Grizzly Lathe 12 x 24 G4002 Start Issue

[Grandpop]

I have owned this lathe for about 6 years now, and think the PO may have it about same time. I can't actually find a serial number to know the year/age. I really do like the machine for the most part.

Was taking some roughing cuts today to hog down some 3" dia HRS stock to 2.5 dia as part of initial steps to make a bushing for the new Norton 3X bench grinder wheel (2.5 flange OD, .500 ID, 1.000 OD). Lathe was running perfectly normal. Thought my roughing was about at .030 over (where I wanted to be for the roughing cut), so stopped motor and measured the dia (correct). Set the dial indicator to measure the shoulder area, dialed it the compound to start roughing the 1.00 dia portion. The lather motor would not start with the selector switch lever, something just made a loud humming sound.

Turned off the power, unplugged it from the wall, plugged it back in, open the safety stop, powered the green button up, and tried to start the motor again. Nothing but hum. Tried forward, reverse, and even tried to help turn the chuck to ease the motor start load. Just hums. Finally held the start lever on and spun the chuck, which did make the spindle rum about 10ish rpm (I was running 600 rpm before) while humming. Lathe is against wall, so it took some effort to clear out under the base and get it slid out enough so I could squeeze behind it.

This is the inside of the control cabinet, the motor with what looks to be perhaps both start and run capacitors (?), and the motor tag.




Any idea of where to start checking/troubleshooting this setup? I can't reach the spindle rotation start lever and get to motor quickly to feel if that is source of the hum, but thinking the motor is the hum source. In order to be sure, I would have to keep it humming for about 1 minute to get from front start lever to back motor, feel the motor, and get back to the lever again to shut it off. Would that hurt anything further if it is actually the motor or capacitors?

Would the 150uf and 20 uf on the motor tag be the capacitor ratings? Any easy way to test them?

While I do my own wiring and electrical installations, I am buy no means an electrical guru.

Thanks for any suggestions,
Ted

 

[fitterman1]

Yes, Grandpop.
Discharge them first for your own safety.
Use a screwdriver across the terminals.
Using a multimeter set on capacitance
make sure their values fall within the stated tolerances.
Replace if outside of tolerance.

 

[fitterman1]

Try to minimise any humming to prevent any heating of the windings. You don't want to damage the insulation.

 

[silence dogood]

The 450uf capacitor is your start capacitor. The 20uf is your run capacitor. If the motor just hums, you give it a spin, and if it goes up to speed, then it is your start capacitor. If it don't run then it is your run capacitor. It sounds like both of them are bad. which can be hard to believe but possible. Take the covers off and look at them, if there is any cracks, leakage. or/and burnt spots. replace. You can also take an ohmmeter or if your meter has one on it, a capacitor check. Make sure the power is completely off, first.

 

[dirty tools]

Dirty switch contacts can cause low voltage reaching the motor
this can cause noise also

 

[silence dogood]

Dirty switch contacts can cause low voltage reaching the motor
this can cause noise also

Good point, Check the terminal lugs to the switch and relay contacts. On my lathe, I had one that was loose. A slight pull on the wire and the wire came right out. Replaced the lug and after that the motor ran fine.

 

[markba633csi]

Capacitors sometimes fail suddenly but I suspect something else. It's possible the motor's internal centrifugal start switch has failed, but there could be an open start winding in the motor. Check for loose terminal connections at the motor itself. They sometimes loosen up over time from vibration.
Most folks will tell you to replace the 150 uF start cap first and that's a good place to begin. If that doesn't get it going then you would probably need to pull the motor and do some bench tests
-Mark
ps You can do a simple capacitor test with an ohmmeter. You remove the cap from the motor, discharge it with a screwdriver, and connect the meter probes one way and then the other to the cap terminals. Each time you reverse the test leads you should see the meter give a low ohm reading which then rises towards high ohms. This will test the cap for shorts or opens; it won't tell you the absolute value, but if you get what appears to be the correct behavior the cap is probably ok.
This test applies to older meters that cannot read capacitance directly

 

[Mitch Alsup]

For a sudden failure, I would suspect the centrifugal switch over the run-capacitor.
{Actually any switch between the plug and the motor.}
I had a problem with my G4003G lathe when It arrived in that the forward/backward lever was not causing the power switch to engage at the right points. 20 minutes later after removing the switch cover and adjusting the cam, it was all good again.

Also note: Electrolytic capacitors don't hold a charge for more than a couple of seconds.

 

[Papa Charlie]

Make sure you have power on both legs coming out of the panel to the motor before you worry about the capacitors. I would venture it is in the panel. Check the output from the last source in the panel to the motor. If you have power on both legs then it is the run capacitor. If not, track backwards into the panel until you find the unit that is the cause. I can't remember if the starters have heaters in them or not. If they do, you may only need to replace the heaters, which wear out and not the entire switch.

 

[Grandpop]

Thank you for all the help!

I was afraid to keep trying things while it was humming. I got the capacitor covers off eventually; the top screw on the run capacitor was a bear - almost dropped the motor down, but with a 90° phillips driver and two fingers I was bale to remove it.

Looked at both capacitors, and did not see anything obvious. Noticed that one lug on each had obviously been hand soldered (unprofessionally), with other lug on each being a much higher automated solder job. Did not notice anything with the run capacitor when looked at it. Thought I might have seen some movement when I went to turn the start capacitor over, so played with it. Turns out the solder was not stuck to the lug - whole big chunk pretty much just hanging there (wire was making minimal contact with the lug. If it shows up in the photo, black wire right side terminal.



Got out the new variable temp soldering gun that I received for xmas, forced some soldering paste behind the chunk, then everywhere on the back side. Not sure it looks any better than the PO did, but the chunk is stuck back to the lug, and I re-inforced the back with more solder.



I do somewhat recall the PO saying that he had some trouble with what I remember him calling a contactor, but I thought he said he replaced it. So thinking that maybe he said capacitor and meant he had to re-solder it?

With that little solder job, it is running just fine again. While I was in there, I did slightly tighten the drive belts. And since I had the back control and side gear covers off, I took the rear splash shield off to finally flatten out the bottom chip tray after 6 years of it being bent. (don't ask, I managed to buckle up the sheet metal tray slightly thrying to jack the lathe to get the HF dollies under it). With your help, I learned something about the lathe, capacitors in general, and did some overdue maintenance. Not a bad day!