A case for “case hardening”?

July 21, 20143 Comments

Over the weekend I was resawing with my bandsaw, for the project video I’ll release later this week. All was going well until I noticed the blade started to make an unusual sound. The wood felt as if it had gotten stuck, then ALL OF A SUDDEN…BAM!!! the blade came off the wheels and it all came to an end.

on and off switch for band saw

In a moment I went from happy woodworker, to a guy who was hurriedly hitting the stop button followed by considering whether he had to go change his pants before trying to figure out went wrong. The good news is I was all clean, no mess!

The bad news is that my blade was wedged in the kerf of the 5/4 Padauk I was resawing. At this point my only option was to unplug the bandsaw, and remove the blade/wood from the machine so I could attempt to separate them. After about 30 minutes, the two were apart and I was able to resaw the remaining 4″ of length using a rip-style panel saw.

As I returned to the bandsaw I started asking myself “what went wrong, how did this happen?” “Was it my technique, the wood, or the machine itself?”

Considering how deeply the blade was wedged in the wood, and the fact the kerf was completely closed around it tells me more than likely I was dealing with a case of case hardening or at the least some reaction wood.

In fact, I should have noticed how tightly the kerf had closed on itself after only a few inches of resawing. More than likely it was the combination of the pinching wood and my pulling back slightly to readjust the cut that pulled the blade off the wheels.

Next time I’ll pay closer attention and either wedge something in the trailing kerf to keep it open for the remainder of the cut, or I’ll just stop the process entirely and consider whether I want to continue using the stock or try something else.

In case you’re not familiar with either here’s a simple definition for you:
Case hardeningA term applied to dry lumber that has residual compressive stresses, it can cause planks to unexpectedly bind on a power saw blade during ripping because once the blade cuts a kerf, the open kerf area will close in itself.

Reaction woodWood that has different characteristics than normal wood because it is formed a process in which trees bend and grow in abnormal ways due to external stresses. Reaction wood is not JUST a response to gravity; it also occurs when branches are weighed down by snow for long periods and it can occur in trees that are in an area that has strong prevailing winds and have to brace themselves against it.

case hardened wood

image courtesy of Richard Jones Furniture

Regardless of whether it was case hardening or reaction wood, the end result was the same, a momentary scary situation that turned out with a happy ending…this time.

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Comments (3)

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  1. Matt,
    This exact same thing just happened to me today on the table saw, but I didn’t need to check my pants. I was ripping some four quarter when I started to get a little resistance, I slowed the feed rate but it didn’t help and I tripped the breaker. It took me about 10 minutes to free the blade from the wood; it was clamped on there like a vise, just like a Sawstop. With a little apprehension I flipped the board and it went through like butter now that all that stored energy was released.

    mg

    • Matt says:

      I remember the first time I had this experience on a tablesaw. It took me several minutes also to wedge it off the blade, but what scared me most was the loud “BANG” from when the tension in the wood was released.

      I thought a gun was fired in my shop LOL!

  2. John Fitz says:

    Thankfully I’ve never experienced the “BANG” or “CRACK” phenomena that others have, but I’ve had a nice easy straight rip create a banana-looking piece as the wood bent uncontrollably after being cut. This is where a good splitter or riving knife on the TS can help. I am starting to wonder if some sort of splitter on the bandsaw would be a good thing during resawing….

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