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.

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

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.

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.

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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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.

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

"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.

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.


--

SDF Public Access UNIX System - https://sdf.org

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.


--

SDF Public Access UNIX System - https://sdf.org

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

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.