Grinding lathe jaws with Die Grinder/ What Abrasive to Use?

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
Reply to
Steve
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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
Steve wrote:
-- _-_- BEAR Labs - Custom Audio Equipment, Cables, Mods, Repairs -
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Reply to
BEAR
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" shank.
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.
My 2¢
Orrin
Reply to
Orrin Iseminger
"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. Good luck, Tom
Reply to
Tom Wait
snip
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 near zero!
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 dimensional errors.
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!
Jim
Reply to
pentagrid

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