What I Screwed Up This Week – November 28, 2010


Well, I hope everyone in the States had a very happy Thanksgiving.  As usual, I ate too much and had to work the weekend.  However, I still managed to get in some shop time.  That, of course, leads us to this edition of What I Screwed Up This Week.  This one actually happened a few days ago, but I just now worked it in to the lineup.  It actually relates to stock preparation that I did for the frame of the Wing Chun dummy.

The Problem:

As I was ripping 2×10 stock into 4” widths for the frame components, reaction wood caused one of the 8’ pieces to bow inwards.  This is always a prime cause of kickback, but fortunately, my SawStop has a very good riving knife, so I was in no immediate danger.

The Solution:

Wing Chun Dummy - Prepping the Stand Stock 1Interestingly, the piece was only bowing on the left-hand side, away from the fence.  The fence-side part of the wood remained perfectly straight.  Such things can occur as a result of varying stresses on different sides of the log caused by unequal growth.  Due to the fact that I still had a solid fence reference, I decided to continue with the cut, but remained well out of the way.  The cut went just fine until the last inch, when the built-up stress of the curving piece pressing against the far end straight piece caused the two parts to separate rather violently, sending the left-hand piece almost a foot across the table.  You can see the result in the photo to the left.

Lesson Learned:

Always be alert for reaction wood.  A piece such as the one above that spans the pith of the tree is a prime candidate for this.  If you notice bowing in a piece as you cut, stop immediately and asses the situation.  If you don’t have a riving knife, DO NOT CONTINUE THE CUT.  Even if you have one, don’t continue if the wood is warping away from the fence.  In retrospect, I underestimated the force of the bowing action of the wood, and had an unexpected occurrence at the end.  I probably should not have continued the cut either.  Remember that if wood shows signs of movement, it’s not going to stop until the energy is expended.  Also, never forget that tablesaws don’t have a very forgiving nature.  When in doubt, shut it down.

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