I've had a sticky centrifugal switch a couple of times

Had to start it by hand pulling the chuck and once my hand was clear… switching on

you grip one chuck jaw with a forefinger and flip the spindle

in the parlance of a 1930s lathe manual, "pull smartly towards yourself before switching on!"

I think it was a bit of dirt or oil, in one case it happened after oiling the motor bearings

It tends to blow my 5A fuse when it happens, so don't leave it switched on when it hums because the system is definitely stressed

Edited By Ady1 on 24/03/2022 00:12:37

If the capacitor is accessible, and the connections, it might be worth just replacing it, motor caps are cheap. Look at the data on the side of the existing one to get the right value and working voltage. Many suppliers have been mentioned here, for these even RS are reasonably priced. If that doesn't solve the problem then it's probably the centrifugal switch, but getting at that is harder. Ideally if you have to take the motor off you might consider replacing it with a 3-phase + VFD…

Do Chinese single phase motors have a centrifugal switch ? The capacitor may be permanently connected (PSC).

Does the machine have forward / reverse capability – if so, maybe look at the reversing switch / contactor arrangement.

Nigel B.

I had exactly the same issue with my BH600G before I bought it. The short answer was a loose connection in the control box. After tightening all the screws on the contactors the motor started up normally.

First are you sure it is the motor, when applying power to the lathe, if all the safety switches are closed you get a clunk as the main contactor closes. No clunk then a safety switch is open. There is a small hum from the 24V transformer all the time.

If I remember right (ref pg 65 of Grizzly manual) the problem was the overload contactor FR had worked its way loose from KM1 (top left)

FR hangs under KM1 and is held in place by being screwed into T1, T2 and T3 on KM1.

In normal operation K3 (top right) closes, then for Fwd/Rev KM1 OR KM2 close. For testing, it is possible to push the centre of KM1 OR KM2 and start the motor.

The motor has connections U1, U2, V1 and V2. In the control box U1 = Neutral and on KM1 T1 = U2, T2 = V1 and T3 = V2

When running Fwd

U2 = Live

V1 = Neutral

V2 = Live

When running Rev, V1 and V2 are reversed.

U2 = Live

V1 = Live

V2 = Neutral

BTW It does not like starting from cold at a high spindle speed, releasing the belt tensioner lets the motor spin up to speed first.

Hope it helps

Adrian

As you say the motor hums, so its not the machine wiring, its the motor. As others have said try the string idea but be very very careful. By using the string idea you are eliminating the motor start winding, the capacitor and centrifugal switch and if the motor runs then one of those three are faulty. I haven't seen one your type lathes, but the motor is available then a capacitor change might be the easiest to do. For test purposes ONLY and with slack vee belt, two old 5 foot fluorescent light capacitor connected in parallel will be OK in place of the original one, after all that its a strip down. If you send me a PM with an email address I 'll send you more details. John

Couple of thoughts ?

Humming could simple be a cooling fan (or invertor if fitted)

Checked all fail safe interlocks or emergency stop button(s) they can be problematic sometimes

My cheap bench drill failed to start in the same way and it was due to the under rated capacitor failing; it had a 250v capacitor but for reliability it needs to have a 380v rating .the replacement capacitor is a little bigger and required a larger housing as it is in an exposed position. The original just lasted the guarantee but the replacement has worked for many years. Colin

A capacitor may fail for reasons other than voltage rating. I had a 240V induction motor that was fitted with a starting capacitor that had a much lower working voltage rating, about 120VAC if I recall correctly. This seemed low, but on investigation I found voltage across the capacitor was always considerably lower than the supply voltage, presumably due to inductive reactance of the winding.

Michael,

I had a similar issue with my Chester Crusader. I got through few caps before giving up and going to Newton Tesla VFD set up.

all I can say is that I wish I'd done that the first time I had a trouble!

Totally transformed the lathe.

Good luck and I look forward to a further update once its all up and running with the VFD.

Jim