Bandsaw blade breakage

[Lard]

Here’s my penny worth…..many years ago I bought my first bandsaw (small bench top version), did some setup research and proceeded to use it……snapped 2 blades within days. Being my first experience of using a bandsaw it scared the shyte out of me (the unexpected ‘bang’ etc).
Did a lot of online reading and, funnily enough, ended up joining this forum simply to ask the exact same question as the OP. Based on the advice I was given, I ended up both increasing the tension and being introduced to Tuffsaws, from whom I bought 3 new blades.
However, the problem did not go away and I very quickly snapped the 3 blades and, similarly again to the OP, it was again suggested that my tension still wasn’t high enough.
Got to the point where I was afraid to use the machine as the tension was that high that when it ‘went’….boy, you‘d feel your heart in your chest!.
As a last resort (I seriously thought about selling the machine) I sought out a local wood turning group for help. The instructor gave me a wealth of ‘over the phone‘ basic advice but the results didn’t change. In desperation I persuaded him to come out and have a look at the machine.
The VERY first thing he said was something like “bl**dy hell! you have way TOO MUCH tension on the blade“. He slackened it off to a level that was somewhat completely opposite to the amount I had. He reset the wheel and the guides and proceeded to give me a lesson….one in which had me wincing at the tightness of the curves he had me cutting (bear in mind I’d lost all confidence at this point)….he showed me/proved to me that in a worse case I would only STOP the blade and not snap it.
Long story short…..YEARS later I’ve only snapped two more and that was, I believe, simply due to fatigue.

Obviously blade tension is important and I still read about ’increasing it’ advice…..however, in my own case/experience the problem was solved by doing the opposite.

 

[pgrbff]

That is what I assumed! But they've told me almost the opposite. See last post.

I have always read that most saws, especially the smaller ones, are unable to provide the tension required for a good cut, I assume that is why one can buy thinner blades that need less tension. If this is true then I would also guess that it was more likely to be too little rather than too much tension.
4 months of use does not seem an unreasonable amount but I guess that also depends on how hard and how thick the material was and if you were cutting for a couple of minutes or a couple of hours a day.
If it took 4 months of daily use to crack that doesn't sound too bad to me.

 

[Spectric]

An issue I find with the bandsaw is that unlike the mitre saw which is more forgiving when it comes to blades, teeth etc the bandsaw blades cut a more limited range of material and so need to be changed more often to another type, so how many people take the lazy option and just don't bother. I found using standard blades on ply and MDF certainly took the edge of them, now I use the M42 blades on man made goods and they last a lot better and are worth the extra cost.

 

[Ttrees]

I wonder if there's much camber on this saws wheels, and if that could be a problem running that wide blade.

I follow a lot of bandsaw folks on the creek, and John TenEyck being one of them.
He has an industrial 17"saw, @280kg
The saw has cambered tires and he runs very wide blades on them, tensioned to 2500K PSI for resawing, and he also sharpens his blades, not just touch ups.

Perhaps your tires have a lot more pronounced of a camber than the Griz he has?

Some interesting points I've read about tensioning.
TBH I thought his saw was heavier than that, and presumed the screw was a heftier one,
as IIRC, John has mentioned that just one half turn can mean the difference between tensioned to spec, and enough to snap the blade.
I think it may have went from 20 to 40k PSI very quickly.
Not that may be of interest here, as it's strictly resaw figures on a capable machine, but I think worth reading up a bit on his blog if any heavy work is foreseen.
https://sites.google.com/site/jteneyckwoodworker/

 

[Jacob]

Here’s my penny worth…..many years ago I bought my first bandsaw (small bench top version), did some setup research and proceeded to use it……snapped 2 blades within days. Being my first experience of using a bandsaw it scared the shyte out of me (the unexpected ‘bang’ etc).
Did a lot of online reading and, funnily enough, ended up joining this forum simply to ask the exact same question as the OP. Based on the advice I was given, I ended up both increasing the tension and being introduced to Tuffsaws, from whom I bought 3 new blades.
However, the problem did not go away and I very quickly snapped the 3 blades and, similarly again to the OP, it was again suggested that my tension still wasn’t high enough.
Got to the point where I was afraid to use the machine as the tension was that high that when it ‘went’….boy, you‘d feel your heart in your chest!.
As a last resort (I seriously thought about selling the machine) I sought out a local wood turning group for help. The instructor gave me a wealth of ‘over the phone‘ basic advice but the results didn’t change. In desperation I persuaded him to come out and have a look at the machine.
The VERY first thing he said was something like “bl**dy hell! you have way TOO MUCH tension on the blade“. He slackened it off to a level that was somewhat completely opposite to the amount I had. He reset the wheel and the guides and proceeded to give me a lesson….one in which had me wincing at the tightness of the curves he had me cutting (bear in mind I’d lost all confidence at this point)….he showed me/proved to me that in a worse case I would only STOP the blade and not snap it.
Long story short…..YEARS later I’ve only snapped two more and that was, I believe, simply due to fatigue.

