Switching to Reverse with Lathe Running

[Bob Bergstrom]

Just noticed Nick Cook demoing the Powermatic 24-32. He throws the switch to reverse while the lathe is running in the forward direction. Does anyone else do this? Isn't it hard on the motor. I would suspect that because he was turning a small spindle he could. I am sure too much resistance would kick in the override and he would be pulling the plug to reset the speed control. I have a 3520 and always shut it off before changing directions.

[Roger Chandler]

I just think it makes sense not to chance a short out on an inverter or motor.......I always shut the lathe off before reversing!

[Gary Max]

Remember it's a 3 ph motor---- it doesn't hurt anything.

[Mark Hubl]

What you do in a rent a car stays in a rent a car! From what I have seen Nick prides himself on speed, so this is probably just some more schtick.

[Baxter Smith]

I have done it a couple of times by accident and often wondered what effect it might have.

[Faust M. Ruggiero]

Most variable frequency drives allow you to do that. I do it all the time with my 3520. The lathe slows down and stops then reverses. Oneway lathes also work that way. Of course, I only do that between grits when sanding so I don't do it with a heavy blank. That would be tempting fate.

[Dennis Ford]

It does not seem natural to be able to do this but: as Faust wrote; it is not really a problem with most variable frequency drives, they use the programmed acceleration/deceleration rate to slow down before speeding up in the other direction.

[Fred Belknap]

Mine just goes off when I switch direction, have to hit the on button to get it going.

[Norris Randall]

In 195? I got a tour of a mfg. plant in Toccoa GA. Robert Gilmour LeTourneau built earth moving machinery. One of the first exhibits was a display of an electric motor inside a glass enclosure. A pump was turned on to start a heavy spray on the motor. Switch was thrown, motor had a large metal "flywheel" with a painted mark. The switch was thrown and in a "split second" the motor was up to full speed in the opposite direction. Those motors drove individual wheels on one of the first huge "drag pan" earth movers.

I also remember the guide saying, GE and Westinghouse had said "it could not be done"

[Richard Jones]

Ditto to what Faust said. Only when sanding.

As an addendum, I also reverse the lathe when removing chucks.

[Russell Eaton]

I bought a 4224B that Nick did a demo on. I asked this very question of him and his response was it is not a problem. I have done it a couple of times and the motor slows at a faster rate then reverses and starts back up. I still try to cut it off first then reverse, it just seems like the better way to me.

[Steve Schlumpf]

I did it a few times by mistake with my Jet 1642 and no problem but I wondered if it would hurt anything. When I picked up my Robust, I asked Brent English that exact question and he walked over to the lathe and actually demoed how it brakes the lathe speed and then ramps back up in the opposite direction. The vector drives are designed to be able to do that! The only time I use the reverse function is when I am sanding the form. I know it will work on large heavy blanks because I have done it - just to prove it could handle the mass... but the only time I actually want to reverse the lathe is when sanding.

[Faust M. Ruggiero]

Steve,
Being the lazy and technology whacko that I am, I also use it to insert and remove the buffing wheels on the buffing system. Richard, I am always worried I might catch a finger in a chuck when removing or inserting so I don't do those under power.
faust

[Steve Schlumpf]

Now that you mention it, I have done that with the buffing wheels but my biggest use of the reverse function is when sanding.

[Dale Miner]

Be sure to have the chuck set screws set to lock the chuck on the spindle before doing the reverse thing. Not much fun to have a heavy blank and expensive chuck flopping about and landing on the floor (or your foot).

[Richard Jones]

Faust,

You're probably smart not to. I've just gotten in the habit of loosening the chuck, hitting the reverse switch, power on at low speed, remove the chuck, hit the forward switch with my right hand as I'm hanging up the chuck with my left. If my lathe was situated differently with regards to my chuck storage, I probably wouldn't do it.

[David Gilbert]

While at the AAW Symposium in St. Paul in 2011 I asked the Jet representative about this very issue. I have a Jet 1642 and the controller on the Powermatic is essentially identical. He told me that it was designed for this. The motor decelerates on the profile set by the controller and then restarts in the other direction. I do this all the time while sanding. I tried reversing the drive when removing a chuck and snagged my hand in a way that told me that this wasn't a good thing to do. A rotating chuck removes lots of skin......

Cheers,
David

[Tim Rinehart]

While at the AAW Symposium in St. Paul in 2011 I asked the Jet representative about this very issue. I have a Jet 1642 and the controller on the Powermatic is essentially identical. He told me that it was designed for this. The motor decelerates on the profile set by the controller and then restarts in the other direction. I do this all the time while sanding. I tried reversing the drive when removing a chuck and snagged my hand in a way that told me that this wasn't a good thing to do. A rotating chuck removes lots of skin......

Cheers,
David
I've watched some folks do this, either installing or removing a 4 jaw chuck...and admittedly, I've tried. I then started thinking about a finger getting sucked into the hole for the chuck key, and that pretty much took me back to manually installing and removing 4 jaw chucks.

[Jim Burr]

Steve S and I had this very conversation a few months agoafter I had hit the switch accidently. We both came up with "Dunno".I called Jet and got the same answer as David...they are made to do that.However!!...to prevent your wife from opening your ketchup bottles...I only doit on sanding and get your hands out of the way!!!

[curtis rosche]

Ive done that on my lathe, if i dont wait for it to slow down enough, the start cap doesnt kick in so it just keeps running in the same direction. as it slows down i can make it switch directions though.

[Robert Edington]

It shouldn't hurt a thing???? Where does that energy go? It goes to the sand resistor. The sand resistor is that aluminium rectangle thing mounted in the head stock. It will get hot and eventually burn out and can catch fire. Mine did. It is not a good thing to see smoke coming from your 3520 head stock. Powermatic was no help. Delta Electronics helped me get it fixed. I was not changing directions. Just turning it off and on many times while turning a small paper weight. The sand resistor absorbs the energy (heat) during motor braking.

[Dan Hintz]

I can't say I've ever heard anyone use the term "sand resistor". It's a ceramic power resistor with an aluminum heatsink, should anyone go looking for a replacement.

[Brian Myers]

There are motors rated for instant reverse so it would depend on the motor . My brothers SouthBend 9A metal lathe came with a Daytona that is rated instant reverse. I have also done it on my wood lathe by accident , bad placement of the reverse switch on my part, and the lathe just reverses with a bit of a jolt.

[mark ravensdale]

The very day I got my nova dvrxp I tried the reverse function only to have the chuck unscrew itself and land on the bed of the lathe, was mighty happy I didn't have a 15 by 8inch chunk of laburnum attached at the time as I can't run as fast as I used to :)