"Joseph Gwinn" wrote in message
...
I recently acquired a bandsaw that will cut wood or metal (aluminium at
3000 fpm and steel at ~100 fpm). It always cut at an angle with the
original cheapo blade. Tightened and adjusted. No dice. Gave it a 5/8
inch wide 10-12 tpi bimetal blade. Much better, but still crooked.
The bandsaw books in effect say that this is to be expected, and
describe various ways to cope with the tendency, but I could not see why.
The mitre guage that came with the saw is pretty flimsy, but even that
didn't seem to explain the degree of crookedness. Now, on table saws,
the greatest accuracy is obtained by use of a sled that carries the
stock past the blade.
So, I made a sled out of a 3/8 by 3/4 by 12 inch cold rolled mild steel
bar (that slides in the mitre slot in the table), a piece of 1/4 inch
6061 T6 aluminium plate about 6x8 inches that I had laying around, and a
piece of 3/8 by 3/4 inch aluminium bar (set vertical and accurately
perpendicular to the steel bar and thus mitre slot). The pieces are
held together with some large flat head socket cap screws. The sled
reaches to within 1/16th inch of the blade, so the stock is well
supported.
In use, the stock is held in the sled against the aluminium bar, and the
sled is pushed past the blade. On wood, this works quite well, but on
metal it still drifts a bit, the stock being held in the sled by hand.
So I drilled another hole in the sled to accept a 1/4-20 flathead socket
cap screw, and attached a small strap clamp. This allows the metal to
be clamped firmly to the sled. This works: the cuts are now
perpendicular.
So, the lesson seems to be that a significant cause of crooked cuts is
the stock drifting sideways while being cut. I don't know the source of
the sideways force, but it cannot be that large. It may be nothing more
than the vibration of the saw causing imperceptible walking.
Joe Gwinn
5 band saws here, mix of BIG wood and H+V metal, and never a blade goes on
without the stretch gauge getting clamped to the blade. The blades need to
be re-tensioned often. We fought long and hard with bandsaw blades...DON'T
GET MOORES BLADES!!!!!!!!!! THEIR QUALITY IS INCONSISTENT, not always bad
just never the same. Get the stretch specs from the mfgr., not from a
table. We also use aftermarket ball bearing guides that are set-up
perfectly...big difference!
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