Why does my planer make wavy surfaces?
By Gene Wengert
January 30, 2013 | 9:00 am CST
Q. When I plane lumber, I am getting a significant wavy surface which takes a lot of sanding to get smooth. I know that planers do make a wavy surface, but this one seems a bit more wavy with longer waves. Does this make sense and can you tell me what is causing this? We also are seeing some chatter with narrow pieces.
A. For waves, my first guess is that you have one knife that is protruding further out of the head than the other knives. So, the surface you are seeing is basically a one-knife surface.


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 I wonder if you checked to see if the head was balanced. Even though there is a lot of metal in a head, sometimes unbalance will cause the head to bend slightly and create, when spinning, the marks you see. When that happens, one knife is doing more work than the others. Of course, the unbalance also causes stress and wear on the bearings.
 Regarding the idea that one knife is projecting more than the other, this can be determined easily by measuring the distance between each ridge. Compare the actual measurement with the calculated distance is if each knife is working equally.
 This calculated distance is:
 D = (12 * F) / (T * N)
 where D = calculated distance between ridges in inches
 F = feed speed in feet per minute (you can measure this)
 T = number of knives per head
 N = head speed in rpm (not the motor speed unless it is directly connected)
 R = the radius (1/2 the diameter) of the head including the projection distance of the knives
 (The 12 in the formula is to convert the feed speed into inches per minute.)
One way to obtain equal projection for all the knives is to joint the knives after they are installed. Unfortunately, jointing creates a flat spot on the edge of the knife (called the land); the net result is that the knife angles are changed and so the knives, if the land is large, pound the wood creating an inferior finish. This land must not be over 1/32-inch wide.
 If jointing does not fix the problem, then we likely have a bearing problem. Usually fixing the bearing before it gets really noisy is best. A worn, heated bearing can result in additional damage to the machine.
 For chatter, if you see problems when planing narrow pieces, I suspect that the flat bed plate is worn in the middle. Wide pieces are held firmly by the edges of the bed plate, but the wear in the middle means narrow pieces are free to move up and down a little bit. If you feed a narrow piece to the left or right edge, will it be OK? If so, that confirms my diagnosis. You could also have a pressure bar that is worn or chip breakers that are not set correctly.
 Overall, given the difficulties you are having, it might be time to call a qualified technician to overhaul the machine. It is true with planers that “a stitch in time saves nine.” Either overhaul it now at a reasonable price, or plan to do more sanding to get the excellent surface you require and set money aside for a catastrophic planer failure and repair bill in the future.


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