Thread: Loud bang on bandsaw

It sounds like the tensioner might have some of lost its tension??

The blade came off the top wheel due to poor tracking. Possibly tension, possibly the tracking is actually changing due to vibration during use etc. As the blade comes off the top wheel, it folds over the edge of the wheel, extremely quickly, creating the kink in the blade. You can straighten it. Just bend it straight again with as little movements as possible so you don't work harden the area. When you reinstall the blade and get it to track properly again, sight the blade from the side and directly in front to make sure the blade is actually straight. If it is still kinked, even slightly, you will see a consistent wobble in the blade. you can use a kinked blade for a while before it actually breaks, but it does make life difficult.

I had a similar experience doing some work with my 12.7mm 3 TPI blade. At first I thought it was because I had fed too fast and things had sort of jammed momentarily, then as the wood broke, which it did quite spectacularly (the noise was almost like a rifle shot) I reached and hit the kill button.

Inspection revealed an almost identical bend/kink in my blade to yours. I have a sneaking feeling that I was getting tired, end of day and after a long session of cutting timber and fed the last piece in not quite on the saw bed. A catch, so to speak and the wood hit the deck causing the blade to jump and come off the bottom tyre.

At least that is what I think happened.

One aspect is that I took the blade off, then using a ball pein hammer on both sides I de-stressed the blade on my Triton super jaws anvil section. Although I have replaced that blade, I was able to continue using that blade until I received a new one. I still use it for green wood and rough stuff where there could be a possibility of a nail or stones.

Mick.

Thanks Optimark. It happened when I was 3/4 of the way through the last piece of timber, and I was holding the timber down with one hand on the outgoing side of the table, and pushing the end of the timber with the other with a bit of scrap timber; and the workpiece had a featherboard pressing it against the fence. And I was sawing quite slowly, letting it find its own rate of feed.

Don't think I will be trying to flatten the blade and put it back in service, especially as Kuffy indicated, the blade will break eventually.

Not sure how to stop this from happening again, but will be tuning the bandsaw with a new blade before I do any more cutting, including removing that build up of gunk on the centre of the wheel you can see in the pics

Let me guess ..... Laguna 14/Twelve with 19mm resawking ....

There have been numerous identical situations reported on this forum ...happened to me .... but my blade snapped like so many others have experienced.

My diagnosis is a bit different to others ... the 19mm resawking blade fits pretty well on the top wheel but the teeth overhang the edge of the lower wheel ..... saw this very thing at the Laguna wood show stand last month. The cause of my break was the teeth engaged the carrier for the black plastic blade cleaner ... snapped it in half.

Regards

Rob

Nearly right, Rob. Yes, a Laguna 14/12 but with a Henry Bros blade 19mm variable teeth spacing to reduce waterboarding effect.
Will be pulling it apart tomorrow. That is another thing to look for, thanks Rob

Pulled the bandsaw apart today, the 3/4" blade had snapped cleanly across the width of the blade, at a point about 120mm from the weld. Could not find any reason or possible cause. The break was on the left hand side of the saw, midway between the upper and lower wheels.

Fitted a 1/4" blade today to cut some curves, went like a charm

think you might have just answered your question.

A blade under tension will make a loud bang if it snapped, if your bandsaw is working fine after sticking a new blade on it doubt there is anything wrong with the bandsaw. Might have either been blade manufacturing fault or there was too much tension on the blade.

My Laguna SUV14 has snapped a blade exactly in this manner. A 1" Resaw king.

Like a shotgun blast it was!

For keeping the wheels clean, I mounted a stiff square fingernail scrubber. Does a decent job.

