Help wiring drum switch

As far as whether you want a reversible motor on a threaded spindle lathe, my answer would be yes. You know not to try to do turning, facing or threading in reverse. But there are at least two scenarios where you must be able to reverse the spindle motor.

One is if you are ever doing OD grinding with the machine. The surface of the work piece and the surface of the grinding wheel must be moving in opposite directions. The way in which grinders are normally set up, the surface of the grinding wheel where it contacts the work is moving downward (so that the spark stream will be down toward the chip pan and not up towards the operator's face). And the front surface of the work with the spindle motor properly wired is also moving downward. So the relative surface feet per minute would be the difference between the SFM of the work and the SFM of the grinding wheel. It's never likely to actually happen but if the surface velocities just happened to be the same, the relative velocity would be zero and no grinding would ever be done. So the spindle motor would be put into reverse for any OD grinding.

The second one is if you are ever doing an operation where once the half nuts are closed and the lead screw is turning whenever the motor is running, you cannot open the half nuts for the duration of the job. So at the end of each pass, you stop the motor without disengaging the half nuts, back the cutter out with the compound, and reverse the motor to run the carriage back for another pass. The most common case would be cutting metric threads on an Imperial lathe.

There may be other cases that I haven't thought of.

Back to the drum switch wiring, Mark's thought that the red and black leads go only to the start winding and not to the start circuit could be the reason for the problem. the result would be that the start winding would always be energized. And will eventually burn up. The start winding is not intended to be energized all of the time that the motor is running and usually has fewer turns and smaller wire than the run windings. You should unplug the line cord and run the checks that Mark gave.

If that turns out to be the problem, you can still use the drum switch to reverse the motor but it does not have enough contacts to stop the motor in the OFF center position. Which means that if you do it that way, you must NEVER leave the drum switch in the OFF position because the main motor switch will still apply power to the run windings (only). And a few minutes of that will burn up the motor.
 
Agree with Robert above, the start switch and start capacitor would potentially be bypassed, not a recipe for a good-running motor. So you need to do the ohmmeter test
If it passes the ohmmeter test then you must still have something wrong with your external wiring
M
ps these motors don't instantly reverse, so you don't need to worry about that John. They need to come to a stop first, because of the centrifugal switch inside. If you flipped the drum switch from forward to reverse quickly the motor would continue running in the forward direction (assuming it's wired correctly)
 
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Thanks for your knowledge and suggestions. In looking over the situation and hearing from other friends on the matter too this is what I'm thinking about as a solution. Please give me any feedback, best part of this forum is access to your thoughts!

I think I'm going to take a little advice from several people here.

Several folks are rightly advising to be careful of a screw on chuck in reverse. Very good advice. Additionally I am upping the horsepower and that will lead to more of a "start up jerk" than the old motor. I know the flat belt will slip a bit but still more of a risk with higher hp.
That said, I still think I want reverse capability, and here is what I'm thinking about to make it a bit safer.

I did get the motor to work correctly using two switches, the rotary for direction change and a single pole switch for power.

I'm thinking of using the two switches, rotary and single pole. The single pole will let me use one of those industrial start stop paddle switches for power and that seems like it would work well up in front by the headstock. The rotary switch will control forward and reverse only and I'm thinking I will make a "reverse lockout cover plate" that would prohibit accidental hitting reverse without removing the plate. Then if I ever want to do grinding or metric threading I would have to take the extra cover physically off to use reverse and hopefully then be more mindful of the additional risk. The rotary switch would be located near the rear of the machine.

If you have any feedback give me your thoughts. As it is working out, I'm glad I had the wiring problem as it seems to have led me to a better and hopefully safer solution.

John V




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That sounds fine John, safety is a good thing
A simple hinged cover would work for the direction switch, something to focus your attention
I have a similar control for my small lathe
 
I will add one comment. You still do not ever want to leave the FWD/OFF/REV switch in the OFF position as the OFF/ON switch is still active. In this scenario, it would be safer with a 2-position FWD/REV switch.
 
Thanks, a good reminder. Thought I would make the "safety cover" so that it could only be in forward. Then make a label reminding myself , or successors not to have it in the off position when the cover is off.


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Actually, it shouldn't be in the OFF position ever. If it is and anyone turns the Off-On switch to the ON position and leaves it, the motor will eventually burn up. As with the Start winding disconnected and the OFF-ON switch in the ON position, the motor will have power on the Run windings but it will not start. That's why I suggested that the other switch should be only a two-position DPDT, not one with center OFF.
 
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