Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Default 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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Default Why do bandsaw blades break?

John Doe wrote:

Seems my DeWalt portable bandsaw causes blades to break prematurely.

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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Default Why do bandsaw blades break?

On 12/13/2020 2:03 PM, John Doe wrote:
...
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).
...


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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Default Why do bandsaw blades break?

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

Seems my DeWalt portable bandsaw causes blades to break prematurely.

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


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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Default Why do bandsaw blades break?

On Mon, 14 Dec 2020 21:25:41 +0000, David Billington
wrote:

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

Seems my DeWalt portable bandsaw causes blades to break prematurely.

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


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

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Default Why do bandsaw blades break?

Bob Engelhardt wrote:

John Doe wrote:


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).


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.


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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Default Why do bandsaw blades break?

David Billington wrote:

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

Seems my DeWalt portable bandsaw causes blades to break prematurely.

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


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.

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 2020-12-13, John Doe wrote:

Seems my DeWalt portable bandsaw causes blades to break 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.


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wrote in message .. .

On 2020-12-13, John Doe wrote:

Seems my DeWalt portable bandsaw causes blades to break 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.


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---------------------------

Usually there is no indication of tension and all the user can do is follow
the manual's instructions. The tension counteracts the blade's tendency to
deflect back and twist sideways in the cut. It has to twist if forced to
bend back, once the tooth edge goes into compression it has no other choice.

The recommended tension for the sawmill blades I use is 22,000 PSI, which
amounts to 1000 Lbs per side, or 2000 Lbs pushing on the wheel axle, since
the gullet cross-sectional area is 1/22 inch. The motorcycle tires (and
presumably the alloy wheels) are rated for only about 1/3 of that so I
compromise at 1000 Lbs pressing on the axle carrier, measured with a
hydraulic force gauge.



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On 12/13/2020 12:03 PM, John Doe wrote:
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.




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.


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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:
I would hope that it is adjustable for tension, ...


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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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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"Bob Engelhardt" wrote in message ...

On 12/19/2020 10:00 PM, DoN. Nichols wrote:
I would hope that it is adjustable for tension, ...


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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replying to John Doe, Factorial wrote:
From what I can tell on wiki https://en.wikipedia.org/wiki/6061_aluminium_alloy
The aluminum alloy you use is pretty sturdy and that could also be a potential
problem on top of what everyone else stated here..

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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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On 2021-02-08, Jim Wilkins wrote:


"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.


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.

Hopefully my bigger DeWalt portable bandsaw (DCS374B) works better.


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

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.


Isn't everything manufactured there these days?

They have also developed that stupid practice of practically welding their
drill chucks to the spindle.


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.

Perhaps the saw needs a trigger actuator headspace adjustment.


Good Luck,
DoN.

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"DoN. Nichols" wrote:

John Doe wrote:


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
blades (shipped and sold by Amazon) still crack after minimal use.


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.

Hopefully my bigger DeWalt portable bandsaw (DCS374B) works better.


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

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.


Isn't everything manufactured there these days?


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 have also developed that stupid practice of practically welding
their drill chucks to the spindle.


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.


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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