Any lathe motor / clutch experts in here?

Evening all, nice out, isn't it?
I'm hoping to pick some brains, I recently acquired an ancient and abused [1] Challenger lathe[2], mainly for the tooling and motor that came with it,
and I think I'd like to get it running to get back in the hang of machining while I find what I'm actually looking for (a Holbrook would be nice...) at a price I can afford!
Being a fan of skips, the dump etc. I came across an old Audi air-con pump complete with electromagnetic clutch for two quid[3], dismantled it and found it's pretty simple to adapt (apart from the spline in the hub, would have to bore it and cut a keyway) - I believe that these are called on to transmit upwards of 5HP (certainly putting 12V at 4A up it locked it pretty firmly), it occured to me that I could use this as a drive clutch for the 3HP (eek! possibly a bit over-sized for a small lathe...) single-phase motor that came with the lathe, on either the motor output shaft or the countershaft-that-needs-to-be-built, can anyone see any glaringly obvious snags that I haven't?
I've had the motor connection box open, and have sussed out how to reverse it, should I want to, but would like the added safety of braking it - I've seen a few references to DC braking, wonder if anyone has had any practical experience of it? I assume that it's just a case of dumping Several Amps into the motor coil and letting back-emf/induced current in the rotor drag it to a halt?
Thanks in advance for any help!
Dave H.
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(The engineer formerly known as Homeless)

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Dave H. wrote:

You want to use if for a drive clutch, or a motor brake? If a drive clutch, that coil may require up to 30 amps of 12V. Not sure what you would gain by adding a clutch
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That coil is no more than 5A max at 12V. But the peak pull current is higher round 15A.
--
Uffe Brentsen



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"RBnDFW" wrote...

Well, I was looking at using it as a drive clutch - having only single-phase 230V I'm limited to a single-phase motor, and they don't much like being started and stopped too often, tends to shorten the life of the centrifugal switch and windings due to the increased start current (the run cap's 25uF versus the 150-200 uF for the start cap, likely to be 6 to 8 times the current on start-up) - hence the intention to run it continuously and use a clutch in the drive to the spindle.
With 12V on the coil as per use in the car it came from, it locked up pretty solid, couldn't shift it with a self-grip wrench, and it was drawing about 4A from a DC supply - I'd guess that in its intended application it'd be running at upwards of 2000 RPM and transferring perhaps 4 or 5 HP, that's about the power loss for aircon in most medium-sized cars - my rule of thumb was the RPM x torque = HP, so if the RPM's halved so's the power, might transfer 2 to 3 HP?
Re motor braking, I'm aware of quite a few lathes that use DC injection (mostly at the high end?), and some 3-phase inverters have the feature, stopping the chuck in less than a ritation - seems a sensible safety measure?
Dave H.
--
(The engineer formerly known as Homeless)

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