"Harold and Susan Vordos" wrote in
:

Wow! Very impressive looking machine, and a total surprise. The one
I'd seen had horizontal spindles with a carrier for the part which
oscillated back and forth between the two wheels. Very old
technology, to be sure. One of the jobs the shop was running with is
was the slide portion of a pistol.

This machine is the smallest one they make. But you know how it is, the
smaller the part the smaller the tolerance. It's tough to see in the
photo but the fixtures are actually gears. So the parts rotate from the
inside of the wheel to the outside while rotating around the wheel.
eventually during the cycle all of the workpiece surface gets ground by
every bit of the wheel surface. The flatness and parallelism are really a
function of the bearings in the machine, and the machines ability to
resist deflection. The feedrate is determind by pressure, same as flat
lapping. The machine has auto sizing via an in process gage which is made
by Sony.


I'm not familiar in the least with CBN wheels, considering they were
not in use when I retired from (commercial) machining. I gather that
such a wheel is more or less a necessity for the work at hand, but I'd
be inclined to use a different wheel, assuming that would be possible.
You didn't mention the material being ground.

The one job we had trouble with we were single side grinding. The
material is 52100 low 60's Hrc. I can't remember exactly and don't have
the drawing here at home. CBN is the only way to do this type of
grinding.


Funny, talking about .000060" and having it be a concern. Yeah, it
doesn't sound like much to worry about, but when you have no tolerance
to speak of, it obviously spells the difference. I think it's hard
for the average machinist to grasp the concept of fine work. So much
so that I've commented more than once that it takes a special kind of
guy to be successful in the grinding department. Some guys never
really make the grade, yet may have years of shop experience.

To tell you the truth it's surprisingly easy to achieve these tolerances
on this machine. (When the wheel doesn't fall apart) One of the other
parts we did double disk grinding, we ran for 24 hours and had a total
thickness deviation of 1.6 microns and flatness and parallelism never
exceeded 1 micron. I'm willing to bet that if we re-cleaned and rechecked
the parts that were at the extremes we would find that the deviation was
smaller.


About the chipping. I can't help but wonder if it's not being caused
by your parts chattering slightly.

That's our current thought. The parts that the customer has supplied have
way too much variation, so the tall ones are under pressure and the short
ones might be jumping around as they pass beyond the edge of the wheel.
Either that or we have a bad wheel.

Your operation being a total
stranger to me, could it be that your coolant plays into the problem?

You might not be familiar with what we are doing but you're thinking is
dead on. The wheel manufacurer was certain it was the coolant. We were
using an equivelant to the one they sell. We then switched to their own
brand and the wheel still chips. They were claiming that the damage was
already done by the coolant we were using. Then I pointed out that the
lower wheel didn't chip and its flooded in the coolant. Hmmmm. Well then
you must have crashed the wheel. I'm telling you, that never happened. If
it did I would just get another wheel and get on with my life.

For typical grinding, the level of concentration of lubricant (in the
coolant) isn't critical, more for rust prevention than anything, but
when you use machines that rely on surfaces for support (like when
grinding on one side only) it could be you need more lubrication. We
always ran a higher level of concentration in the centerless grinder
for that very reason. It's interesting that it happens when grinding
single sided, which prompts my chatter question. My other suggestion
would be feed rate, but without understanding how the machine
operates, I'm not sure I'd be in the ball park.

Like I said the feed rate is controlled by pressure. We are starting out
at low pressure until we get to a point where we are certain that the
wheel is contacting all of the work. Then it shifts to a higher pressure
and then back to low as it finishes. The lubricity idea is interesting.
I'm going to look into that some more. When we are single side grinding
we are using hardened fixtures that ride on a hardened plate. The part we
are grinding locates on a shoulder in the fixture. So there is
opportunity for something to stick. The speeds are fairly slow though and
the flood of coolant is immense. I am thinking that we could re make the
fixture so that the workpiece doesn't come out from under the wheel as
the fixture rotates around. The problem then becomes we would have to
desin a dummy part for the in process gage. (this part is very small) The
double disk ground workpieces use a dummy part mounted on the periphery
of each fixture for gaging. These dummy parts are larger in diameter than
the part being ground.


I looked at the lathes offered by your firm. Sure makes me breath
easier to know that if I was really in need that there are still
reasonable machines on the market. I was particularly impressed by
the one model that offered 2,500 RPM at the spindle. I'm running a
Sag 12 Graziano that I bought new in '67, and I"m hoping it will see
me through to my dying days, but I'd not hesitate to buy something
similar (new) if the need arose. I'd rather it didn't come from
Harbor Freight, if you get my drift!

Thanks. I don't have anything to do with the "manual" side of the
business, but I can get knee mills and lathes at a discount for you if
you ever need one. The Harrison lathes are good quality of course, but I
have been pleasantly surprised at the 14x40 Nardini that we have at our
office. We have a small tool room and the home office let me have a new
Nardini. I would have loved a Harrison Alpha but for what we do the $$
don't make sense. The Nardini is a better machine than I expected,
cetainly better than most although not quite as good as the Harrison
manuals. I just can't get used to the "lay-out" of the thing. Small
complaint I guess.

Anyway thanks for bouncing this around with me. I've got a couple more
ideas as a result.




--

Dan