Lazy Lathe Motor Blues

Several Forum members were very helpful when I was trying to wire up a fwd/rev switch to my lathe motor. Everything worked out well, but now I have a new problem. After selling my old Atlas I set up the same motor to work on my new lathe. All I had to do is shorten the wiring & shielding from the switch to the motor, & reverse two wires (per data plate) to make the motor start in reverse, since the motor pulley was oriented opposite the way it ran originally.
Everything worked fine until I put the belt on the motor pulley. It turns out if there is any load on the motor pulley at all, the motor hums & it will not spin up. Give the belt a good tug; either forward or reverse, and the motor takes off. It seems the capacitor start is not kicking in. I thought I may have inadvertently reversed some wires, but nothing seems to change the equation. I replaced the motor-start capacitor, but that didn't help either. I was told there is a relay or switch inside the motor. If anyone has experienced a similar difficulty or has any thoughts on what I can do to get this thing working right again, I would appreciate your input. It is a very clean, almost new motor, and ideal for my purposes, so would hate to dump it if it is a minor problem that can be fixed. Thanks!

Hi There,

My "gut" reaction is that there is something wrong with your wiring hook-up. If everything was working properly on the other lathe, then something when wrong when you changed it.

Most single phase induction type motors use some kind of switch to control the start windings. Usually this is set of spring contacts on a circuit boad mounted in the end bell and a centrifugal device on the rotor that controls these contacts. At rest, the cotacts should be closed and when the motor reaches approx. 80% of its rated RPM, the centrifical device forces the contacts open. If you have been under the cover plate on the end bell swapping wires, it is possible to misroute a wire so that it gets in between the contacts but this is pretty unlikely.

Double check your wiring.

-Blue Chips-
Webb

[ 12-16-2004, 01:30 AM: Message edited by: Webb Wyman ]

Thanks Webb. Was kind of thinking the same thing. I will hook it it up w/o the fwd/rev switch; just the two leads for 220v. Depending on the result, may try it set up for 110v. I know I used to hear a distinct "clack" when the centrifugal switch cut in to spin it up, and again when releasing as the motor was powered down. That is no longer the case. I hope to avoid pulling the housing off. I can just envision spring-loaded parts pinging & flying this way & that, resulting in a nightmare figuring out how to put it all back again!

Hi There,

Go ahead and test your motor w/o the drum switch and see if it is working properly. If you decide that you need to remove the end bell, Don't Panic! Unless something is broken, nothing is going to jump out at you. The centrifugal switch is very simple and pretty foolproof. They can wear out but it takes a lot of starting and stopping to do that. They usually last a lifetime.

If you decide to remove the end bells, I will give you a couple of tips. Before you unbolt the end bell, scribe a line from the end bell to the case. This will help you realign the end bell when you put it back together. Do this to both end bells. Also, next to the scribe alignment line, take a center punch and place a dimple mark on the end bell and the case. Use one punch mark for the front of the motor and two punch marks for the rear. This will aid in preventing you from confusing which end bell goes on which end.

I hope this helps. Good Luck!

-Blue Chips-
Webb

pwcosol,

Try vacuuming out the start switch end. I had the same symptoms on a table saw motor and discovered the start switch was plugged with sawdust and would not make the contact needed to start the motor.

Stu Miller

Thanks Webb & Stu for your thoughts. I spent most of yesterday working on that motor. I removed it from the switch, and ran it directly from the power source after verifying I was getting 220vac.
Despite relocating the leads, it still failed to kick-start up. Tried it wired for 115vac w/same result. After pulling off the front & rear bell housings, I saw what a simple arrangement it was. Attached to the rear housing was the lead terminal board. Arched across this was a wide, slotted copper band, which terminated in a contact point set-up w/one of the start winding leads to the capacitor. On the end of the armature was the centrifugal switch. Seems there is a phenolic ring around the armature shaft, and if the ring is forced forward it forces out the two arms of the switch. A set of return springs must withdraw the arms when the centrifugal force
is reduced. Am still not sure just how this thing works, but I imagine somehow that copper band forces the phenolic ring to open the cf switch and the field generated by burst of current from the capacitor spins up the armature quickly.
Anyway, I looked @ everything & saw nothing obviously broken, missing, shorted, open, etc. Did a few continuity checks which were good. I cleaned the contact points & anything else that needed it, but there was very little dust or grease. Slapped it all back together, ran an op-test, & still no cigar! I noted when powering up, the motor will start off slowly for the first two or three seconds (so long as there is no load on the pulley). Then I hear a slight "click", and it takes off. I noted the motor to "jump" a bit on the workbench when this occurred. The end result was I mounted the 3/4hp Baldor to my lathe. It was already set-up w/a fwd/rev switch, running 115vac. Just got to shorten the wiring & shielded conduit from the switch to the motor. When you throw the switch on this baby, it takes off like a bat out of hell! It will do until I find another smaller motor down the road.

