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What @bR39Da said, combined in some cases with duel speed motors as well!
Unsure about the 140 but the older L5 had a 0.96 ratio on them (ie 500rpm in would give 480rpm at the spindle, 781.25 would give 750, 1302 would give 1250 etc) and the speed plate would be changed depending on which motor/pulley combo was fitted. If its the same as the L5 then the input pulley is ~140mm and you can work things out from there (or at least as close as makes no significant difference).
Unsure about the 140 but the older L5 had a 0.96 ratio on them (ie 500rpm in would give 480rpm at the spindle, 781.25 would give 750, 1302 would give 1250 etc) and the speed plate would be changed depending on which motor/pulley combo was fitted. If its the same as the L5 then the input pulley is ~140mm and you can work things out from there (or at least as close as makes no significant difference).
....Also 1.1Kw/1.5HP is a bit weedy. I know it's original but personally I'd be going for a 2.2Kw/3HP along with aligning the speed with what you were using it for rather than the original speed! eg if using it for small stuff/aluminium with carbide/insert tooling wind it up to 2000rpm (as that was an option) using a 2 pole motor with and somewhere around a 2:3 pulley ratio.
I agree, particularly with a mere 1.1Kw motor.
I've done it with mine...but I've got a modern Weg inverter rated 2.2Kw motor on it! Even then, I bumped the pulley size up because I'd rather underspeed the motor than overspeed it (the motor is the noisiest thing so particularly if turning late at night I like to keep it down around 33Hz or so).
On the assumption that it has the same ratios as the older L5 and a 140mm driven pulley then I'm going with somewhere between a 76mm/3" and 78mm pulley. Certainly that should put you in the correct ballpark. I'm reasonably sure the gearing is the same as the L5 but not 100%, should be easy to verify, in top gear, one full turn of the input should be 345.6° of the spindle (or if you can't measure that then 25 turns of the input pulley should be 24 turns of the spindle).
Generally the slower the speed the lower the motor rating. Schools, training etc had smaller motors and while I've no idea of the speeds/HP for the 140 there is some info on the L5
31 to 720 rpm - 1.5 hp 1500 rpm motor
42 to 960 rpm - 2 hp 1500 rpm motor
62 to 1440 rpm - alternative range with the 2 hp 1500 rpm motor
31 to 1400 rpm - 16 speeds: two-speed 1.5/3 hp 1500/3000 rpm motor
62 to 1400 rpm - 16 speeds: alternative range with two-speed 1.5/3 hp 1500/3000 rpm motor
22 to 500 rpm - 1 hp motor
34 to 750 rpm - 1.5 hp motor
45 to 1000 rpm - 16 speeds: 2-speed 1.5/3 hp 1500/3000 rpm motor[1]
34 to 1500 rpm - 16 speeds: alternative range with 2-speed 1.5/3 hp 1.5/3 hp 1500/3000 rpm motor
So in general 500rpm - 1HP, ~750rpm - 1.5HP, ~1000rpm - 2HP, ~1500rpm - 3HP.
When I came to replace mine I went with the spec of the largest original motor (ie 2.2Kw/3HP) on the basis that with a VFD it was trivial to change the speeds.
I'm reasonably sure the 140 would be perfectly fine for 2000rpm with a suitable motor and that's where I'd be aiming for personally.
[1] I'm sure this is wrong. I suspect it's actually 45 to 2000rpm (or 22 to 1000rpm).
Yes. More just to verify my assumption on the gearing was correct!
