"Chuck Sherwood" wrote in message
...
3/4 hp 3 ph. motor looks original. Maybe this coupling is effecting
the finish?


Lots of factors to consider.
- grit and hardness of the grinding wheel.
- how you dress the wheel
- are you using coolent?
- are you using VFD, static phase converter, RPC ??
- feed rate
- hardness of material
I'm sure harold will have a few more!

You're right. Lots of factors, most of which are not real obvious and may
not appear to be related. My money says the machine has bad bearings, but
it could be something else. I'll toss in some ideas, but without seeing
the machine, it's really hard to get a clue.

Most importantly would be matching the abrasive to the material. Aluminum
oxide for steel, never silicon carbide, be it green or black. The wrong
wheel will yield that result almost instantly due to it's behaving as if
it's dull or loaded.

Wheel should be firmly tightened, but not over tightened. Use short handled
tools with no cheaters.

It is well known that minor bearing defects in surface grinders will
manifest themselves as waviness---and it takes less than .000010" deviation
for the surface to appear that way. In essence, if the bearings are
marginal, it's not beyond reason for the surface to have a wavy appearance,
all the while being quite flat, at least in general shop terms. Nothing but
bearing replacement will fix the problem, and then only if the bearings are
installed properly, and they're high precision bearings.

A wheel that is too hard will also yield similar results, as will a loaded
wheel. Each of those conditions are very similar to one another and are
often hard to discern from one another. A close inspection of the wheel
will often speak volumes.

It's entirely possible the coupling is affecting the finish, particularly if
it does any moving about. Flat surfaces are very sensitive to minor
deviations, and it takes very little to create an undesirable pattern. If
the machine was belt driven, I'd even suggest flutter in the belt, which
often has a profound affect on the finish. Any similar action by a coupler
could be a problem.

Grind wet, if possible. Dry grinding is always trouble, and should be
avoided if possible. Flood cooling is best, but spray mist is better than
nothing.

I suspect the shims are heat treated, maybe around 45/50 Rc. An aluminum
oxide wheel, maybe a Norton 38A, 46 to 60 grit, L or M hardness, vitrified
bond, diamond dressed (don't break the corners as Grant suggested. That
serves NO useful purpose), and *don't* plunge grind. Start on an edge and
feed across, maybe .030" per pass, with anywhere from a couple tenths up to
maybe .005" depth of cut (how they stay put on the chuck will determine how
much each pass will tolerate, plus how much has to come off will also
dictate), and allow the balance of the wheel to spark the part. Grind all
the way across the part (@ .030"/per pass), until the wheel leaves the far
side. If finish is important, dress the wheel and take a finish pass of
only a couple tenths, again, about .030" per pass.

As you suggested, block the pieces with a thin steel strip to prevent them
from moving under the wheel. Grind this way until the working edge of the
wheel starts to break down such that finish starts to suffer, at which time
you should dress the wheel slightly more than the depth of cut, to restore
the wheel to a flat condition side to side. You should be able to grind
one hell of a lot of pieces before the wheel needs to be dressed. If not,
there's something wrong with your choice of wheel. Remember, softer wheel
for harder material, harder wheel for softer material. Finer wheel for
better finish, coarser wheel for faster stock removal, but at the cost of a
better finish.

Harold