Why are my bandsaw blades breaking?

[dennis thompson]

I have a 10" Craftsman bandsaw which has served me well for at least 10 years. All of a sudden I'm breaking blades, 3 in the last month. The blades are not breaking at the welds. I'm using the bandsaw mostly to make small parts for toys . The tires are original, could that be the problem?, even if it isn't, given that they are 10 years old, should I replace them anyway?
Any thoughts/suggestion would be appreciated (although recommendations to buy a new bandsaw are not what I'm looking for?)
Thanks

[lowell holmes]

My tires were jumping off the wheels on my 14" Jet. I bought new neoprene tires and put on it/
This was at least 5 years ago.
I had to warm the tires by heating them in the microwave in order to stretch them while putting them on.

[Roy Petersen]

I'd suggest the tires aren't to blame, as long as the blades still track properly. I had only recently retired a 12" Craftsman that I'd had since it was bought in the 80's, also for toy making. When I was finding my blades were breaking it was generally forcing a dull blade to work harder, or bad thrust bearings (the ones at the back that resist pressure when moving wood into the blade). On the 12", it was a sleeve bearing, on it's side, so the blade was pushing against the rim of it and not the flat part, and it wore grooves when the bearing stopped turning. This grooves tended to "worry" the blade and even heat it as I worked, softening the metal.
Cheap blades didn't help.

I'm not familiar with your model, but I'd check this and see what shape they're in. Sears typically used an inexpensive (unless you buy it through them) bearing, nearly identical to roller skate bearings, which can be had rather cheaply on Ebay.

This resembles what it looked like:
https://s3.amazonaws.com/vs-lumberjocks.com/nv21chn.jpg

[Carroll Courtney]

If your saw has thrust bearings make sure they are just barely touching and make sure you have your guides adjusted.Which I believe you done all this since you haven't had issues in the past but its worth a second look-------Carroll

[Yonak Hawkins]

It could well be blade quality. I had a spate band saw blade breakage with at least 3 different suppliers awhile back.

[Lee Schierer]

Have you changed brands recently? What brand blades are you using? Is your tensioning spring bottoming out when you tension the blades?

[dennis thompson]

Have you changed brands recently? What brand blades are you using? Is your tensioning spring bottoming out when you tension the blades?

I'm getting the blades from Suffolk Machinery. Do you think I might be putting too much tension on the blades? How would I determine the proper tension?

[Wayne Lomman]

Heating the back edge of the blade through running hard on the thrust bearings is a common cause. Too much tension can do it too. Have just enough tension to cut true and drive properly and no more. Cheers

[John K Jordan]

I'm getting the blades from Suffolk Machinery. Do you think I might be putting too much tension on the blades? How would I determine the proper tension?

Dennis,

If you can borrow a bandsaw tension gauge you could check quickly. You can improvise one for no cost if you have some digital calipers:

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From John TenEyck

(Measuring tension with digital calipers)
...the blade guides are removed or at least backed away from the blade. Clamp the vernier with about a 5" gage length so that each jaw is on the flat of the blade, between two teeth. On really narrow blades it's best to face the vernier towards the back of the saw in order to avoid the teeth altogether.

The basic calculation is Young's Modulus = Stress/Strain, where:

1) The Young's Modulus of steel is about 30 x 10^6 psi.
2) Stress, the value you are after - the tension in the blade in psi.
3) Strain = Deflection / gage length. The vernier measures deflection, and the gage length is the starting distance between the jaws under zero load.

So, you rewrite the equation as Stress = Young's Modulus x Strain = 30 X 10^6 x deflection/gage length

The gage length I started with was 4.768", so when I measured a deflection of 0.003" that was equal to a blade tension of 30 X 10^ x 0.003/4.768 = 18,876 psi.

My little Delta was more than maxed out with the 1/2" blade I was using. The Iturra spring was nearly fully compressed, the frame was distorted by nearly 0.010" and that pulled the upper guide completely out of alignment. The data showed that I can't really run more than about 12K psi on a 1/2" blade. But with a 1/4" blade I can run at nearly 25K psi w/o over stressing the saw. The 1/2" blade will still cut OK at 12K psi, but I have to run more slowly than I would if I could apply higher tension to avoid blade deflection.

bandsaw_tensioning_TenEyck.jpg
bandsaw_tensioning_TenEyck.jpg

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JKJ

[Lee Schierer]

I'm getting the blades from Suffolk Machinery. Do you think I might be putting too much tension on the blades? How would I determine the proper tension?

You should read their tension instructions

[dennis thompson]

You should read their tension instructions

Lee,
Thanks for your suggestions.
I did read the Suffolk tension instructions and I watched the Alex Snodgrass bandsaw video. I tuned up the bandsaw, and eased the tension a bit, so far so good.

[glenn bradley]

I'm getting the blades from Suffolk Machinery. Do you think I might be putting too much tension on the blades? How would I determine the proper tension?

If they are the silicon steel blades they require very little tension. This may be in direct conflict with wanting to use them for scroll work. If you have always been using them then I would try to determine what has changed at your end. Different guides or a different way of setting them? Tighter curves on wider blades (1/4" instead of 3/16" or the like)? I bury my small blades in "Cool Blocks" (they make them for a variety of saws) and this seems to work well for my on my 10" saw. I have seen other folks use small blocks of wood to allow the blade to 'worry' a path into the guide while scrolling.