Why do bandsaw blades break?

Seems my DeWalt portable bandsaw causes blades to break prematurely.
They just crack with a telltale clacking/clicking sound, meaning it must be
stopped and the broken blade changed, or risk the bandsaw coming to a jolting halt when the broken blade catches on something.
I hardly use the thing, unlikely it's from normal wear. It has gone through three or four blades, about one per session of light use.
I usually cut small pieces of 1/8-1/4 inch thick aluminum (6061).
I bought the larger version, so this problem will (hopefully) be moot soon. But I would like to know. Maybe using the larger version will provide evidence on whether it's the saw's fault. But the large one needs a stand, waiting on the metal plate for that.
Thanks.
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John Doe wrote:

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
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On 14/12/2020 03:18, Jon Elson wrote:

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.
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wrote:

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
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David Billington wrote:

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
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"Jon Elson" wrote in message ................ 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 ----------------------------
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.
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On 12/13/2020 2:03 PM, John Doe wrote:

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.
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Bob Engelhardt wrote:

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.
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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.
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Or maybe DeWalt's small bandsaw (DCS371) is a crap tool. Maybe they are in disfavor with the Chinese Communist Party and their tool quality is going downhill as a result of that. Or maybe I got a lemon.
In any case, it sucks. No twisting. Cutting a straight line. DeWalt blade (shipped and sold by Amazon) still cracked after minimal use.
Hopefully my bigger DeWalt portable bandsaw (DCS374B) works better. But it has apparent signs of being at least partly designed in China (besides being manufactured there). Will be wary if I purchase anymore of theirs.
They have also developed that stupid practice of practically welding their drill chucks to the spindle.
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"John Doe" wrote in message
Or maybe DeWalt's small bandsaw (DCS371) is a crap tool. Maybe they are in disfavor with the Chinese Communist Party and their tool quality is going downhill as a result of that. Or maybe I got a lemon.
In any case, it sucks. No twisting. Cutting a straight line. DeWalt blade (shipped and sold by Amazon) still cracked after minimal use.
Hopefully my bigger DeWalt portable bandsaw (DCS374B) works better. But it has apparent signs of being at least partly designed in China (besides being manufactured there). Will be wary if I purchase anymore of theirs.
They have also developed that stupid practice of practically welding their drill chucks to the spindle. --------------------------------------
Perhaps the saw needs a trigger actuator headspace adjustment.
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    Maybe *you* are not twisting the blade, but the design causes the blade to be twisted (about 45 degrees -- I don't have one here to measure) as it spools off one wheel, is twisted by the guides to orient the blade vertical to the workpiece, and then untwisting it just before it spools onto the second wheel. The disance between the wheels and the blade guides is pretty small on that little bandsaw, so it likely stresses the steel more than the larger one. (Try measuring the distance from exiting the wheel until it enters the guide. I'll bet that it is significantly smaller on the smaller saw -- thus more flexing of the blade back and forth. The import horizontal/vertical 4x6" saws are bigger, and with the adjustable blade guides, are usually a greater distance from the wheel.

    I would expect it -- just because it does not twist the blade in as short a distance from wheel to guide.

    Isn't everything manufactured there these days?

    Reversible spindle? If so, it should have a left-hand screw in the center of the chuck and threaded into the spindle. *NOTE* -- I said left-hand screw. This is so the chuck does not unscrew from the spindle when running in reverse.

    Good Luck,         DoN.
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"DoN. Nichols" wrote:

Apparently some manufacturers are being ripped off more than others. Depends on what the Chinese Communist Party wants. One would think their goal is to eventually consume and/or control everything.

They stopped using a screw. Now they use a press fit. It's impossible to remove without cutting through the chuck. I'm not into using a torch, but maybe that would work.
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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.
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wrote in message wrote:

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.
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    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.
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"DoN. Nichols" wrote in message .... 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.
------------------------- 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.
https://pat7.com/js/4x6bsFAQ.html
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.
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On 12/19/2020 10:00 PM, DoN. Nichols wrote:

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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"Bob Engelhardt" wrote in message
On 12/19/2020 10:00 PM, DoN. Nichols wrote:

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.)
-----------------------------------
Do your blades break?
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"DoN. Nichols" wrote in message ... Hmmm ... perhaps a low profile thrust ball bearing under the knob might help. ===========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.
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