#5 Hi speed problem

Hello, I have a newly aquired #5 M1740 lathe. I have it wired in and am having a little trouble. The low speed on the motor works fine. When I try to hit the HI speed switch the contactor block from insinde the cabinet makes a horrible noise. I took the cover off of the contactor and watched it as the HI switch was hit. It almost looks like the contact patches won't stay closed. I sanded all the corrosion off of the contact pathces but it still didn't help. The motor is starting to turn over when the switch is hit but the contactor won;t stay closed and needless to say doesn't start the motor. Any help or suggestions would be greatly appreciated as I have a job to run on it soon.

I know this probably isn't the answer you'll want to hear, but if worse comes to worse, you can always run the job on low motor. In fact, I almost never use high motor with my #5, as low covers most of the speeds I'm looking for on a big lathe.

Still, if it were mine, I would want it fixed. Good luck !

Hi, sounds like the same problem I had with mine.
After a little study of the motor wiring I decided that the problem was a weak coil on the starter. I can manually start it in hi speed using a block of wood to lift the linkage up on the hi speed side of the starter. I'm going to replace either the coil or hopefully the complete (very old) starter assembly sometime, but this got the job done for a while. Lots of potential hazards to consider before trying this, think about it first !!! Amazing old machines, still doing the job after 60+ years. Jim

Do this with the power OFF

Check the contactor by manually pushing the contacts together to make sure there is no linkage or mechanical problem. With mechanical interlocked contactors the linkage will wear and may develop wear spots that the linkage binds and the coil cannot overcome the added resistance of pushing the contact block upwards.


The coil of the contactor is pulled in and held with a latch circuit. On the contactor you will have the three main motor wires,also will have small wires that are doing the control circuit. In line with the three main contact blocks there will be a smaller (usually) set of contacts that "hold" the voltage to the coil.
If these are not making the contactor will chatter,buzz, rattle etc. and in your case not hold the main contacts tight. Do a check of all the small wires to make sure all are tight and well terminated. If all checks out then a meter is going to be a must to verify that the coil is actually recieving the correct voltage. Say the coil is 120 volts, if you are getting 90 then the coil will not be strong enough to pull in.

Also check the control transformer. It may or may not have multiple connections for the different incoming voltages. Make sure the correct tap is being used for your voltage. Otherwise you can get low output fron the control transformer and even though the low is working the high just doesn't have enough voltage to operate.

Start with this and let us know.

And while jljim uses a wood block I would strongly advise not to follow suit.

Good reply from Mw Tech, understanding the system and carefully following a logical path is always a good approach. Jim (also PM for Dan)