Troubleshooting Sinusoidal Waves in Planed Lumber
From contributor J:
I had that happen recently with antique heart pine. It was flat sawn and the waves ran along the curvature of the grain. We face planed it first on the jointer, then planed the other side on the planer. We never got the waves out on the planer but got most of it out on the wide belt. The only reason I could come up with was the varying density/hardness between the wood in the individual areas of grain. I normally don't have to use a dictionary in my discussions about planers.
From the original questioner:
Thanks for your responses. I think I found the source of most of the problem. We had recently replaced (actually, I machined new ones) the support brackets for the infeed and outfeed rollers and the guy that reassembled the planer didn't compress the springs enough. After tightening them most of the problem went away.
Contributor J, you're right about the strategies that need to be employed when planing rough lumber. Contributor C, I have noticed that the grain direction matters too, especially on hardwoods like jatoba. So, there are many factors affecting how wood will plane: machine adjustment, wood properties and planing strategies.
From contributor L:
It may have nothing to do with your machine. If it's been improperly dried or case hardened, or not kiln dried, especially more dense woods, it can bow as you described and more. If your machine is set improperly, it should be doing about the same thing to each board regardless of species. I've had this happen several times over the years from red oak to South American lacewood. I bought a very good moisture meter. In each case the lumber dealer confirmed my findings and took the wood back for full credit.
From Gene Wengert, forum technical advisor:
Casehardening refers to a condition of stress in the wood. It cannot be measured with a moisture meter, but requires a piece to be cut into a prong, similar to a clothes pin. Casehardening will cause a piece to warp full length immediately when machining it. It causes no other problems.
Oftentimes the waves can be seen when a bed plate is worn. As the center wears most, this waviness is seen with narrow pieces fed down the center of the machine. The pressure bar can also be misset or worn and cause this same thing. Essentially, the wood is not being held tightly to the bed plate.
Heavy pressure (from feed rolls, too much heel on a knife, dull knife) with a wood that has high density differences within a growth ring (like some pines) can also cause this to happen, as the softer wood is compressed. The compressed wood will expand or springback after a short while. This springback is accentuated if moisture is present (water-based finishes, for example).
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