bandsaw blade slipping off pulley?

[mikem]

My Wilton H/V bandsaw works well most of the time, but the blade slips off the bottom pulley when the blade gets stuck in something. It looks like one of the cheap 4 x 6 Harbor Freight saws only it has a little more capacity. Last night I was sawing some .125 HR steel plate and the blade slipped off about 6 or 7 times--what a pain! Is tension of the blade a factor? Is there some alignment of the lower wheel possible?

[J Harp]

Yes the blade tension is important, on the 4x6 it needs to be about as tight as you can get it by hand. Also important is the alignment of the wheels, they must be in the same plane. Put a straight edge against the drive wheel so it touches top and bottom of the wheel, and check how closely the top wheel lines up with the straight edge. If the top wheel is forward or back of the drive wheel then it needs to be moved to bring it in line. I don't know how yours adjusts, but mine had washers behind the upper wheel, I removed them but still not enough to get it in line, had to do some surgery on the top axle. That fixed the jumping off problem for me. Your problem may be different, but keep studying it and you'll mostly find what needs to be done.

[BadDog]

Absolutely. When I've seen this on my HF 4x6 it was one of 2 things. Either I didn't have it tight enough, or I was using cheap HF blades. Lynox blades fixed that latter. :D However, if you did not set the initial tracking correct (on the outboard wheel) you might get this problem too. Does the blade ride full against the back wall on both wheels?

[Alistair Hosie]

serious point make sure the blades are not too large even by a few mm for the size of bandsaw you have this happens all the time.Alistair

[mikem]

Hi Alistair--I'm sure that the length is about right--when it slips, it is hard to get back on without loosening the handwheel so much that it falls out of the nut that tightens the idler wheel. Are you thinking the blade is too long or too wide?

Bad dog-- I am using a black bulk-made blade that I got from the welding supply place--maybe that is part of the problem.

I will tighten up the blade some more and see what that does.

Thanks to all-- and Happy New Year!

[Mike Burdick]

Just curious...

Was this problem present when you bought the bandsaw or is this something that has just started recently?

[mikem]

It has slipped before but it has happened more often lately. The blade has been changed and the tension is not as high as it maybe should be. The previous blade was a satin finish gray steel color and my new one is more shiny and darker color, almost black.

[Mike Burdick]

Mikem,

Okay...since the problem is getting worse, perhaps this may apply to your bandsaw as well.

I had a wood cutting bandsaw that would throw the blade when it was stuck or became slowed. The bearing on one of the wheels was worn just enough such that the "extra" torque caused by the "stuck" blade forced the wheel to run a bit off plane. Zip...off came the blade!

I'm not too sure if it was the bearing or the bearing fit but when it was replaced, my problem was solved. Have you checked the bearing or the bearing fit into the wheel?

[Tim Clarke]

OK, I'll jump in here and ask do you have trouble when sawing in the horizontal mode [material secured in the vise] or vertical, with the head raised and the removeable table installed? I had trouble when freehand sawing plate in the vertical mode. When I tried cutting too small of a radius, I had blades jump the wheel, or even break. I thought at the time that I had the tracking and tension as good as I could get it. When I started ordering premium blades from Enco [Starrett and Kennemetal] my problems went away. Now I get a year out of a blade. The only thing I do different is to use a coarse tooth blade for thick aluminum, I think it's about 6 t.p.i. The variable tooth blades I use most of the time for general purpose work don't seem to clear the swarf very well on aluminum over about 3/4" or so.

Based on my experience, the more expensive the band, the cheaper it is, long term. Those who saw for a living have doubtless a brand specific recommendation, based on testing that I will never be able to do. However, I'm sure they will agree brand X blades are seldom a bargain.

An interesting thought would be to weigh the amount of swarf one blade would make before death.

[DancingBear]

Were you by chance using a coarse blade to cut a thin section? I've had blades jump under such conditions. I eventually learned that you should always use a blade fine enough to have 3 teeth engaged in the work at all times. That should help keep the blade from getting stuck.

I have to agree with Tim, quality really counts with bandsaw blades.

Walt

[Ken_Shea]

Had a similar problem where I had to remove the pulley and re-machine it flat. It had worn a very slight taper to it over time, apparently it does not take much as it has been fine since.


Ken

[mikem]

My blade is a 14 tooth and I was cutting .125 steel HR plate in the vertical position. Three teeth in the cut would mean using a 24 toothed blade. Isnt that so fine that it would burn up (read dull) easily? Do they even make 24 tpi blades?

[sidegrinder]

I'm with DancingBear on this one. I normally run Lennox 10 tooth blades for everything. This is problematic on stock thinner than .250" or so. The teeth snag and then the whole blade jumps. Increase your tension a bit and then test it on .5" or so vs. .125". If it still jumps on the thinner stock but not the heavier, you need a finer blade. Or just use a hacksaw on the thinner stuff like I do ;) Sidegrinder

[DancingBear]

My blade is a 14 tooth and I was cutting .125 steel HR plate in the vertical position. Three teeth in the cut would mean using a 24 toothed blade. Isnt that so fine that it would burn up (read dull) easily? Do they even make 24 tpi blades?

Yes, they do make 24 TPI blades, I did a search at MSC and found a bunch.

As long as you keep the feed rate reasonable the blade should do OK, I usually use a coarser blade but keep a 24 TPI around for just this sort of job. I'm still on my first one, granted I don't use it that much but it's definitely had a few hours on it and it's still cutting well.

Walt