Bandsaw blade broke.

[iublue]

I have never had this happen before when I had my old 32" cast iron monster. This morning I was resawing and step away to get another piece of wood and BANG, the blade broke. Since I would rather not have that happen again , I would like to ask the collective data bank here some questions.

I have a MM20 saw. I realize the blade turning around a 20" wheel instead of a 32" wheel will be stress the blade differently. I had an 1 1/4" carbide tipped resaw blade on it. I do not know the brand since it came with the saw. I bought the saw used. I do not know the age of the blade. The only thing I could read on the blade was Sweden.

I had tensioned the blade using a dial indicator clamp to the blade and a piece of wood clamped to the blade ~12" apart. I tensioned the blade to .010 amount of stretch. That should be 25,000 psi according to this article. http://www.solowoodworker.com/tools/resaw.html

So, did I have too much tension?

I do not detension the blade. Should I? Could this have contributed to the failure?

What about blade lubrication? Could this have been a factor.

Any and all information will be appreciated.

TIA

Toney

[daddo]

Been many years since I've done this. I just tighten a bit by feel and go now.

Perhaps I remember some. Correct me if I'm wrong.

The standard was to test at 5" on the blade, and typical was .001", .002" and .003" stretch and then double that since both sides of the blade is stretching- then use the blade size calculations for psi.

Your .010" seems like a lot of stretch. But that depends on if you are doubling it or not and what the manufacturer wants.

[Robert Adams]

It happens. Always detension the blade if you have a lever to do so.

[iublue]

Robert Adams said:

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It happens. Always detension the blade if you have a lever to do so.

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The MM20 doesn't have a lever. I guess I could take a turn or two to loosen it and then the same amount to use.

[doobes]

Robert Adams said:

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It happens. Always detension the blade if you have a lever to do so.

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I suspect that there was a fault in the blade weld. I've never had one break on me without being abused

I've never detensioned the blade on my 16" Walker Turner. Don't think it's necessary, at least for this saw.

[thewizzard]

If you use the machine daily there may be some argument for not relaxing the blade after each use. Don't forget that there are more parts involved in the saw than just the blade. Leaving the saw fully tentioned and idle can eventually cause uneven tires and wheel bearings. For my semi-infrequent use, I back off the tension after every session. I've never been in such a hurry that I couldn't find 5 seconds to turn a big knob a few rev's.

[jteneyck]

+1. I never used to take the tension off my saw either, until it started vibrating. Then I realized the tires were either getting a flat spot in them or squirming on the wheels from sitting so long between uses. After I started taking half the tension off the problem went away and it runs nice and smoothly again. I keep the instruction manual with the machine. When I take the tension off I hang them on the top cover to remind me to re-tension before using it the next time.

I had two Timberwolf blades break; neither was at the weld. Neither had been abused and both were tensioned per Timberwolf's low tension, flutter method. I had another blade break, also not at the weld. Over tension wasn't the issue there either. It was a 1/2' blade and my saw is a 14" Delta. You couldn't over tension that blade if you wanted to. Blades can and do break, and not just at the weld.

John

[jteneyck]

The math in the link is correct, so if you had 0.010" strain over 12" then you had 25,000 psi on the blade. Blades break for lots of reasons. You don't know how old the blade was. It could just have been it's time.

As mentioned, taking the tension off the blade when you aren't using it is never a bad thing.

John

[Ken Vick]

jteneyck said:

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The math in the link is correct, so if you had 0.010" strain over 12" then you had 25,000 psi on the blade. Blades break for lots of reasons. You don't know how old the blade was. It could just have been it's time.

As mentioned, taking the tension off the blade when you aren't using it is never a bad thing.

John

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Well, unless you are the kind of person who will then go back into the shop and restart the saw without tensioning it again. BTDT. Not good. My blades usually last for years even under constant tension. Ken

[mike4244]

I'll preface my remarks by saying My bandsaw is a 16" Grizzly,not an expensive saw like yours. I tension my blades,they are low tension type blades by pushing the blade til I get 3/8"deflection. I do this on the column side of the saw.I believe this is the most common way to tension a saw without gauges.
I read the link about tensioning blades with an indicator.Until I read the link I did not know the difference between low and high tensioned blades.
Maybe your blade is a low tension blade and 25000 PSI is too tight.
Where did the blade break? If at the weld the tension might have been too much.I have sawed thousands of boards over the years,sharpen 3TPI or less blades many times with a Dremel tool .
Sometimes the blade will break because it has fatigued. Time to throw it out if the blade has been sharpened many times and finally breaks.
If your blade looks decent try hard soldering it if you have the experience.Takes practice though. Before you install another blade make sure you know if it is a high tension blade.If it is then the procedure you did should work.

mike