# Upgraded lathe to 3phase VFD



## Tciplumber (Jun 14, 2013)

I had bought a new Grizzly G4003G gunsmith lathe in January and added a DRO from DROPROS.  I was extremely happy with the accuracy and performance of the lathe with one small exception.  The slowest gear spindle speed is 70 RPM.  That's no problem until trying to cut a coarse thread up to a shoulder; when slower speeds would really help.  I had a 2 hp VFD, and a friend gave me 2 hp motor with the same bolt pattern.  I had to make a double sheave pulley to match the OEM pulley, as the shaft sizes were different.  I removed the entire control wiring from the back of the lathe, and pretty much didn't use any of it. (anyone need chinese electronics?)

It took about 5 hours to switch everything over.  Did a little rewiring to make things more user friendly.  I used a contactor with the OEM start / emergency stop buttons and power lamp to provide power to the VFD.  This starts and stops all power to the lathe.  Since you can't put disconnects between the VFD and the motor, this gave me a good way to emergency stop the entire lathe.  

I used the forward/reverse switch on the carriage to issue forward or reverse start/stop commands on the VFD.  I removed the "inching" button from the lathe control panel and replace it with an industrial potentiometer so that it would look factory.  A few new decals, and the control panel looks like it was issued that way.

Now I have variable speed at nearly full torque from nearly stop to full speed in every gear range.  Now I can cut a 4 TPI thread up to a shoulder nice and slow with no fear of crashing the tool into the workpiece!

What has impressed me is how much smoother and quieter the lathe runs.  The "normal" gearbox noise is gone.  Without the carriage drive running, it is nearly silent.  

The BIGGEST benefit has been the surface finish.  I am getting near grinder finishes with carbide insert tooling at 360 rpm.  It's almost unbelievable.  The debate about 3 phase machinery running better than single phase equipment seems to hold a lot more merit now!


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## Hopefuldave (Jun 16, 2013)

Nice job, TC, and it sounds like you've discovered why industrial machines are usually 3-phase - the power delivery comes like a V8 instead of a twin!
Re inching, I put a TIG torch switch on my lathe's forward/stop/reverse lever wired (eventually) to the fixed speed inputs on,the VFD, and programmed it for 5Hz, so get 1/10 spindle speed (1/12 in the US, I guess?) forward or reverse for setup use, I've found that pretty useful. One can go a bit OTT on the control side, how about.linking a slide potentiometer to the cross-slide to ramp up the rpm when approaching the centre, to give better finish when facing...? As I found, the ends if the pot can go to the wipers of a pair of max/min setting pots to dial in the variation, too


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