Obviously blade tension is important and I still read about ’increasing it’ advice…..however, in my own case/experience the problem was solved by doing the opposite.

My experience too.
Most breaks in the bad old days were at the weld itself - which meant poor welding.
I've been using Tuff saws with no prob (they are as good as people say) and not inclined to increase tension while they are cutting OK.

 

[pe2dave]

2500K psi?
20-40K psi? How do you measure 'pressure' on a bandsaw?
Perhaps if there was a reasonable way to measure tension we could set our saws to 'the correct' tension for... is it the saw or the blade?

 

[pgrbff]

2500K psi?
20-40K psi? How do you measure 'pressure' on a bandsaw?
Perhaps if there was a reasonable way to measure tension we could set our saws to 'the correct' tension for... is it the saw or the blade?

You use a bandsaw tension gauge, which costs a fortune. I 3D printed mine. This isn't mine but otherwise the same. Mathias Wandel? also made a wood one.

 

[clogs]

I'd say to the inexperienced.....
nip up the tension on the blade from slack to just NOT slack and then turn the adjustment
1/4 of a turn until happy ....using paint or tipex marks to repeat the same.....
it just takes time and experience to get consistant tension.....

Lard had the right idea, ASK someone with experience.....
Surley there would be someone on the forum nearby that will help u out....
U just got to ask.....this is a good place/forum to be.....

 

[pe2dave]

And then repeat for each blade you own? Surely 1/4 turn depends on the machine you have?
Lots of magic incantations around the net, None I've found work reliably for different blades?
(Equally I've not had a blade snap - perhaps I've too cautious?)

 

[pops92]

I have always done the flutter test.
Never failed me and I get get very few breakages and as I have had blades that are slightly larger the tension gauge is no use.
I showed this to a guy who had little knowledge on a bandsaw and he use this method and no breakages.
As others Tuffsaws is my choice of blades

 

[baldkev]

On my kity ( which had new tyres, but turned out they werent thick enough ) i couldnt get it to cut straight in anything over say 20mm oak.... straight cuts against the fence etc, wandered in both directions. After finding the issue and sorting the tyres i could apply much more tension and it much improved.

Im waiting on some bits for my new bandsaw, then I'll be able to test it out.
I guess trial and error....

 

[baldkev]

I have always done the flutter test.
Never failed me and I get get very few breakages and as I have had blades that are slightly larger the tension gauge is no use.
I showed this to a guy who had little knowledge on a bandsaw and he use this method and no breakages.
As others Tuffsaws is my choice of blades

I'll give that a go

 

[Peter Sefton]

It is generally excepted that it's better to over tighten than not to have enough tension on a blade, blades will last longer with higher tension but the issue can be strain on the bandsaws structure. If you over tension blades on light weight bandsaws you can bend or put the frame in twist. Thinner gauge blades require less tension and are better for lighter weight frames, M42 blades are thicker and require more tension so need to be avoided on smaller bandsaws and they also do not cope well with small diameter wheels.

Blade selection is one of the topics covered in this DVD/download I made a few years ago, from memory I also covered the flutter method but I am not keen on this as I think it's dangerous and can damage the blade rattling with the bandsaws column.

https://woodworkersworkshop.co.uk/peter-sefton-ultimate-bandsaw-set-up-and-maintenance-download/

 

[dzj]

A method I use is to lift the blade guide in the upper-most position, tighten the blade so that when
you push the blade laterally (with moderate force), it flexes about half a cm.
It's a very scientific, hi-tech method.

 

[Ttrees]

2500K psi?
20-40K psi? How do you measure 'pressure' on a bandsaw?
Perhaps if there was a reasonable way to measure tension we could set our saws to 'the correct' tension for... is it the saw or the blade?