Hi There,

I'm sorry you were not able to get the motor working. But at least, maybe I can enlighten you as to how the starting circuit is supposed to work.

The circuit board with the copper ring and contact points IS the centrifical switch. The phenolic ring with the spring loaded counter weights controls the Openning of the contacts on the copper ring.

When the motor is "at rest," the springs on the counter weights push the phenolic ring against the copper ring; forcing the contacts closed and completing the circuit for starting the motor.

Turning "on" the motor, electrical power flows into the "run" circuit. Also electrical power flows through the contacts, up to the start capacitor and then through the start windings. This provides the torque the motor needs to start turning (this is why this is called the "start" windings or coils or circuit).

When the motor spins up to a pre-determined speed (about 80% of the motor's rated RPM) the centrifugal forces on the counter weights becomes sufficient to overcome the return spring tension on them and they swing out. As they swing out, they pull the phenolic ring away from the copper ring. The copper ring moves away, causing the contacts to open; thereby switching off the start circuit. Electrical power continues to flow through the run circuit; so long as the motor is on.

As to the "slight click" sound you hear, I am unsure. Does your motor have some kind of thermal protection? How old is this motor? Is it an instant reversing motor? Depending, there may be other devices inside the motor that are at fault.

Some motors are built with a thermal overload device that cuts off power to the motor if the electrical draw is too great for too long (to prevent burning out the motor). Most were made by Klixon and are found in two basic configurations; manual reset (a red button sticking out of the end bell) and automatic reset (no button). The latter type sometimes get sticky and don't reset properly. Sometimes they will reset at weird moments.

Instant reversing motors (single phase) will have a relay inside connected to the start windings (in addition to the cetrifugal switch). This type of motor is rare and expensive but were used in machine tools sometimes. This relay can go bad. Did your motor have a mysterious black box inside it?

My last thought on the "slight click" noise is an electrical arc created because of a bad connection somewhere in the start circuit. This could be inside the capacitor. Are you sure the capacitor is good? Did you test it? I think I read that you replaced the capacitor. Did you use a new one? Is it the same capacity? Start capacitors are the electrolitic type and should not be energized for more than 3 seconds. Otherwise, they will deteriorate. Considering all the testing and experimenting you have been doing, it may have gone bad.

Just some more thoughts for your contemplation. Good Luck!

-Blue Chips-
Webb

Again, thanks for your input, Webb. Regarding your questions, the slight "click" I heard sounded like the the metal "wings" or flaps returning to position. I recollect the sound they made when I was operating them manually while the motor was apart. I replaced the capacitor with a new one of the same voltage & mfd rating as was supplied originally. The motor was made by "Ajax", and is not thermally protected. There were no other elements inside nor outside the motor. I appreciate your description of how the motor operates. I have a book on electric motors by Audel and another on electricity, but neither really helped me to understand what takes place when the motor (mine specifically) is energized. Now I have somewhat of a grasp of the chain of events. Will keep that little bugger on my spares shelf until I decide to take another whack at it (perhaps with a BFH !!!).

Hi There,

Based on what you said in your last post, it sounds like the centrifugal devices is sticking. Hence, when it "clicked," the centrifugal device snapped back into position and consequently forced the contacts to connect and allow the motor to start.

If you get ambitious, you might tackle the Ajax motor again and see why it is sticking.

Good Luck!
-Blue Chips-
Webb

I recently had a similar problem and after ohming the start windings(from "line" connections), I found that I was misinterpreting the diagram and current was not going thru the centrifugal switch and on to the cap.

Considerable head scratchin' and more coffee was required. Discovered that one of the terminals on the "board" only went to another male spade terminal and not the switch.

Corrected that connection and it worked. I have rewired many such motors and this was an oversight.

Might be worth a look. Let us know what you find.

Rick