On Thu, 7 Apr 2005 21:48:55 -0700, "Harold and Susan Vordos"
wrote:

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This is a problem that can have so many causes that it's almost beyond
the scope of a post.

First, how are you grinding? Are you subscribing to the notion that
you should constantly down feed your wheel and take large swaths with
each pass? You'll never achieve what I consider a good finish by that
method. You must learn to grind in a different manor.

Are you grinding dry? Heat alone will give you more problems than
you'll ever be able to overcome. If so, no matter what it takes, get
your grinder running with coolant unless you're grinding small items
like punches. Grinding creates an enormous amount of heat, which must
be dealt with. The expansion of the work makes holding a tight
tolerance almost impossible, to say nothing of the poor finish you're
likely to get regardless of your effort.

Are you grinding soft materials? Cold rolled steel, for example? Soft
material never grinds as well as hard material, but you can get a good
surface void of waves when things are right.

To change how you grind, I suggest the following:

Think of your grinding wheel as a milling cutter, which it really is.
It is a multiple toothed cutter that will cut very best by using a
corner. Try grinding your objects by picking up, then moving over to
the edge and feeding down a reasonable amount. If you have .010" to
remove, and it will come off one side, take .005" and run across your
item repetitively, feeding the cross slide roughly .030"/.050" each
pass, allowing the corner of the wheel to take all the meat off. Take
all your passes in this manner, with no down feed until you're ready
for the next pass. By grinding in this manner, the wheel takes all the
meat off with the corner, leaving the balance of the unaffected wheel
to constantly spark the surface. That yields the best finish, and is
actually much faster than grinding by the plunge method. It creates a
shoulder on the wheel that must be dressed off when it becomes a
problem. You'll know when, because the wheel doesn't cut well. It can
be because it's gradually developed a tapered shoulder, or it's
loaded. Loading is usually caused by the wrong density of bond or
wrong hardness of wheel.

The very best scenario when grinding is that you grind both faces,
whether they require it or not. That way you keep stress in balance,
so the part tends to remain flat. Try to take equal amounts off both
faces, even when it's not necessary. Your reward will be flatter
parts. Don't take it off one side then the other, take a cut, flip the
part, take a cut, flip the part, etc., until you're to finished size.
That's the best way to achieve a good finish and a flat part. Your
final pass should be something like .0005", with a freshly dressed
wheel.

If you have a manual grinder, you're not nearly as likely to be happy
with this process as you might be if you have a hydraulic feed
machine. Unless you're involved in fine toolroom grinding, I highly
recommend you avoid manual machines. I've done some very difficult
toolroom grinding with several hydraulic machines, but can't imagine
grinding large surfaces with a manual one. You can turn on the
hydraulic machine and grind as I recommend while you're doing other
tasks.

Be certain that you have matched the wheel to the work at hand.
Aluminum oxide wheels for steel, always. Never silicon carbide. Using
a silicon carbide wheel on steel creates a glazed wheel almost
instantly, and that generally leaves a wavy surface. Too hard of a
wheel does the same thing, and a too soft wheel breaks down so fast it
almost always leaves a rough finish.

Wheels that are properly selected will cut without loading and leave a
decent finish, assuming your grinder has not had the motor replaced by
another motor (that has not been precision balanced), and has good
spindle bearings. Even a V belt can cause your finish to suffer. It
must run smoothly and not transmit any type of motion to the spindle.
The slightest vibration will translate into a poor finish. As little
as a few hundred thousandths variation show up as waves in your
finish. Use a hard wheel for soft material, and a soft wheel for hard
material. Wheels must break down at a proper rate (to stay sharp) in
order to achieve a good finish.

Are you running your grinder single phase? You're likely to never get
a good finish if you are. The uneven power pulses tend to translate
into the finish.

If you can provide more information I may be able to provide some
guidelines.

Harold

Excellent post Harold

gunner

Rule #35
"That which does not kill you,
has made a huge tactical error"