Band saw blade keeps coming off

The blade

I feel an idiot for not being able to get this damned thing fixed myself, but I have a smallish bench mounted metal cutting bandsaw of good quality. OK, she's done a bit of work before I got her, but there's no wear in the bearings and the cast iron wheels run true. I have played with blade tension (tighter seems more reliable) and with the top (none powered wheel) tilt, which is adjustable, and the blade guide ball bearings, which are adjustable, but STILL the blade will suddenly jump off one of the wheels. 3 things look less than perfect. the wheels had some sort o gritty coating, when new, like coarse carborundum paper, this is now quite worn. The blade makes a noticeable jump as the welded part passes through the work piece. Nothing much, but when worked hard it is audible and can be felt. Finally the blade is quite old and not as sharp as it might be. Cutting alloy makes the blade come off more than steel.. Can anyone with experience of these machines point me in any directions to look to? Thanks!

Install new tires on the wheels.

Replace the blade.

Tom

Line up the wheels. Make sure they are in the same plane.

Crown the tires.

Install a blade with a good weld.

Back off the guides and adjust the wheel tracking so the blade tracks on the wheel crowns. Adjust the guides.

John Martin

Thanks for the replies, what do you mean by "crown the tires" please? The wheels are flat on the blade running surface and seem to have glued on abrasive coating, not something that looks to be (easily or cost effectively) renewable. Cheers.

First check blade weld and make sure it is straight. Next check the rubber tires. They should have a slight crown. If it has worn flat you need new tires. Sort of counter intuitive but the blade seeks the high spot as it is running. Next check the wheel alignment. Both wheels should be parallel and in the same plane. Lay a straight edge against both wheels. It should touch the top and bottom rim of both wheels. If not there should be a set screw or bolt next to the top wheel axel that adjust the angle and the powered wheel can be slipped in or out on its shaft.

The blade tension should be just tight enough that it makes a musical note when plucked and it is good practice to back off the tension when the saw is not being used.

The Bandsaw Book by Mark Duginski is primarily aimed at wood cutting bandsaws but the tuning chapter applies to both wood and metal.

Sounds like the tires have been removed. They are thin rubber bands that are glued to the wheels. They have a slight crown in the center. The crown forces the blade back to the center of the wheel when it gets off to one side.

It's a metal cutting bandsaw, they don't have rubber tires and the wheels don't need crowning. The blade needs replacing before anything else.

Tom

You sure about that, Tom?

John Martin

There's probably some political thing going on here, if one faction want's to believe in tires and crowning, who are you to burst the bubble and suggest the obvious?

What is the size of this bandsaw, is it two wheel or a smaller three wheel. Does fly off when cutting wood or metal, well it stay on when cutting wood but fly off when you try to cut metal?

Yes

Ya right, better retread the wheels, crown them, fit new bearings, guides, possibly rewind the motor and replace the switch. To actually suggest replacing a consumable before overhauling the machine was unthinkable. Thanks for the headsup Tom, I withdraw all previous suggestions as totally inappropriate. Hang on a minute, didn't I read somewhere, that you suggested replacing the blade?

Tom

You might want to write to DoAll and Grob and a few others, then, and tell them that they're wasting money by putting tires on their wheels. Oh, wait, those must be woodworking saws. Silly me.

It probably is the blade. But there are a lot of other things he should be checking.

John Martin

Except the saw in question is a vertical. A new blade is still the first thing to try.

Ned Simmons

What Tom said. The typical horizontal band saw has no crown, nor rubber tire. They typically have a shoulder, against which the back of the blade runs. If the wheels are properly aligned with one another, the blade will stay in place. A tired, old blade often will come off time and again. You can usually attribute the problem to minor dissimilar stretch of the blade. Try a new blade before anything else.

Harold

I was laughing so hard, my laptop hit the floor and I can't see through the tears.

Harold, SHUT UP they don't want to hear it! Except for poor Chris.