Dengue
When a bandsaw blade breaks away from the join with a straight break the most likely cause is fatigue (possibly but not likely accelerated by over tensioning). Over tensioning is not usually a problem on small bandsaws. Usually there is a problem getting ENOUGH tension. The spring in most small saws can never produce enough tension to snap a 3/4 blade unless the spring is collapsed ( see later)

A 14" bandsaw is really a small bandsaw and the blade flexes a lot going over 14" wheels. Also as the blade gets wider they also get thicker which accentuates the fatigue problem on small wheels. I think that fatigue is the most likely reason for your band to break unless there was a manufacturing fault in the band. Butt welding a blade should have no effect on the blade 120mm from the join.(have a look at the recommendations for blade to wheel size from manufacturers that make industrial blades)

Many small hobby saws advertise that they can accomodate wide bandsaw blades. However many of these claims are wildly optimistic. I have a Woodfast BS500 (19" wheels) which is supposed to handle up to 31mm(1 1/4") blades. This is ridiculous as my saw has no hope of correctly tensioning this size blade. I limit my blades to 3/4" (20mm) which is much more suitable for this size saw. Sure you can fit a wider blade and it will track etc but it will produce no better performance that a 20mm blade. 1" and up blades are really suited to industrial size saws.

A carbon steel bandsaw blade is normally correctly tensioned between 15000 and 20000 psi with a bimetal blade increasing to 25000psi. For a 3/4" x 0.035 blade tensioning to 20,000 psi requires in the order of 600+ lbs tension which most small saw tension springs can't quite manage. If you try to get this level of tension on a small saw what happens is the spring continues to compress until the coils touch and when this happens the tension in the blade rapidly increases with only a small further rotation of the tensioning handle. This is not a desirable situation. It strains the bearings/frame of the saw and the blade has no protection from shock normally provided by the tensioning spring. In this situation a broken blade is a real possibility.

I know that many people report using 1" plus blades on small saws (14") and get away with it. But it is not a desirable situation and not necessary. Blades this wide and thick are not really designed to flex over such a small radius. Modern steels help but do not eliminate the problem.

Its a little ironic that a 16-20mm blade correctly tensioned on a properly set up saw will cut just as straight as a wider blade on a poorly set up small saw.

Happy sawing
Ron

Update

Just went and measured the tension in my 3/4" Doall 3tpi blade on my Woodfast BS500. I have an iTurra Tension meter for measurement

Using the gauge in the bandsaw the 5/8' blade setting produced a measured 11000psi. I had to increase the bandsaw gauge setting to well over the scale for a 1 1/4 blade to get 20000psi in the 3/4 blade. However the real problem was that as one increased the tension towards 15000psi there was ever decreasing result such that the tension spring was very close to its collapsed length to get 20000psi.
It would be impossible to correctly tension a 1 1/4" blade on my bandsaw and a 1" would be marginal . I intend to stick to a maximum of 3/4" blades in my 19" bandsaw.
It would be interesting to measure what tension some of the smaller saws can actually achieve.
Ron

Originally Posted by ronboult

Update

Just went and measured the tension in my 3/4" Doall 3tpi blade on my Woodfast BS500. I have an iTurra Tension meter for measurement

Using the gauge in the bandsaw the 5/8' blade setting produced a measured 11000psi. I had to increase the bandsaw gauge setting to well over the scale for a 1 1/4 blade to get 20000psi in the 3/4 blade. However the real problem was that as one increased the tension towards 15000psi there was ever decreasing result such that the tension spring was very close to its collapsed length to get 20000psi.
It would be impossible to correctly tension a 1 1/4" blade on my bandsaw and a 1" would be marginal . I intend to stick to a maximum of 3/4" blades in my 19" bandsaw.
It would be interesting to measure what tension some of the smaller saws can actually achieve.
Ron

There is a school of thought that says 14" saws and under can barely tension a 3/4" blade and the 14" wheels cause blade breakage due to trying to bend the blade in a radius that is too tight. I reckon my Minimax 18" SN45 is right at the limit with an 3/4" blade and forget 1" it is just not going to happen.

Yes Chris totally agree

Can I play devil's advocate ??
If I wanted strips of Jarrah 50x2mm - I would use my table saw - Hafco contractors 12" saw with 60 tooth blade from H & F. With this saw I have cut off strips less than 2 mm when finish cutting to a required size.
This gives a very fine finish that sand well with 120 grit belt sander.
Maybe I read it wrong and you wanted 10 x 2 mm strips - I woul\d still use my table saw.
Am I missing something