View Full Version : Worst That Could Happen

12-04-2003, 01:53 PM
I've been informed that repeatedly starting and stopping my lathe may do damage.

I have a Grizzley 13 x 40, one of the operations that I do quite often is to center drill small bar stock on each end. Needless to say this does not take long for each part, so there is frequent starting and stopping. Sometimes I may need to do 10 sometimes 25 or 50 in a row.

Am I damaging my lathe? Understanding electricity and electric motors is a shortcoming in my machinery education I'm afraid.

What could happen?

12-04-2003, 02:14 PM
The lathe doesn't really care. The motor does.
Most motors are fan cooled, and rely on running for some period of time to allow the fan to cool the motor. Repeated starting and stopping will cause a heat build up from high starting current without allowing time for the fan to cool. Worst case is cooking the motor windings and eventual failure.
Remedies can include replacement with a high duty cycle motor, or installing a clutch to allow the motor to continue to run while doing repeat operations.

12-04-2003, 08:18 PM
Also a collet chuck that opens and closes while the lathe is running. These are expensive ,but well worth it if you do a lot of parts.

12-04-2003, 08:26 PM
An electric fan circulating air through the motor might help.

12-05-2003, 02:33 AM
Fatigue in the motor windings, from repeated rapid heating, even from cold, is a big cause of motor failure. Repeated starting of a hot motor is worse, as temperature rises not only flex wiring, testing the integrity of the insulations, but also make the wire approach, and exceed, the smoke release temperature. Also the start switch will give out from excess heat at it's contacts. The bearings, if sleeve, like most found in a car engine, need to form the lubricating film of oil by rotation of the shaft, before the shaft is separated from the bearing metal. During this initial time, bearing and shaft wear is very high. It could be reasonable to figure motor life based more on the number of starts, than on hours of running. Overloading, and running at reduced rpm, of course are obvious killers.

[This message has been edited by darryl (edited 12-05-2003).]

12-05-2003, 12:30 PM
I fried amotor on a second op machine. SO at that piont I put an electric clutch between motor and drive pluse a pancake fan on the motor coweling .


Forrest Addy
12-05-2003, 03:03 PM
You're jumping at shadows unless you're starting and stopping the machine evey minute for hours on end. The lathe will take it without a qualm but the motor may not like it.

Motors can be started and stopped across the line so many times an hour depending on the inertia and load. A 1 HP motor starting a lathe in back gear has an easier time than if it started a lathe in highest RPM with a big chuck having a massive but centered piece in it.

If your motor is equpped with a thermostatic snap action switch bonded to the stator iron, it's practically burn-out proof but the start switch and the capacitor are another matter. They have a finite life.

Remember Grizzly motors are Asian built at low cost. I don't know about present day Grizzly motors but up to a couple of years ago the factory would omit the vital last step of dipping and baking the assembled motor stator. The windings while tightly laced were still able to buzz and chafe in proportion to current. over time the insulating varnish would wear through and short causing a progressive fry of the motor. Take your disassembled stator to the motor shop and have them check it out. My local shop only charges $20 for a dip and bake if I do the clean-up.

Single phase motors are delicate compared to three phase. A well built three phase motor can be started 10 times a minute indefinitely with no shaft load except its own inertia.

If your livelihood depends on that motor plan ahead for eventual failure. Keep a replacement on hand.

http://dealerselectric.com/ offers a 1 HP VFD motor combo for $290. With the programmable accel/decel and current limit there is no way you could fry a motor on a VFD no matter how many starts per hour you demand of it.

12-05-2003, 07:17 PM
Thanks for all the input. I think Forrest has the best answer for me. I'll plan ahead for the new motor. Just in case.

Hopefully it won't come to that as I only need to keep this lathe this active for maybe another year, then I hope to be able to replace it with a Mazak or a leblonde. That's the plan for now anyway.