Wavy surfaces in planed lumber
December 1, 2011 | 6:00 pm 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.

 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.



 Q. We are using epoxy adhesive and have a few questions. How can we speed up curing? The instructions are clear that we cannot add more catalyst or hardener. Also, we tested one joint the next day and noted it failed rather easily and we saw that the failed joint where the adhesive was appeared grainy and not smooth. What is this? Finally, how can we clean up cured epoxy?

 A. You can speed up curing by heating the wood and surrounding air. Roughly 17 degrees F hotter will cure twice as fast. By the same token, 17 degrees cooler will cure half as fast.

 The grainy appearance of a broken joint is typical of using too much pressure with epoxy. When there is too much pressure the epoxy is squeezed out of the joint and the chemical activity cannot occur. (I believe that most bad experiences with epoxy result from using too much pressure.)

 Also, you should be aware that although the epoxy cures in a few minutes, total cure and maximum strength will not occur for 24 hours. You must wait for full strength to develop before testing.

 As far as clean up, I contact West Systems and asked them, as I did not know the answer. They stated that due to the high chemical resistance of cured epoxy, removal must be done with an epoxy-type paint stripper containing methylene chloride. Uncured epoxy resins and hardeners can be cleaned up with ketones, alcohols, or lacquer thinner. White vinegar will clean up unmixed resin components.



 Q. We have changed lumber suppliers and when our new supplier measures the board footage, he puts several pieces together tightly in a single layer that is about 36 inches wide. He measures the actual width. With a layer that is 36 inches x 10 feet, he then calculates 30 BF of 4/4. Is this OK? It certainly is easier.

 A. This is called a block tally. It is legitimate and accurate. All pieces must be the same thickness; and preferably all pieces are the same length as well. When all the pieces in a layer are not the same length, an estimate of the short pieces is made and the footage reduced proportionately.

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About the author
Gene Wengert

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.