Reverse mill with VFD or mill switch

kplyler

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I have a Bridgeport J-head knee mill clone from Taiwan "Cut King" (Mid 1970s I think, if anyone has any information on these I would be interested). Anyway, I plan on my first power tap experience. I have a VFD with a reverse button, which I have used a few times. The mill also has a yellow switch up high on the left with three positions Rev-off-Fwd. Its always been in the forward position since I bought the machine a couple years ago. I did test it when I first got it, and the Reverse option works.

My question is when I power tap, should I use the off, reverse buttons on the VFD or the Rev-off on the mill. I'm concerned with the health of the Mill and VFD. Does changing the mill from Fwd to off, and then Rev pose a power issue for the VFD, over loading it? Does switching the mill cause undue stress on the Mill, and its better to switch via the VFD?

I'll likely do some experiments and see which way slows down the quickest in order to change directions.

Thanks for any comments.
 
Most VFD makers make it pretty clear in their handbooks that NOTHING should be between VFD and motor except a suitable cable or a load inductor, but you should be able to use the existing switch to run the forward and reverse control voltages into the VFD logic inputs.

Dave H. (the other one)
 
+1 what Dave H said.

To reiterate, if that switch is wired between the VFD and the motor, do not move it with the VFD powered up. There should be no switch between the VFD and the motor. It is possible to wire the switch to the VFD logic. We'll be happy to help you through wiring changes if needed.

For power tapping, I have my VFD set to 3 second decel, works just fine, but you have to think ahead a bit.
 
Thanks Dave & Jim, I did not know there should not be a switch between the VFD and the motor (but that was what I was concerned about). The manual does not say anything like that that I can find, but it makes sense. The Mill came wired with the VFD (Huanyang hy03d023b) . I had not thought about using the Mill switch as the external switch on the VFD. I checked the VFD manual, and it does support several external switch configurations for fwd-off-rev. So it should not be a problem wiring the Mill switch as that switch. that will make using the VFD much more convenient (the VFD is currently affixed to the back of the mill).

Thanks
 
No problem - and consider adding a braking resistor* (assuming your VFD can use one) if you want a really rapid stop for power tapping - a mill's spindle should be much easier than my lathe's spindle and 10" 4-jaw full of steel...

Dave H. (the other one)

*OEM will probably be expensive, but some Chinese Gents advertise them on EvilBay, just check the resistance and power handling in the VFD manual
 
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