Cracks in bandsaw blades

      Causes of small cracks in blades, and the blue stains that appears on oak after sawing. October 15, 2001

What causes blades to develop small cracks in them? We use a Woodmizer and have noticed small cracks in the blade before they break (after about 900 bd ft of sawing). We are cutting northern red oak and also notice blue stain on the face of the board after cutting. These are new blades, not re-sharpened ones. Are these related problems?

Forum Responses
The small cracks develop from the stress the blade is under. The way to help this is to pull off the blade before it gets dull and re-sharpen, grinding out the gullet. That gets rid of the cracks, in theory. We usually get about 3 to 7 sharpenings on a Woodmizer blade, and I suspect that if I ground deeper, and spent more time with blade management, I could do a bit better. I think if you are cutting 900 ft before pulling a blade, it is probably pushing it a bit. Woodmizer blades seem to be more prone to cracking and breaking than other blades, such as Timberwolf, but they stay sharper longer, and we get at least as many board feet out of a Woodmizer as a Timberwolf. Woodmizer is also not as flexible, and I suspect that contributes to the problem.

I agree.

Why don't you start pulling the blade at 400 feet and dressing it on your sharpener? If that seems too frequent, go to 500 ft. My opinion is that 600 feet is about maximum use before sharpening, although some may get more. It's more economical to pull the blade before the tips are dull.

Cracks in the gullet can also be caused by driving the blade too hard even when it is sharp. Gullet cracks are caused by uneven grinding in the gullet and/or a sharp curve at the base of the tooth. Frequent sharpening won't do much good if done improperly.

The blue stain may be caused by contact of the iron in the blade with the tannins in the oak. This usually doesn't occur unless you stop the blade in the cut. Iron will cause a blue black stain on oak and also oak, as well as many other hardwoods, is caustic enough to corrode the metal parts on your mill. When cutting oak you will avoid some replacement maintenance by keeping it clean.

Also watch the tension of your blade. If it falls off during the cut, run water and pine oil mix to cool it so that the pressure stays the same. Also, if the sun shines on your valve, it will heat up and cause the pressure to build up. I keep mine about 2100 lbs. I average about 800 bd ft a blade in red and white oak, so I think that heating of the blade by forcing it too fast is the cause. So cool it or slow down and watch your pressures.

The blue stain is from the blade and will come off with a sanding or a trip through the planer.

Increase your set just a bit and make sure your feed rate is adequate. Blue stain in oak may indicate that you're running the body against the cut. Try a lennox C at 3/4 pitch in the oak--I think you will like the results.

You could also clean the oil off the blade as it comes out of the box, when it is new, or back from re-sharp. I've had a stain from a new or re-sharpened blade. It could be the oil or just some small burrs or filings on the blade from when it was made. The blue stain could be the reaction of metal touching the oak. Most oaks react to metal, making stains. The body of the blade shouldn't touch the board or the log, just the teeth should. When we were taught how to use our own sharpener they told us to take a piece of hardwood and rub it along the blade to remove the burr caused by grinding it. This burr can effect your setter when attempting to set it. I believe that this burr could also be on new blades, and could be what's causing your stain.

I find the black oak here stains from a reaction to the minerals found in the local water (well water). It's light and sands out or planes out if you get to it soon.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor F:
I found that the staining can be removed using a very diluted phosphonic acid solution. It is a chemical used in the redwood lumber industry to control the tannic acid streaking that is common in redwood and western red cedar. You can contact Contechem, Inc. in Portland, Oregon. I had a shipment of Western red cedar doors come in from Canada that had a lot of tannic acid streaking. I about panicked! Then I remembered that I had the phosphonic acid solution and sprayed some on the doors. The streaking disappeared in front of my eyes. It's cheap and does the trick. We use it on our log homes because we found that just the dust that accumulates during construction contains enough iron to cause a slight gray stain. A quick spary with about a 1-2% solution of the acid brings it right back to life. The MSDS says that it has almost no negatives to humans or the environment.

Comment from contributor L:
I had problems with blade cracks and breaking for years on my bandmill and after having a technician from Starrett come out and check the blade tension on my machine to be sure it was within spec, I started to look for other possibilities.

One day when doing a bearing change on the wheels, my son was helping me with the alignment of the wheels to be sure that they were on the the same plane. He noticed that after lining up the wheels and putting the blade back on and tensioning it, the wheels were no longer on the same plane. The put more tension on one edge than the other, causing stress cracks and eventually breakage.

We realigned the wheels while under tension and I have lost one blade in the last 6 months, and that is with using my old blades. If you are having trouble, this is worth looking into, as blade tension puts tremendous strain on the mill and can change the shape of the frame. Blades are not meant to bend laterally.

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