement I guess – he just wants to run an embossing wheel (think single wheel knurler) round leather-hard clay mounted on the output shaft. I think there would be room in the enclosure for a countershaft if necessary, but I'd rather keep it simple if pos.

Regards, Bob

Thanks for all the suggestions / comments. I had read somewhere that there was a minimum diameter for pulleys, but didn't hunt for 'official' data because I thought they would probably apply to situations where torque transfer is an issue, which it really isn't in this case – hence asking here for more 'what you can get away' figures. Inspired by Neil's remembering of his Hoover belt fitting youth (I'd forgotten about those things) I've had a look at a defunct Dyson which I got off Freegle 'for parts'. The cleaning brush is driven by a half-inch flat rubber belt direct from the motor shaft and is the right sort of length (it's quite stretchy), so I'm going to give that approach a go because it's cheap and simple to do. If it doesn't work, not much lost, and I' ll do it properly with a countershaft. A subsidiary question though – am I right in thinking that for a flat belt transmission the crown should be on one wheel only? I imagine that if both are crowned, and they aren't perfectly aligned, they will fight for control.

Jason, if it would work, the dimmer switch idea would be ideal, but as this an induction motor (I should have said that ) I think it won't.

Bazyle, the friction drive idea had occurred to me but because the input/output shaft distance is 130mm (should have said that too!) it doesn't add up within the space constraints. Thanks anyway – it would have been a neat solution.

Regards, Rob.