To VFD or to not VFD

[matthewsx]

Hi and welcome.

If you're new and just want to get up and running ASAP I'd recommend a static or rotary phase converter. To get the most out of a VFD conversion you really need to rewire the machine, while it's possible to just run off a VFD at 60hz the phase converters are truly simple and cheap.

I'm running my 13x40 lathe off a static converter and it works fine. At some point in the future I may retrofit a VFD I don't feel the need for it yet. I do have one on my other lathe but it didn't have any electronics to start with so it's only the motor to worry about.

John

 

[BladesIIB]

I agree with everything said so far about going the VFD route. 6 months ago I did not even know what one was and now I have a PM 1440TL Lathe running on one and could not be happier. Thanks to mksj for all his help in teaching me the process. Below is a video of all of my learning that may help you get your head around a VFD and what you are re wiring on your machine to have it all work.

As for why?
Controlled start up speed
Controlled stopping speed
Fine tuning of speed during a cut to reduce chatter or speed up while facing for a better finish, or vary speed to get chips to break

Those are some benefits off the top of my head.

 

[G-ManBart]

Fine tuning of speed during a cut to reduce chatter or speed up while facing for a better finish, or vary speed to get chips to break.

His machine already has an infinitely variable speed drive (fairly rare on a SB), so he will have the ability to fine tune during a cut either way.

 

[BladesIIB]

His machine already has an infinitely variable speed drive (fairly rare on a SB), so he will have the ability to fine tune during a cut either way.

Fair enough. I was not familiar with the drive so did not know if you could adjust while running or not? Like with facing a large part I actually turn up the speed as it gets to the center to try and keep the actual cutting speed up while the diameter gets smaller. Will still get the controlled starting and stopping.

 

[.LMS.]

His machine already has an infinitely variable speed drive (fairly rare on a SB), so he will have the ability to fine tune during a cut either way.

G-Man - what you say is of course true. But using a potentiometer to adjust speed during an operation (while perhaps even using your other hand to move the compound) is far easier than trying to muscle a reeves drive.

 

[BGHansen]

I have two three-phase machines (Bridgeport 2HP and DoAll 16" band saw) both running on static phase converters. I've had no issues with the 1/3 reduction in horsepower, but I'm from the school "if I break it, I have to fix it" and run on the conservative side. The BP had the phase converter on it when I bought it. Worked fine so I went the same route on the DoAll. Really easy install on the saw, ran a 220V line to a DPDT push button switch mounted to the saw. The four wires from the saw dropped into a terminal block in the phase converter and it was up and running. The 3/4-1 1/2 hp phase converter was around $45 off eBay.

That being said, guys with vfd's love them for the added controls. Instant variable speed, braking, reversing, etc. They take more time for the initial set-up, but give you more features down the road if you need/want them.

The RPC puts the machine(s) in "as-designed" by the factory mode with no reduction in power like the static convertor. You'll see posts here with more pros than cons. Cons are the noise from the idler motor, more involved in the initial set-up, worry about leaving it running when leaving the shop, etc.

Both of my machines have Reeves-type variable speeds. Speed changes are a spin of the handwheel instead of a quick turn of a pot (VFD). It takes a little more time, but hasn't been enough of an inconvenience to me to switch over to a VFD (yet).

Bruce

 

[G-ManBart]

G-Man - what you say is of course true. But using a potentiometer to adjust speed during an operation (while perhaps even using your other hand to move the compound) is far easier than trying to muscle a reeves drive.

The setup South Bend used is actually quite different from most of the other similar systems. They put a hand wheel on the front of the machine, at waist height in line with the headstock, so it shouldn't be too hard to manipulate while doing something with your other hand unless the saddle was out there a ways. Not as easy as turning a knob, but not too bad.

 

[mksj]

If the reeves drive is working then one can go either route, in many cases the mechanical drives have failed and then a VFD with a larger motor is used. As others have noted the VFD allows controlled acceleration and deceleration and for a single machine is a bit less expensive than an RPC. They do take a bit more work/costs to install them properly and maintain safety. When using a VFD with a mechanical speed drive, I still recommend using the mechanical speed adjust for major changes, if left in one speed it will wear unevenly.