Sorry that should read 25 000 PSI (not great with numbers myself)
Not ever tried to measure, just noting that's what a highly tensioned blade is,
and that this is for max capacity resaw with a decent machine.
From what I've read, most saws would fail to tension a 3/4" blade of moderate gauge
thickness, as the spring being the first to fail at figures around 15 000 PSI.
This is the impression from the American forums mainly and talking about saws between 16" to say 24" machines, and 3/4" to 1" blades.

TBH I'm just waiting for someone to make a good video of a very similar blade to what I'm using, and do the ping test and some sort of easy deflection test, without making a jig, as I won't need be resawing at max capacity for a long time yet.


Regarding the travel of the screw, and the possible importance of it at times...

I'll have to dig to make sure it was John who said this, and posted those figures, just for accuracy sake.
If it is John who said this, then seems to me worth noting, as that screw I don't believe is a double start thread, which I guess is twice as fast.
Compare that screw to an Italian machine, with bigger faster threads and that instance becomes more likely that it might happen.

Just noting this, as with narrow blades it might not take much to over tension them.

EDIT: to add a quote from John, hope he doesn't mind.

"Using this gage I found that the difference between applying 25 ksi to a Woodmaster CT and 42 ksi is surprising little. At 25 ksi the arrow on the saw's tension indicator was just below the 1" blade mark while at 42 ksi it was just above it, less than 1/2 a turn on the tension wheel."

 

[TheTiddles]

PSI isn’t just for fluids, it’s a force over an area and will be relative to the material under load, so a smaller blade may still need the same “pressure” but as the cross-sectional area is smaller, that can be achieved with less force being exerted by the spring.

You can’t measure it directly, but you could measure the compression length of the spring and construe the force it is exerting and then compare that with the area of your blade.

I bought a bandsaw with a broken tension gauge so I’ve not a clue, but I did do a small new blade up less than I would my usual big rip blade and it broke after not very long.

 

[RobinBHM]

Having spent years with resaw wide blade bandsaws and narrow blade bandsaws, one becomes tuned into blades about to go.


there are 2 indications:

1) a “ticking sound”

2) blade starts to wobble forward and back.

A 3“ resaw blade makes a Big Bang when it goes, and usually needs a grinder to get it out of the machine so best avoided.

 

[MARK.B.]

I use a 3/4 on my Sip 14" that is not exactly the best money can buy i know and to be fair it sat somewhat sadly in a corner for a few years as i just could not get it to run right until I got the right blades and the difference was use it all the time now and the 3/4 stays on almost all the time

 

[Flynnwood]

+1 for Ian at Tuffsaws.
Gives great advice and even offered to re-weld one for me free because, I might have over tightened it.

 

[ivan]

Our tension guage is made from a £9 Aldi digital caliper. The 2 jaws are each clipped to the blade so the caliper measures the stretch in the blade over the distance between them. The general arrangement was outlined in Fine Woodworking 147 some years ago. You measure the extension due to tension over about 5 inches of blade.
You ignore the gullet, so a 1" blade is taken as 0.75" x 0.035" in cross section (=0.026sq inch) which is a lot less than the 1 sq inch in 25,000 psi (lbs per sq inch) for a bi metal blade. The saw then has to provide something over 600 lbs tension in the blade, which is in a loop, and so double this in the spring. That produces about a 4-5 thou extension over the 5" (for 25-30,000 psi)
A 1/2" 3tpi blade might be about 0.35"x0.025", to tension a spring steel blade (15,000psi) equates to aver 100 lbs in the blade, so about 250 lbs in the spring. For more tpi = shallower gullets the x section is a bit bigger, so the spring load will be higher. The amount of tension is the same for all sizes of blade of the same type.

FW's home made guage (4 7/8"), or my Aldi caliper, both measure over about 5", when the blade will stretch around 1 thou per 6,000 psi applied. For a spring / carbon steel blade you want a stretch of about 3 thou = 15,000 psi. FW recon theirs is accurate +/- 10% which isn't bad.

Our saw is one of Axies 18" models, which was supposed to take blades up to 1 1/4". You can get one in, if you like Chinese wire puzzles, but 1" is the practical everyday limit. It will just about tension 3/4" bimetal blades to spec, or 1" spring steel which has a lower reccomended tension.

If you see multiple cracking, probably the wheels have too small a diameter for the thickness of the blade, unless the blade is very old. Multiple cracks suggest metal fatigue from too much bending.