Bandmill Blade Breakage at the Weld
A discussion of bandmill blades, welding, and what might cause blades to frequently break at the weld. August 29, 2006
Question
We have been having a lot of problems with bandsaw blades breaking on the weld joint. We order in 6 blades, get them on Monday and by Tuesday afternoon, 4 will have broken on the welds. The other 2 will run until they have been ground down and will not fit the machine. We send the bands back and the company will reweld them for us, but again when they return, we get about 50% breakage rate. Part of the problem is when they break, it damages the teeth and kinks the saws. Is there a way to arc weld the bands and then temper them myself?
Forum Responses
(Sawing and Drying Forum)
From contributor R:
No, it takes a special welder to weld bland blades. What kind of blades are you using?
From contributor T:
Honestly, if you are having that much band blade breakage, don't you think you should look at something else? Maybe you have too much tension. Maybe you should look for a different supplier. Maybe you should slow down your feed rate. If I was breaking blades that often, I'd certainly start looking at myself before I went and pointed fingers at the weld or the supplier. Have you backed off the tension to see what would happen?
From contributor I:
80% of my bands break elsewhere than the weld. I had one new band that I put on my mill that was misaligned and welded. It wobbled as it went through the guides. I ran it anyway and within 20 minutes of cutting, snap - right where it was welded. Wheel diameter might also be a factor.
From contributor A:
Out of all the blades that I have run over all these years, none have broken at the welds. That tells me you need to buy blades from someone that really knows how to weld them and distress them correctly. Call Cooks Saw and Machine and get the best blades for the cheapest price on the market. These people ship out 5-600 blades per day. They really know what they are doing. No, I do not work for them, but I get most all my blades from them that I have to buy. I have received close to 100 free blades from lots of manufacturers over the years. Tested them and gave them feedback.
From the original questioner:
Thank you for all of your responses. I have tried lowering tension, raising tension, slow feed speed and faster feed speed, but they still break on the weld. I thought that if the machine was the problem, they would break anywhere on the band, not just on the weld. The ones that don't break run good. The only breaks I get are in the gullet and that happens when my filer doesn't sharpen them correctly. I check the bands when I get them and on some of them, the weld is ground down so much you can see the joint line. The problem with changing suppliers is that I'm in Costa Rica and the only supplier is in San Jose. I have talked with him but he says our machine must be the problem.
From contributor I:
I agree that welding bands requires special equipment, however, people in metalworking do it all the time. In fact, many vertical metal bandsaws have a band welder built into the saw. (It is common to cut the blade and re-weld it so that an interior cut can be made.) For example, check out the Grizzly saws. These welders are also available separately. I know it takes a special knack to get it right, but with the apparent problems you are having, it may be worth investing in the equipment and developing the skill to do it yourself.
From contributor T:
You don't think that you are getting the runaround because you live in CR, do you? Also, I'd find another supplier willing to ship or find someone here that can ship them there for you. There has to be another supplier who can get you blades.
From contributor B:
If your blades are breaking prematurely at the weld, you have a bad weld. If your blades are no more than an inch in width, you might get an inexpensive zap welder to do the job yourself. If you are using bands wider than that, be prepared to spend a wallet full, maybe even take out a loan.
From contributor S:
You could try joining by brazing. An elderly Portuguese ex-sawmiller I worked with joined 1 1/2” blades by brazing and they never broke on the join. He folded the blade like a hair pin or clip so that the two ends were together, with the lower end protruding about 1/2” further than the top end of the blade, and clamped them together. He would then file them so that they were tapered, ending up with the lower edge of the ends tapering to zero thickness. When the blade ends are placed together to make a band, the tapers overlap and the thickness should be the same as the rest of the blade. He would place some thin brass shims between the tapers with brazing flux or borax on both sides of the shim and wire then together. He then heated them in a charcoal forge until the shim melted, after which he smothered the joint in wood ash to allow the join to cool slowly. All that was required after that was to clean up any irregularities on the join with a flat file. I personally have silver brazed small hobby machine blades with a gas torch using the above joining method and it worked well for me.
From contributor D:
Have you checked your guides to see that the back of the blade is being supported while cutting? A tensioned blade should be within 0.020 inches of the flange on your roller guides when the saw is turned by hand. If your saw shop does not have a big enough blade welder, the weld may not be completely formed. It takes a 3 phase blade welder to do a good job on the 1 1/2 x 0.050 blades.
From contributor J:
The Cook's website says if your wheels are not fairly true, your machine will eat blades. Have you checked your machine to see how far off your wheels are? You should be able to set up a dial indicator with magnetic base and turn the wheel to see what is happening.
From contributor O:
I think I would try blades from other suppliers, even if the shipping is higher to CR. I bet there is another issue, since you said tension changes don't change anything. I wonder if your guides are true with the band wheels? Any little twist would place a load on the blade weld that would fracture it.
From contributor H:
It sounds like the welded joint has not been tempered properly after welding. When the saw is welded, it air cools rapidly and is very hard (brittle) and will break easily. It should then be cleaned to show the bright steel and then heated at a low setting on the welder until it turns blue (like a clock spring). This slightly softens it and makes it tougher. The process can be repeated using a gas torch, heating gently and watching the oxide colours on the steel, yellow turning to brown, etc. When the steel turns blue, stop heating, or better still, quench it with a wet cloth. This will not affect any prior heat treatment other than to correct any fault due to incorrect tempering.
