Bandsaw throws the blade

[Stern]

Have a typical HF type band saw (4 1/2") and been having a lot of problems today with it throwing the blade off the inside wheels. I have tried the "tilt" adjustment on the one wheel in all possible positions but makes no difference. Got to the point today I ti9ghtened the blade so much it snapped.
Any trick to these things ?

[sasquatch]

Gotta be an alignment problem, -adjusting these things can be pretty delicate at times, doesn't take much to get it it off track.

[Stern]

Figured as much, guess when I get a new blade I will have to expect to take a long time to get it tweaked just right.

[armedandsafe]

If you have replaced the tires, check that they are the proper thickness. I've found that most (all that I've used) tires are too thick for the HF saws and need to be dressed down after installation.

Pops

[CCWKen]

Does it throw the blade just running or when you try to cut something. Check the guides too. Sounds like it may be a worn/loose bearing causing poor alignment. Or you just plain don't have it adjusted.

[Bob Fisher]

FIRST, get a good quality blade! I have contemplated using a wrench to tighten my blades, as I sometimes have the same problem. If the blade runs OK when not cutting you may have a downforce issue. These 4X6 saws seem sensitive to too much force. And the spring counterbalance leaves a lot to be desired.Bob.

[valleyboy101]

I agree with CCWKen. If it is throwing the blade without cutting - loosen off the guides and see if it continues.
Michael

[darryl]

I looked at a new 4x6 bandsaw today- what a piece of junk! Sure glad I got mine before the slide-

Is the blade damaged? Best thing might be to put a new blade on it, then go through the procedures to get the tracking right. We went through this a month or so ago. A tracking problem that develops quickly is not likely to be a machine problem, IMO. Blades do deteriorate, not only in sharpness, but in the integrity of the backing. It's a waste of time trying to align the saw without a new blade on it, as all you'd be doing is trying your best to get a bad blade to stay on- with a proper alignment from the start, blade life will improve and so will the cutting action.

The upper and lower wheels should be in the same plane and parallel when the tension is on- not always easy to achieve, but measurable with a straightedge. You do need to know if the fault lies with the machine or the blade.

[outback]

There is a cure and a few causes for the blade jumping off the drive wheel.

Below is the cure. Screw a small plate to the saw frame to retain the saw blade:


The primary reason the blade jumps off the drive wheel is because the blade stalls or stops, the drive wheel continues to rotate and spins the blade off the drive wheel.

Below is the downside of my sawblade retaining block. When the saw blade stall/stops there needs to be slippage somewhere this is where:



In the 12 years I have owned and used this saw I virtually melted two fan belts and the belt guard is also a gonner. For this reason I do not run the saw unattended. I'm always nearby listening for the saw motor to run but no sawing taking placed.

Why does the blade stall or stop:

1) Took me a few years to figure this one out. If you are sawing rectangle stock and you fail to clean shavings off the support area it is possible the cut piece will be lifted just before the end of the cut. The cutoff piece will work just like a disk brake caliper and very efficiently pinches the blade and stopping it in it's tracks. The blade slips on the drive wheel and they part company.

2) Sawblade lacks enough tension to prevent slippage. I added a heavy duty die spring to the tension adjustment
so the idler wheel could float if it needed to.

3) The blade gets snagged in the saw kerf while sawing. Adjust down feed.

4) I have run this saw almost everday for 13 years and have yet to ever adjust the saw buides. I can't believe the saw still runs. I have a new saw in the shed, still in the unopened box as a backup saw. Been there 12 years.

Be sure to use bi-metal saw blades with about 18 teeth per inch. Fewer teeth may cause excessive loads on the saw and cause a stall.

May as well show you this. Notice the cut piece has no support at all and can never pinch the blade:



See the bar feed work


Jim

[dian]

http://bbs.homeshopmachinist.net/threads/58345-Adjusting-the-tracking-on-the-garden-variety-4x6-import-horizontal-band-saw?highlight=band

[sasquatch]

Outback that is a slick setup. (But i still don't understand why the need for the blade retainer block .)

[chevy3755]

what i did with mine was to remove the wheels and put them in the lathe and cut a deeper shoulder for the blade......worked great for me.....just my 2 cnts worth

[Stern]

Thanks for all the tips, it gives me something to look for. It runs fine and only throws a blade while cutting, so its probably a blade stall issue. I figure with all the cutting I have done lately (a LOT of big stuff) the blade probably got dull, as to even get it to cut I had to weigh the arm end down a bit (about a 1lb hunk of steel). Going to see how it goes with a new blade and thanks for the "teeth per inch" as the band saw has no info on it and not sure what blade I picked up (teeth seem really fine). Will grab a blade at Princess auto today (hopefully they have and I get the right ones, old one seems to be about 64"-65")

Thanks again for the help all, and I see if this gets me running again, then just need to find a way to determine when the blade is at a point it should be replaced (teeth did still feel sharp)

[Alistair Hosie]

If you have the max tightness on the blade and it slips might be the blade has stretched or maybe it was made slightly oversize in the first place I had this exact problem with a few blades I had the manufacturer made it about three quarters of an inch too long it's worth checking just my 2 cents. Alistair

[skunkworks]

We have a similar sized bandsaw that was bought in the 80's.. When we have had blade tracking issues - the bearings in the drive wheel gearbox failed. Sometimes the center race splits - some times the balls fail. we once had the shaft break (atleast twice). (this has been used hard for many years)

sam