Snapped a bandsaw blade

[Callum]

Hi there, I'm after a bit of advice please. I was using an axcaliber 1/4 inch 10tpi blade on my bandsaw today to cut out some easter bunny shapes with the young lad in the house (yes we're stuck inside), and after the very last cut, and after turning the bandsaw off, I turned around and heard a very worrying bang, and I found that the blade had snapped. Luckily the blade never flung out at all, and we had both stepped away from the machine so no injuries or anything, but obviously I don't want to be in a position again, especially with the boy stood there if theres a risk of it snapping again due to something I might be doing wrong.

I'm just after some advice really, but i'm pretty sure the reason it snapped was something to do with the last cut off bit of wood, as it fell down towards the lower wheel and got stuck somewhere around the wheel and the blade instead of getting sucked away into the connected vacuum, and I'm guessing this put some strain on the blade somehow as the machine was slowing down?? The blade snapped about 10mm away from the weld so I didn't think it was a bad blade.

My questions really are, could I have over tensioned the blade at all, I always here about them being under tensioned but so far I've not found that an issue yet? Or was it the way I'd used the blade, I felt sometimes I may of tried to cut too tight of a turn when cutting the curves on the bunnies so was it the that may of weakened the blade?

Thanks.

These are the unfinished bunnies for those that might be interested :lol:

 

[AndyT]

First, don't worry. Bandsaw designers know that blades snap and build cases which contain the broken blade.
Second, to prevent little bits of wood falling down and getting stuck, you may need to make a new zero clearance insert. These vary with different models but are generally a bit of plastic or wood that fits closely around the blade. You may have one with a wide slot, which is only needed if you tilt the table. For 99% of work you can use something which fits better. Normally easy to make your own.

 

[Callum]

Thanks, it came with 2 inserts so i'll check the other one and see how it looks.

 

[Mike Jordan]

I don't often use blades as small as that but I have had a number break in use. I regard it as normal when the blade has done a lot of work, they are being constantly flexed from curved to straight while working. I think that a break close to the weld is also common, Ive assumed that this is a heat affected Zone and slightly more prone to failure.
Two things which sometimes preceded a break are a ticking noise from the blade or a slight front to back oscillation in use. If you stop at this point it is possible to see a crack opening up in the blade. As already mentioned the modern machine keeps the broken blade safely inside. The only risk I know of is the possibility of opening the door while the top wheel is still rotating.

 

[worn thumbs]

The biggest risk of the blade flying off the machine is not having the top guide as low as it should be.If you keep it close to the job the broken blade doesn't have the distance to allow it to move sideways very far and it stands a much better chance of being contained.

 

[sunnybob]

My bandsaw gets used hard. I have broken several (almost many) blades and they have all stayed safely inside the machine regardless of the height of the blade guard.

As mentioned above, if a blade breaks, be VERY CAREFUL opening the doors. The lower one will stop straight away because its connected to the motor. The top one is a free wheel and will spin at high speed for a long, long time. Try to stop that with your hand and you will lose it. I use a long stick of wood and slowly press against the rim of the wheel to slow it down.. Push on the rear side of the wheel as its climbing, not as it comes towards you or you will be unpleasantly surprised.

A simple way to get the blade correctly tightened is to adjust it tight (with the power disconnected) untill you can almost turn the blade 90 degrees by hand. Then start it up and while watching the blade from the front, tighten it untill it stops fluttering and becomes completely still.

 

[Trevanion]

It's an even more horrific experience to have happen whilst you're cutting! But not an overly common one.

If the blade in under quite a bit of tension it's surprising how a little off-cut getting caught between the wheel and blade will either take the blade off the wheel or rupture the blade, especially on thinner blades such as the 1/4 you were using.

What Andy says is totally correct, blades tend to snap inside the machine and can be a right pain to remove if they crumple up against guarding or the casing. I've snapped quite a few down to pushing them beyond their lifespan, I've only ever once had a blade snap where it slid across the table to the outside right-hand side of the machine. That was enough to make me a bit more thoughtful about where I'm putting my hands whilst cutting, especially with a blade on it's way out.

 

[Mike Jordan]

As an apprentice I worked in a shop that had an old bandsaw about 8 foot tall, the blade was fenced in the cutting area but could be seen running round the top cast iron wheel. When I took things to be cut by the machine operator he advised me not to stand to his right in line with the wheels outside edge, just in case the blade broke in use and came in that direction.

 

[TheTiddles]

My bandsaw gets used hard. I have broken several (almost many) blades and they have all stayed safely inside the machine regardless of the height of the blade guard.

