On Sat, 25 Sep 2004 11:22:07 -0700, in "Jafi" wrote:

Hello All,
I have recently rebuilt a 12" rock saw and I'm having trouble calibrating it
for a parallel cut. It seems that as the clamp travels it tends to move away
from the blade which causes the blade to bind.
I have measured and remeasured and still can't get it aligned. I have
realigned the blade shaft, I have realigned the clamp rails and I am getting
somewhat frustrated. It is the larger rocks that seem to have trouble
staying aligned. I don't put any rock larger than the clamp, (lengthwise)
and only about 3 - 4" high.
Is there a trick or can someone impart some of their experience and wisdom
on this newbie? Your help would be appreciated.
Thank you
Joe


Joe,

The classic way I was shown to do this is to clamp a pencil into the vise, adjust
it so it just barely kisses the side of the blade (with the blade rotating, and
then, also does the same when the vise is run down to the far side of the blade.
It can take a good deal of tweaking. The thing this accounts for is that blades
are rarely totally flat and true, so you're looking for the same extent of
marking on both sides, rather than a complete mark all around the blad. Get it
set so it scribes about the same length of arc on boths sides.

The other comment is to be sure the blade is mounted to the shaft as true as
possible. If there is any wobble in the edge as it turns, then there is the risk
that the blade will start into the rock slightly off it's true centerline, which
pulls the blade to the side as the cut progresses. that not only messes up the
cut, but can destroy the blade, by dishing it. So make sure the blade flanges
are really true, and the blade, truely flat, mounts equally true to the shaft.

which brings me to two other points. if you've trying to true up the saw with a
used blade, be sure the blade is not dished already, perhaps from attempting to
cut with a misaligned blade. A dished blade is good only for short trim cuts
unless you can get it flattened again (sometimes possible with careful
planishing...) As well, make sure the blade edge is uniformly sharp from one
side of the edge to the other. run the blade through a bit of fire brick or
dressing stone to be sure it's not glazed on one edge, which again, can happen
when the blade is not cutting true and is being pulled to one side. when that
happens, the blade tends to not want to cut in a straight line, but cuts faster
to one side, so even with a true blade and true vise, the cut can drift to the
side. Very early in my career (the start actually), I worked for a time for a
lapidary shop. the owner was in the habit of slabbing most stones by imbedding
them in concrete first. He'd started this with smaller hard to hold things,
putting them, carefully oriented,a nd perhaps held in position with a bit of
glue, into a milk carton, so he'd get lots of smaller rocks into the one carton.
then he'd fill it up with concrete. the resulting square block was easy to clamp
into the 24 inch slab saw, but equally, he'd found that the concrete was very
good for the keeping the blade properly dressed and sharp, so he sometimes did
the same thing with single larger rocks that he felt might tend to glaze the
blade, or where the shape of the rock offered a very angled surface that the
blade would have to start the cut into, with the concrete avoiding the
possibility of the angled surface deflecting the blade a little when the cut
started. It also reduces the chance of the slab breaking off just before the cut
completes, which often leaves a jagged end to the cut.

Hope that's of use.

Peter