On 12 Dec 2004 18:29:33 GMT, (JMartin957) wrote:

One of the claims made about the VFDs was that the current they supply is not
true 3 phase, but has some harmonics or secondary oscillations which can cause
problems with some older motors. This seems to be rare, but might be your
problem.

This is indeed quite true. Until I got my 5hp rotary..I was running
all my (then, very few) machines on a single 5hp VFD. Oddly enough the
old Clausing 6525 would leave a slight herringbone pattern on one
direct drive speed setting. I had assumed it was something worn in the
headstock. When I went to the RPC..the pattern vanished. I then
swapped back and forth and indeed, it was the VFD. None of the other
machines exhibited this phenom, including the surface grinder, which
gives the same finish either way.

A cautionary note...if you were to power up your surface grinder via
vfd,..be damned sure..that you set the maximum rpm rating to less than
that of the max rpms of wheels. IRRC 3600 rpm. It would be very
possible to over spin a wheel and have it catastrophicly disassemble
itself..which will result in a grenade going off on your grinder.

Gunner

"To be civilized is to restrain the ability to commit mayhem.
To be incapable of committing mayhem is not the mark of the civilized,
merely the domesticated." - Trefor Thomas