On Fri, 10 Feb 2017 02:26:07 -0500, micky
wrote:

In sci.electronics.repair, on Fri, 03 Feb 2017 10:01:43 -0800,
wrote:

Hey All,
I have an old Baldor bench grinder. Probably 70 years old or older.
The motor is the type that uses a capacitor for starting and running.
There is no centrifugal starting switch. I know this type of phase
making scheme provides lower torque for starting so that the motor
takes longer to come up to speed. But this grinder takes 5 seconds to
reach operating speed, 3400 rpm. I replaced the bearings in the motor
and it now spins very easily. There is a 3/4 wide 6 inch grinding
wheel on one side and a light weight 6 inch diamond wheel on the other

This sounds so cool. I want one.

I found this at a modest price, $17, but maybe I'm blind but I can't
figure out the diameter of the wheel, the diameter of the hole, or even
the width of the disk. I'll bet the thickness of the disk is under a
quarter inch, and that the hole is either standard or I should have an
adapter, but what is the diamter of the wheel? (I have to go to the
basement to remind myself what I use. 6"?)

BTW, what do you use it for?

side. The cap in the thing might be the original cap. It is a large
round tinned metal can with solder lugs. 330 volts and 400mfd. Could
it be that it needs a new cap? I don't know what kind of cap it is.
Oil filled I imagine but from the high mfd campared to all my other
run caps could it be an electrolytic cap? There is no sign of leaking

They can fail without leaking. The one in my Hallicrafters failed after
60 years or so, which is a long time but it still failed. I coudln't
easily find a replacement so I replaced it with 10 smaller ones of a
different sor in parallel, but this was a power supply filter. I don't
think that kind of substittuiion works for starting a motor.

and there are two places on the top of the cap where it looks like
holes were sealed with solder.

Hmm. I don't think that's anything.

You can test a big cap like that with an analog meter. Unsolder one of
the wires, and put the meter on ohms across the two connectors. If it's
good, the needle will go far to the right and then go gradually to the
left. Then reverse the test leads and it will do the same again.

Thanks,
Eric
The grinder is for sharpening tungsten electrodes for TIG welding.
When I got the grinder it needed new bearings so I replaced them.The
wheel guards are cast with the end bells of the motor. The right side
guard had been hacked up by a previous owner which was fine with me
because I wanted the diamond wheel to be completely exposed so the
grinding can be done on the top of the wheel. To that end I machined
the rest of the wheel guard completely away. The electrode is held
basically horizontal when presented to the wheel and then either
tilted slightly and/or moved past the vertical wheel centerline to
get the desired angle on the electrode. The wheel on the left side of
the grinder needs a guard because it is a typical grinding wheel. This
wheel is used to remove any contaminating metal on the electrode prior
to the diamond wheel use. I trued both wheels but there was still
significant vibration so I replaced the large old out of balance wheel
retaining nuts with new small nuts. Now the grinder runs very smooth.
One advantage of this capacitor run motor is the low vibration because
it is always operating as a two phase motor, though imperfectly.
Because the cap is always in circuit and the two windings in the motor
identical the cap is a compromise between a starting cap and a running
cap. The grinder is very well made, but that's no surprise because it
is a Baldor grinder and Baldor made and still makes very good
grinders.
Eric