WM14 from WARCO

[Hopefuldave]

HS93 Wrote:I thought that at first so I turned it off via the plug not the switch just to see if it stopped the same, and it does also the main casing gets hot this has been a problem on the Grizzly G0703 that shares all the same head components except it has a 600w motor instead of a 500 w on mine.

Peter

Hi Peter,
mine stops on a sixpence too, particularly if I have a small tool in the spindle (e.g. a Clarkson-alike quicklock chuck and 1/2" endmill), less so with a big heavy fly-cutter (I've made mine quite hefty, a 6" disc of 1" cast iron from and old chuck backplate and a 2 Morse blank... it seems to calm the chatter down!) or something similar with quite a bit of rotary momentum.

I'm not sure, but there may well be an anti-parallel diode on the motor side of the speed-control which would do two things: it'd absorb spikes generated by the motor when the speed control shuts off (winding inductance tries to keep the armature current going, there's no path for it, so it behaves like an ignition coil - not nice for the semiconductors that tried to stop the current!); and it would also shunt the motor-generated EMF and brake the motor, whether you switched off at the stop button (which on mine just cuts the mains to the electronics, yours may differ) or at the wall.
It'd be interesting to compare the behaviour with one of the DC-motor mills with a forward/off/reverse switch, as that would I think disconnect the motor from the controller?

Bigger machines would probably have a dynamic braking resistor to absorb the stored energy (I have one attached to my lathe VFD - gets quite warm after a few stops with the big chuck), but it's possible the board just dumps it into a hefty diode? Thinking about this has got me worried that my big fly-cutter may push the diode too far...

That's the absolute minimum I'd do (anti-parallel diode) if I were designing it, based on some time working on *big* DC servo systems in a past life!
Does yours have the American KB speed control board or a Chinese "tribute to", as there may be some big differences?

Anyway, there's not a lot of momentum in the motor/gears/spindle so I wouldn't expect it to carry on spinning for long, particularly with the expected friction from the gears added in? Most gear trains are between 70 and 90% efficient, so for a 3/4 HP motor anything up to about 1/5th HP could be dissipating in the gears? That'd stop it pretty quick, and warm up the headstock a bit!
The Chinese DC-motor variable speed lathes I've seen in action seem to stop pretty quickly too (despite having perhaps a 6" chuck spinning at 1000 RPM!), and I guess they probably use the same / similar speed controls...?

Dave H. (the other one)