Preventing Board from Crowning When Ripped
Boards sometimes crown when ripped, as fiber tension is released. There's no easy fix. June 24, 2007
I am cutting 16' Douglas fir 2"X6" lengthwise from corner to corner, creating 16' wedges. After (during) cut, they are crowning more than I would like. Is there any way to prevent crowning or reduce it? Any tips would be great. Not sure of the MC of wood, but it has been in the shop for a few weeks. If I make 2 3/4" deep cuts, would that reduce it?
(Architectural Woodworking Forum)
From contributor O:
It sounds like you're dealing with stresses that are released when the two parts are freed from each other, and my guess is there's not much you can do about it in the shop. Certainly there's no magic way of cutting them that will prevent the problem. If you need them to be straight, particularly over such a long length, you need to cut each wedge oversize, let it stabilize a bit, and then trim it to its final dimensions.
From contributor D:
That's what I thought. I was thinking about making a cut 3/4" deep, letting the wood sit, and then making my final cut a few days later. I don't know if it would matter - just messing around.
From contributor O:
Gene would be able to give a more lucid explanation, but my understanding is that case hardening can only be addressed by a conditioning process in the kiln. That said, I'd expect some distortion over a 16' length no matter how carefully dried the wood was to start with.
From Professor Gene Wengert, forum technical advisor:
Contributor J is correct. There is no cure other than serious stress relief process in the kiln (called conditioning).
From contributor J:
This is probably an obvious option to most, but I'll toss it in anyway. If straightness of these wedges is critical and cost of labor and material is covered, go to a wider stock like 2x8's and straighten the crowns after splitting out the two parts. Use a straight line ripsaw, long bed jointer, or snapped chalk lines and a power plane or circular saw.
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