Balancing a 7" grinding cup wheel

[Greg Carter <greg@zzzzzzzzzzzzzzzzzzzzzz>]

I mentioned in my last post that the 7" grinding wheel was vibrating a
lot.  I figured it was the cheap $35 grinder.  So I purchased a good
name-brand variable speed 7" grinder and I had the exact same horrid
vibration.  Doh! The whole assembly would vibrate excessively.  To the
point that the cheap grinder started to fall apart, the locking
mechanism fell out.

So it had to be the wheel.  When I bought the wheel I figured I'd get a
good one and paid over $100 for it.  I'd only used it for a few hours.
Maybe I should have just sent it back but I figured I'd try to balance
it myself.  This is the first 7" grinding cup that I have ever owned.
So I'm not sure if this is a common problem or not.  It did not vibrate
bad when it was first new.  Only after some use.  All the segments
showed the same amount of wear and I don't believe the vibration was
caused by misuse.  Anyway, here are some pictures of how I balanced it
in case anyone else experiences the same problem.

I first cleaned the wheel of any hardened slurry then centered it on a
piece of 5/8" threaded rod, which is the same thread on the grinding
wheel and will be for anyone else in North America.  Then set up two
pieces of angle iron ( parallel ) so that the threaded rod can roll
along the angle iron.  It's important to get the rods level to each
other and level along their length.

http://tinyurl.com/kkt24

Then you start the wheel to roll.  Do it a few times, it should always
stop with the same point pointing down.  That is the heaviest end.  If
you turn it 90 degrees either way it will drop back to the same
location.  Here I've marked the heaviest end.

http://tinyurl.com/ewsna

Then I started taping on bits of scrap metal until I found a size that
would roughly counter the heavy end, adding it 180 degrees opposite.
The next two pictures show that with the counter weight added, the wheel
can now be placed in any position and remain stationary.

http://tinyurl.com/j96lk
http://tinyurl.com/j5z9o

Then I ground off a little more from the scrap piece of metal to account
for the weight of the weld.  I used a MIG welder and tacked it on.

http://tinyurl.com/lhwy4

Now it spins nice and smooth. At least when it is free-wheeling.  When
grinding it hops around a bit but I figure that is just the nature of
the 7" cup wheel.  It is at least controllable now.  Of course it may
not be worth your effort to bother balancing the wheel, and just buy
another one.

The method I used to balance the wheel came from this article from 1901
http://www.lostcrafts.com/Blacksmith-71.html

In case tinyurl stops working, original url for the pictures is here
http://www.carter-engineering.com/images/grindingcup/

bye.
Greg.