As mentioned above, if a blade breaks, be VERY CAREFUL opening the doors. The lower one will stop straight away because its connected to the motor. The top one is a free wheel and will spin at high speed for a long, long time. Try to stop that with your hand and you will lose it. I use a long stick of wood and slowly press against the rim of the wheel to slow it down.. Push on the rear side of the wheel as its climbing, not as it comes towards you or you will be unpleasantly surprised.

A simple way to get the blade correctly tightened is to adjust it tight (with the power disconnected) untill you can almost turn the blade 90 degrees by hand. Then start it up and while watching the blade from the front, tighten it untill it stops fluttering and becomes completely still.

Got to say, you really don’t need to do anything to stop the top wheel, just wait! Don’t open the door, just wait.

Breaking blades is fine, the bang can be a surprise but that’s really all there is to it. It’s fine and safe.

If you’ve monkeyed with the machine safety features it could be dangerous, but then that’s your own silly fault.

Aidan

 

[Callum]

It definitely made me jump when it went haha! Thanks for everyone's advice, I did leave it a while before opening the door because I could hear the wheel slowing down, it had almost stopped, and the blade guides were close to the wood when cutting.

So chances are I hadn't done much wrong then, apart from the insert having too big of a gap next to the blade. I'll check the other that came with the machine or make one. Can you over tension the blade at all as well? It's hard for me to gauge without a bit of experience yet, but using the 1/2 inch blade I had set up before this smaller one, I pretty much got as tight as I dare go, and I'd read or watched somewhere if you pluck the blade it would sound nice, not dull or muted if that makes sense? Did the same when setting up the small one.

 

[woodbloke66]

Got to say, you really don’t need to do anything to stop the top wheel, just wait! Don’t open the door, just wait.

Breaking blades is fine, the bang can be a surprise but that’s really all there is to it. It’s fine and safe.

If you’ve monkeyed with the machine safety features it could be dangerous, but then that’s your own silly fault.

Aidan

Spot on. It's a bit a shock when a blade does break 'cos it makes a hell of a 'bang' but as Aidan has said, it all happens inside the machine and is perfectly safe. Simply wait until everything has come to a halt, open the door(s) extract the old blade and replace with a new one, giving the interior a good clean at the same time; job done.
What you should always do at the end of each working day in the 'shop is to release the pressure on the blade as it prevents deformation of the rubber wheels. As to pressure, I always crank my blades up to maximum and as long as the pressure is released at the end of the day, no harm is done to the machine - Rob

 

[deema]

Just a different view and experience, the driving wheel at the bottom tends to ensure that blades with a small width stay in the machine, however wide blades have a nasty habit of snaking out of the machine. They tend to go sideways To the right and hopefully onto the floor.

Never stand to the open side of a Bandsaw, and never out your hands up to and either side of the blade feeding stuff through.

 

[Vann]

...When I took things to be cut by the machine operator he advised me not to stand to his right in line with the wheels outside edge, just in case the blade broke in use and came in that direction.

I was also told (as an apprentice) not to stand to the right* of the blade - in case it broke.

I've passed that advice on to the younger (teenage) daughter - the only one of my offspring with any interest in what I do in my workshop.

Cheers, Vann.

* or to the left in the case of a left handed bandsaw.

 

[Max Power]

Has anyone been injured by the blade of a small bandsaw snapping :?

 

[Doug71]

What you should always do at the end of each working day in the 'shop is to release the pressure on the blade as it prevents deformation of the rubber wheels.

Do many people do this, the only time I ever release the tension is when I'm changing a blade?

It was discussed recently on another forum and I reckon about half released the tension and half didn't.

 

[Trevanion]

Has anyone been injured by the blade of a small bandsaw snapping :?

I've never heard of anyone actually being injured as a result of the blade snapping, but I certainly wouldn't want to be in the path of the blade when it does come out.

I was shown some photos once from a large workshop in the 70s or 80s where the blade had snapped on a big re-saw (Something like a 3" deep blade) where there was nothing containing it on top of the top wheel, and it went through the roof of the workshop and was dangling about in the wind outside :lol:

 

[deema]

I never leave the tension on the blade. It causes the rubber on the wheels to take a set which creates reduced tension in the blade / inaccurate cutting.

 

[marcros]

I don't. On the rare occasion that I have it has resulted in a very poor next cut because I forgot to retention it.

My bandsaw has a lever for this, I don't know if that is a common feature.

 

[Trainee neophyte]

Mine says specifically in the manual not to relieve the tension. Perhaps it will go blind?

 

[mbartlett99]

Not releasing the tension just increases the chance of damage to your bearings - think of flat spotting a tyre. Depends on the quality of bearing and the amount of tension. Personally I do release when I'm done.