I need to grind the jaws of my worn out 3 jaw Buck Chuck. I have tried
everything else to fix it and nothing worked. I am going to use a
Milwaukee Die Grinder mounted in a jig in my tool post to grind the
jaws. My question is what type of abrasive stone should I use to grind
the jaws? Thanks, Steve
There are some detailed posts and references to this issue in the past -
try a google search on the newsgroup to find them?
I'd suggest (seat of the pants) very light cuts with a relatively fine grit...
iirc you want to spin the chuck while making the very light cuts
I presume you know the various methods to set up the jaws before the cut?
And that if the problem is in the scroll or the scroll's centering that the cut
will only work properly *at the exact diameter* that you make it? Of course
it still might be better than before... Also the larger the diameter
of the stone, the better, since you'll get closer to a flat cut.
I've taken to aluminum foil shims on my beater 3 jaw chuck... real soon
I need to buy a new 4 jaw chuck and forget about ever having this problem
again. :- )
Donations of small 4 jaw chucks will be gratefully accepted...
_-_- BEAR Labs
- Custom Audio Equipment, Cables, Mods, Repairs -
I've ground the jaws on a couple of chucks and never paid much
attention to the stone. IIRC, I used a Dremel stone mounted on a 1/8"
There is a much bigger concern than which stone to use. Jaw preload
has to be equal. If it's not, you'll wind up in worse shape than you
were to begin with.
You're probably aware of the cloverleaf-shaped preload fixture, cut
from a piece of steel plate. I discovered that this plate has to be
accurately made. If not, the jaws will get unequal preload. I tried
laying out the holes with a divider and center-punching the hole
location. Big mistake. That's not accurate enough.
In the long haul I was able to remove the bell-mouth from the jaws and
get the runout down to an acceptable amount, but it took a long time.
If you value your time, any, you might want to consider replacing that
chuck with an affordable Bison.
"Orrin Iseminger" >
The preload should be in the closing direction if that's the way you use
your chuck. Make a plate that is 'Y' shaped with the legs 120 degrees apart.
A circle scribed around the 'Y' should be somewhat larger than the center
bore of the chuck. Clamp the chuck on it using the teeth of the jaws that
engage the scroll. That way the whole surface of the jaw can be ground front
to back as there will be clearance behind the gripping surface of the jaws.
The Y does not have to be toolroom quality. A drill and a hacksaw will get
the job done as it is self centering.
This is a fundamental failing of the frequently recommended clover
leaf preload fixture. This fixture interposes solid blocks of metal
between each of the three gaps between the jaw faces. Unless each of
the three lumps of metal AND the jaw face dimension are EXACTLY equal
the jaws will tighten hard on the single jaw pair gripping the largest
dimension - the load on the remaining jaw pairs will be an unknown
lesser value. An error of less than 0.001" may well reduce the load to
The cure is spring load the jaw face force by adding a radial
sawcut in the centre of each of these blocks. As the chuck jaws are
the tightened the spring rate of these sawcuts ensures near equal
loading on each of the jaw face pairs and much less affected by minor
A sidelight on this is a the pretty undesirable practice of
gripping rectangular stock in a three jaw chuck simply by gripping
opposite faces between two of the jaws with the third face pushed
against the third jaw. I can't imagine any chuck manufacturer
recommending this but there are times when it is very convenient!