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.
--
(The engineer formerly known as Homeless)

"Rules are for the obedience of fools, and the guidance of wise men" -
Douglas Bader

[1] broken teeth on the bull gear (known weakness), missing backgear
shaft... may not bother fixing that can of worms
[2] 10" swing, 24" b.c, changegear screwcutting and longitudinal feed but
not many gears!
[3] and a pair of half-ton machine skates for another two quid )

Dave H. wrote:
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?


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

"RBnDFW" skrev i en meddelelse
...

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

That coil is no more than 5A max at 12V.
But the peak pull current is higher round 15A.



--
Uffe Bærentsen

"RBnDFW" 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

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)

"Rules are for the obedience of fools, and the guidance of wise men" -
Douglas Bader