She hums but she won't spin - UPDATE

[Stuart Nelson]

I haven't turned anything in the last couple of months due to it beng so hot. The lathe was working fine when I last used it. Today, all it will do is hum. I checked the belt, blew out the capacitor with compressed air but no luck. Any ideas" It is a HF 34706 that I have had for 6 years with no problems in the past other than replacing the belt once.

[Rod Sheridan]

Failed capacitor or open starting switch would be the first 2 items I would check.........Regards, Rod.

[Ken Fitzgerald]

Stuart,

Without any thing on the spindle, turn it on and see if you can spin the spindle by hand and get the motor to start turning. Don't let it run long this way. Turn it off.


The humming makes one think either the starting capacitor for the motor has gone bad (opened up) or the centrifugal switch contacts in the motor has either gotten dust keeping them from closing or are damaged.

Be careful if you spin the motor up manually as I suggested.

[David Christopher]

turn it on and give it a spin by hand

[Dave Wagner]

make sure you didn't accidently engage the spindle lock if it has one.

[Stuart Nelson]

I tried turning it by hand...it will turn but does not start. I have a GE 3/4 motor...wonder if that could me made to fit.

[Stuart Nelson]

I spent some time this morning tinkering with the motor. I had tried turning it by hand to see if it would start and it wouldn't. Then I removed the belt so there was less tension and tried turning it again. It started turning very slowly and didn't speed up. I switched it off and on again and gave it a spin and it started spinning at full speed. So, is it the capacitor or the centrifugal switch?

[Ken Fitzgerald]

Stuart,

It could be either one.

The centrifugal switch puts the starting capacitor into the circuit temporarily.

Typically, what happens when you shut the lathe off, the centrifugal swith closes. This puts the starting capacitor in the circuit.

When you turn the lathe/motor back on, with the starting capacitor in the circuit, the motor starts in specific direction. Once the motor achieves a certain speed, centrifugal force causes the switch to remove the starting capacitor from the circuit.

It is not unusual for the switch to get sawdust in them preventing the contacts from closing when the motor is turned off. Thus the capacitor isn't in the circuit to start the motor when power is turned on the next time.

AND....

if the switch is functioning properly, the capacitor can lose it's capacitance by becoming an open circuit. Now, the switch is functioning but the capacitor will not charge properly and will not provide the phase shift in the voltage necessary to cause the motor to start.


In other words, either can cause identical problem.

[Jeff Nicol]

By not using the tool for awhile sometimes any dust and dirt can absorb moisture and gum things up. Look into the motor and make sure it is free of dust and bits. The armature could be crudded up and the the power is not getting to the windings of the motor as it should. Some times a good air blast and a tap on the starter (Light tap not hammer!) will get things going again. The same thing could be causing the switch to not allow full voltage to go through with dust and gunk in the middle of the contacts.

Time for a good PM of the machines to make sure everything is good to go.

Stay safe around the Electicity!

Jeff

[Fred Wood]

Stuart,
Look at the centrifical switch. Switch is held on motor shaft by a set screw. It tends to loosen up and switch will not work.

[Patrick Grady]

You have a 'capacitor start induction motor'. The motor has two windings, a start and a run winding. When 115 v power is connected, both windings should be initially energized. You are hearing the run winding 'hum' but it needs the start winding (along with its capacitor) to start the rotor turning. Normally, the start winding engages, along with the capacitor, for one second and then drops out because a centrifugal switch spins( or less likely, a little electronic black box) and opens switch contacts that take the start circuit out. Problem probabilities in descending order are a malfunction in the centrifugal spin switch, motor terminal wiring, fried motor start winding, failed start capacitor, or rust encrusted windings that won't let the rotor start. Start caps rarely fail. They are easily tested: Remove the metal capacitor cover and pull off the wiring, then short the terminals with a screwdriver to prevent shock to you or the meter, and then with an old analog -not digital- volt meter, set to lowest R1 scale and connect to the cap- good cap will swing the meter one way and immediately back. Reverse the meter terminals and a good cap will repeat the swing). As others have said, the most likely fail is the centrifugal switch. Tests for both require motor disassembly which is tedious but not difficult: mark position of all parts with a marker or scratch knife. I recommend against hammer taps because you want to nail the problem's cause, not prolong it into intermittent motor-start neverland. Good luck and hope you post your 'winding findings'.

[David Woodruff]

Replace the capacitor. stay with the original values. Purchase a US made, GE, Mallory, Cornel-Dublier. I put my money on the cap.

[David Woodruff]

Replace the capacitor, stay close to the original value. If you can purchase U.S. made; GE, Mallory, Cornel-Dublier. That is most likely the problem. Good Luck, let us know it works out

[Karl Card]

you can say that again.....lol

[Stuart Nelson]

$7.52 for a new capacitor and she's spinning again.

[Terry Murphy]

:oGreat save Stuart!

[Patrick Grady]

Good job Stuart. Please let us know the MFD value of the capacitor and which outlet had the capacitor in stock over the counter this morning?

[Stuart Nelson]

It had a range of 189 - 227 and was bought at CC Dickson a local parts house.