South Bend 14" 'Fourteen' Speed Control Wiring Diagram ? Convert to 1ph motor ?

I have run into a problem. The local electrical company refuses to upgrade my shop to 3phase, despite the fact it is run through my area and that it runs on lines that run through my property.

The South Bend Fourteen I purchased is the gear head, belt drive version with an electronic speed control. I have been told by someone who owned a few of these lathes that the electronic speed control it is not compatible with a VFD or Rotary Phase Converter. He says that you get very erratic and very inaccurate speed readings off of either VFD or RPC, and that you will eventually burn up the speed control.

I have taken the lathe to a friend's shop that has three phase and we spent quite some time getting it wired up today, and I have found that if the lathe is powered with a steady supply of 3 phase- the speed control works and remains very accurate.

However, powered by an RPC- the speed control was off- the reading on the tachometer on the lathe's control system does get off by quite a bit. So that much is true.

I was told, however, that if I could find a wiring diagram for my lathe, that I might be able to switch the motor over to a 2 or 3 horsepower 220v motor.

I contacted Grizzly to purchase an idler gear for this lathe, and what I got was not an idler gear for my lathe, so I am reticent to trust anything they provide. If anyone owns this lathe and has the wiring diagram for the speed control, or could advise me on how to keep the electronic speed control while converting to a 1phase electric motor, I would be VERY greatful.

I

I have wiring diagrams for the 14"
And idler gears
And tailstocks
.....
Ted
[email protected]

SBLatheman said:

I have wiring diagrams for the 14"
And idler gears
And tailstocks
.....
Ted
[email protected]

Click to expand...

And belts...

Seems to me it might be a whole lot easier to just get a VFD controller for it and by-pass all of the old speed control stuff. The new VFD will have all the control features you could ever want and none of the issues of old electronics. You may be able to use some of the old switches and pushbuttons so long as you do not wire up a system which connects or disconnect the output from the VFD as the "start - stop" mechanism. The manual that will come with a new VFD will give you lots of information about what can and cannot be done to control the motor.

Of course, this assumes that you want to run the lathe and not to make it into a museum piece. If it's a museum quality restoration you want, you'd probably be best off to get a rotary phase converter which will generate "real" 3-phase power and which should make your machine happy. It is, however, an expensive solution.

vandis said:

Seems to me it might be a whole lot easier to just get a VFD controller for it and by-pass all of the old speed control stuff. The new VFD will have all the control features you could ever want and none of the issues of old electronics. You may be able to use some of the old switches and pushbuttons so long as you do not wire up a system which connects or disconnect the output from the VFD as the "start - stop" mechanism. The manual that will come with a new VFD will give you lots of information about what can and cannot be done to control the motor.

Of course, this assumes that you want to run the lathe and not to make it into a museum piece. If it's a museum quality restoration you want, you'd probably be best off to get a rotary phase converter which will generate "real" 3-phase power and which should make your machine happy. It is, however, an expensive solution.

Click to expand...

I tried it with 2 RPC's- the Varispeed and tach were both "off". Running slower usually that what appeared on the display and speed setting.

I'll keep it in mind about the VFD conversion, I just hate to junk everything.

I have to ask: Is the issue that the lathe spindle does not turn at the RPM you select from the speed control? Is it off by 50%? Or is it off by 10%?

I did a little bit of looking and it appears to me that the variable speed mechanism consists of a Reeves drive with some sort of servo system to actuate the pulley system inside the Reeves drive. If that's the case with yours, then I would not be surprised if the the spindle speed did not exactly track your command input into the speed control. If you've ever looked inside one of the older Reeves drive systems, you'd be either amazed or horrified at what you see. Many of them follow the design principle of a snowmobile type belt and pulley system except that instead of a rubber belt, they used a belt made up of wooden blocks with little leather pads on the ends of the blocks. They actually worked quite well but so far as providing accurate speed control---probably not.

In your case, I think you could easily use a VFD to handle the single phase to 3 phase conversion. Then pick some intermediate speed setting on the Reeves drive and take off the mechanical/electrical servo control system and just vary the speed of the drive motor with controls provided by the VFD. If you HAVE to know the actual spindle RPM then you should be able to make yourself a little table relating VFD setting to spindle RPM. The VFD is going to track motor speed much more closely than changing the pulley positions inside the Reeves drive.

Again.....museum piece that needs constant attention or functional lathe that can make stuff?

A reeves drive gives you real mechanical advantage, unlike a VFD, which loses power with decreasing RPM. I would be inclined to keep the Reeves drive if possible. So the question becomes- what exactly is the problem. If the machine runs well, and covers the speed range desired, but the tach is not correct, then I would add an external tach, or go without, its not that big of a deal. If it has some sort of feedback to attempt to maintain speed, I would disable that

allan