I just bought a Boyer Schultz surface grinder 1 horsepower 208/220
volt 3400 rpms for my home shop and I cannot get it to run with my 1-3
horsepower static phase converter. It runs perfectly where I bought it
on their 3 phase wiring. My converter runs my 1 1/2 Bridgeport and 3
horse lathe fine. I've triple checked my wiring and its right. Could
it be the higher rpms of this motor? Has anyone else run across this
Thanks for any help or thoughts.
Try starting the grinder while the lathe motor is running.
Some motors are just not happy running with a static
converter. The grinder will also not run as smoothly on the
static converter, which really only gets the motor spinning
so it'll run on single phase.
I see a VFD or rotary converter in your future...
The so-called "static" phase converter is simply a capacitor to
shift the phase of power applied to one of the three wires while the
other two get the standard 220 single-phase. They are made to work with
a particular range of motor horsepower, and probably are sensitive to
the number of poles in the motor. A 3400 RPM motor is a two-pole (and
without slip would be running at 3600 RPM). A four-pole (more common)
is at some slip-determined speed below 1800 RPM (1700 or 1750), a six
pole is some slip-determined speed below 1200 RPM and so on.
You may need a higher value of capacitor for a two-pole motor.
Or perhaps a lower value.
But in any case, once the motor spins up to speed, the shifted
power to the third phase will be automatically removed, and you will
lose the benefits of three-phase power to the motor (which include full
horsepower, and smoothing out of torque pulsations which can show up in
the grinding finish.
Your choices for a good finish are:
1) Use the "static" phase converter to start an idler motor (some
used three-phase motor of about 50% or better more horsepower
than the load to be run), and add tuning capacitors to it to
balance it for smooth and even power output. Don't worry if the
output shaft has been damaged by a slipping pulley or by the
process of removing the pulley. You don't need it at all, and
can even machine it off if you so desire. (If you don't machine
it off, put some kind of shield over it, so nobody can come in
contact with it, for safety.)
2) Get a VFD (Variable Frequency Drive). And electronics box which
takes in single phase (or three phase) and synthesizes three
phase to drive whatever load. One benefit from this is that you
can use it to vary the speed of the motor, by varying the
frequency of the applied power. I don't think that this feature
would be a benefit on the surface grinder, though it would be
nice to have on the mill (or lathe). It will let you put a knob
(potentiometer) within easy reach to change the speed smoothly
while it is running. If the Mill (or lathe) has a step pulley,
this will let you tune the speed more finely than you otherwise
could. If the machine has variable speed, you can do without
it, but it is nice to be able to have a knob right by the
carriage on a lathe so you can vary the speed as you face off a
large workpiece, so you can avoid that band of poor finish
somewhere between center and OD where the speed is just wrong
for the combination of workpiece material and tool material.
Note that, as someone else already suggested, you can use the
existing Bridgeport spindle motor as an emergency idler motor while you
are starting the surface grinder -- and probably get better finish than
you would if the "static" phase converter were to actually work with the
surface grinder's motor.
Note, also, that at some serious risk to you hand, it is
possible to spin the wheel by hand just before switching on power and it
will likely spin up, even without the phase converter. Be careful that
you spin it in the right direction, or when you start to grind you may
wind up unscrewing the nut retaining the wheel, which can make things
rather exciting. :-)
For running multiple machines, I would suggest the rotary
converter route, with someday adding a VFD to the machines which can most
benefit form it. A home-built rotary converter can be very inexpensive,
and once the idler is spinning, it is not really sensitive to the load
motor horsepower, as long as the idler motor is large enough.
P.S. I wish that my little Sanford surface grinder had a three-phase
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Interesting to note, we recently had our local metalworking club meeting
and we built a rotary phase converter. The first motor, an older 1725rpm
motor was to be the idler, kind of groaned and spun slowly if at all. We
added another electrolytic capacitor and that helped but still made a
racket and spun slowly. We were at a shop with 3 phase power. We checked
it and the motor ran fine. We had a 5hp 3450 rpm motor and moved the
converter over to it. Fire it right up. We noticed the number of wires
coming out of both. We could only surmise that the little 2hp motor must
have been Delta wound instead of star wound.
Perhaps you can look at the tap chart on your Boyer-Schultz motor and
tell us exactly how it reads. I bet you have the same problem.
As someone suggested, if you can parallel your lathe or mill to your
grinder, fire up the mill first then the grinder, let us know if it
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