RE: [CAD_CAM_EDM_DRO] Re: VFD for series 1 bridgeport

> -----Original Message-----
>
> Any recommendations for a good, cheap VFD? I didn't know they
> convert to single phase. Cool! I do have a rotary phase converter
> but will be purchasing a VFD soon.

Go to http://www.dealerselectric.com and check out the inverter drives
(VFD). I have not tie to them other than being a satisfied customer. You
will need to derate the unit by 50% to use it as a phase converter so for a
2 hp mill you will want a 5 hp VFD. I don't know if they have any left, but
the used 7.5 hp Motortronics 230 v units they have listed at $350 are really
nice. Got one from them a few weeks ago for $305 plus shipping.

> If I'm understanding you correctly, Tim, the air motor stops and
> starts on command, and thus the RPM only changes while the shaft of
> the air motor is turning. So, could I put in a hand crank there and
> leave the machine at a high RPM setting using the VFD to control
> RPM? Then, whenever I need additional torque I could crank it down
> but would still use the VFD to control RPM....????

Yes, if your speed change works anything like the one I have and have seen
then the air motor was just an automated way to do what you can with a hand
crank. So you can make most of your speed changes from the VFD and only use
the built in speed changer to make when you need to radically vary the RPM
or if you need to use the back gears.

> Will the VFD brake the spindle motor also?

I have 2 different Motortronic VFDs now. One has built in brake resistors
and will very rapidly brake the spindle. The other has some breaking effect
(20%) and if you want full braking you have to add an optional resistor
pack.

Tim
[Denver, CO]

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