My compadre's new-er Kalamazoo horz'l band saw (I got the old one) is
dishing--ie, the mat'l in the vise, after a cut, has a low point in the
middle. On 3" diam alum, about .030; the bigger the diameter of the piece,
the more the dish.
What could be causing this? Aside from the dishing, the pieces are square,
the blade is tight (1", .030), he says the feed/speeds are right (proly
conservative), teeth count OK, plenty of coolant..
formerly Droll Troll
It has to be the actual hinge mechanism being worn, seems to me. If it were my
problem to diagnose, I'd start with a square piece and catch it in the vise so
the square end is just against the blade, then carefully and slowly raise and
lower the blade to see if the blade wanders without any load, saw turned off. If
it does, then for sure it's the hinge ears. If not, then it may be some strange
blade issue, and I think the second thing I'd do is to first carefully check the
guide adjustment and blade tension and see if that helped, and failing that I
think I'd try a new blade.
--I've learned that it's possible for a blade to be *too* tight. You
might want to ease off and see if it gets any easier. Also for aluminum
cutting, particularly thicker stuff, use *very* high speeds; i.e. similar to
what you have on a woodcutting bandsaw, with a blade of at the most 5 teeth
per inch; 4 is better.
I had a Kalamazoo, nice saws. Two things cause this kind of problem. The
first is the wrong blade tension. Too loose and the blade sags, too tight
and it stretches more at the back (soft area) than at the teeth (hard area).
Take the blade off and lay it on the ground, if it wants to curl up you had
it too tight. The second thing is weight on the blade. Too little weight
and the teeth rub instead of cutting, so you get poor blade life. Too much
and the blade twists to one side. One side of the teeth then do more work,
get dull and the problem gets much worse. Talk to the manufacturer about
the proper weight. By the way, just adjusting the hydraulic don feed valve
will NOT correct this problem. You either need to adjust a counterweight or
a counter balance spring.
Sawing with too fine a blade is also bad, especially on aluminum. Aluminum
cuts easily and the chip rolls up in the gullet between teeth. One the
teeth pack solid you get a slow crooked cut and the cut face looks smeared.
Teeth should be as coarse as possible, while always having at least two full
teeth in contact at all times. Too coarse and you risk breaking teeth off
or chattering badly. Most people err on the side of too fine, and would be
better off being a little too coarse.
Vari-pitch blades are wonderful. They allow cutting a broader range of
material thickness and greatly reduce chatter on hollow sections.
Hope this helps.
Gary H. Lucas