Why do bandsaw blades break?

The shorter the blade, the more revolutions per minute it makes over the wheels. That constant straightening/bending fatigues the metal. My blades usually break at the weld, showing that my blade welding is not as good as it should be.

Anyway, a giant 6 foot tall saw ought to have blades that last longer than a portable one. That's just expected.

Jon

That is extremely unusual. My 1st guess would be cheap blades. You don't need bi-metal for aluminum, but don't cheap out either.

2nd guess is operator error. Most likely is twisting the blade in the cut. Around either axis - I hope you get what I mean 'cause it's hard to explain. Thinking about it- this is more likely the problem than blade quality.

Without having done the bending calculations I'm inclined to think the stress in the blade will be well below the fatigue limit for the material so should go around indefinitely without breaking. All the blade breakages I've had had a root cause such as tooth damage which results in the blade getting hammered in that area till it breaks. I normally use Lenox bimetal blades and they seem to last well.

My bandsaw blades tend to break in random places. Once a blade breaks if I examine it carefully it will show several places where cracks are starting to form. These cracks usually are not associated with any other obvious defects, such as broken teeth and are close to perpendicular to the length of the blade. Broken teeth could be the cause of some breakages but I hardly ever have teeth break on my band saw blades. Usually the cracks will run the entire width of the blade but of course they are not very deep. This makes me think that the blades are very well made, very uniform, because there will be several cracks just starting to form, all at about the same time. Eric

I try to cut a straight line by rotating the piece left and right to keep it on track. Being a 1/2" wide blade, that causes the blade to twist. Seems strange it is so sensitive, but that twisting theory is easy enough to prove. Will also use a guide when possible. The blades are all good.

I have one of those horizontal-vertcal bandsaws, so the blades not only go around the wheels, they get twised about 45 degrees in the cutting region to cut straight. I think that puts a lot more stress on the blade than on a big wheel vertical-only saw. Also, the smaller the saw, the smaller diameter the wheels are. That increases the bending.

Jon

Jon

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The 4" x 6" H/V bandsaws take blades 0.025" thick, and on mine they wear dull without cracking. Typically one side dulls more than the other so they deflect and cut crooked in thick wide stock, though they can still be used on smaller pieces.

I tried 3/4" wide x 0.032" thick blades on a 10" wheel upright bandsaw and found that they soon began to crack in the narrow part of the gullets.

The maker of the 1-1/4" x 0.042" blades on my sawmill recommends 19" or larger wheels for them.

I read this whole thread and no one mentioned blade tension. I'm not familiar with that bandsaw so don't know if tension is even adjustable, but over tensioning will certainly cause blades to fail prematurely.

I read this whole thread and no one mentioned blade tension. I'm not familiar with that bandsaw so don't know if tension is even adjustable, but over tensioning will certainly cause blades to fail prematurely.

On 12/13/2020 12:03 PM, John Doe wrote: > Seems my DeWalt portable bandsaw causes blades to break prematurely. >

I break some blades, but usually I dull them when I need to cut anything harder than mild steel for very long. Long before most will break. On my upright wood bandsaw all breakages are from getting in a hurry and binding the blade. I have not broken one on my upright metal cutting bandsaw (yet), but I have dulled a fair number of blades. On the horizontals I think they break from fatigue due to excessive cutting pressure because I feel time is more valuable than bandsaw blades.

Generally I buy Lennox or Starret bimetal blades for metal and WoodSlicer blades for wood. (Except for my little 4x6 bandsaw. The slightly more expensive Harbor Freight SuperCut bimetal blades are quite good on it. I just use that saw for backup nowadays though.)

P.S. I was amazed the first time I did some resawing with the Wood Slicer blades.

I would hope that it is adjustable for tension, since otherwise the fit of the blade would have to be unusually precise. Weid-your-own would be unlikely to fit. :-)

As for the 4x6 horizontal/vertical bandsaw, (lots of brands, all pretty much identical) -- it is very difficult to get the tension appropriately high. The knob on the tension screw is too small a diameter to allow applying enough torque. Essentially, tighten it as tight as you can manage, and it is likely not *too* far below the proper tension. Hmmm ... perhaps a low profile thrust ball bearing under the knob might help.

Good Luck, DoN.

Good Luck, DoN.

------------------------- I wonder if the frame / wheels / bearings are as inadequately sized as the tension knob. Maybe they knew the machine can't handle the proper tension and intentionally undersized the knob rather than redesign it.

I drilled two more mounting holes in the fixed vise jaw so I can place it very close to the blade to hold short pieces, or move it back to the original position to cut angles.

When I cut long stock out in the driveway I have to find a spot where both sides of the base contact the asphalt simultaneously when lowered or else it won't cut square vertically. The base casting isn't neatly stiff enough to resist twisting.

To support long stock I balance it on the saw and raise a jack to touch the outer end(s). Then the jack will be near the balance point when I move the stock to cut off an end. I've cut a smooth square end on 6x6 landscaping timbers this way.

The OP has a portable bandsaw, e.g., a "Portaband". I have the Milwaukee version and its tension is preset with a spring. (There's a lever to unload the tension for blade changes.)

One of the blades (33", for the small saw) looks like it has up to 40 cracks in it.

I will get around to testing the twisting theory, hopefully before moving on to the larger cordless saw.

Seems to me blade tension would be not so difficult to get right, using a lever (as they do) to release the tension. They probably can provide uniform tension for a certain small distance of wheel movement when the lever is restored to operating position. People familiar with spring tension should know that better than I do.

The OP has a portable bandsaw, e.g., a "Portaband". I have the Milwaukee version and its tension is preset with a spring. (There's a lever to unload the tension for blade changes.)

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Do your blades break?

Somewhere I read that a stack of greased alternating steel and brass washers makes a decent DIY thrust bearing. I tried it when I rebuilt my sawmill's blade tensioner to include the hydraulic force gauge.

The wrench handle effort for 1000 lbs is fairly low though too variable to use a torque wrench. The previous tensioner was the shaft and knob from a disk brake pad pusher and was difficult to tighten to 500 lbs.

Please get a real newsreader so you can legibly quote others...

replying to John Doe, Factorial wrote: From what I can tell on wiki

aluminum alloy you use is pretty sturdy and that could also be a potential problem on top of what everyone else stated here..

replying to John Doe, Factorial wrote: From what I can tell on wiki

aluminum alloy you use is pretty sturdy and that could also be a potential problem on top of what everyone else stated here..