Troubleshooting Planer Setup and Tearout
Tips on setting up a planer to avoid tearout. January 2, 2012
Question
I am getting a lot of surface tearout/chipping with my planer. The knives are fairly sharp. Could it be that the chip breaker isn't adjusted properly? What distance should the chipbreaker be from the knife, and at what pressure should it be set?
Forum Responses
(Solid Wood Machining Forum)
From contributor M:
If you can get a hold of a manual for your planer it should specify tolerances for the height of both the in-feed and out-feed rollers, as well as the chip breaker. It is hard to give any specific numbers without knowledge of the machine in question.
From contributor W:
Improper setting off-feed rollers and chip breaker could cause chatter and the resulting tear-out as well. As the previous post said you should always go for factory specs when setting things.
When I used to set my old 24" SCM planer, I would use two pieces of very straight maple 2x1 s4s (on edge)and lay them down like tracks underneath the machine. I would then lower the planer down very slowly until the planer knives would make contact with the s4s. I would be rocking the knives a little from the top of the machine to make sure I contact the wood at the apex of the cut. Then I would unbolt the hinge of the pressure shoe and set it exactly even with the knives.
Then I would start by setting in-feed and out-feed rollers even to the s4s as well. After doing this I would lower the out-feed rollers about (1/16") by turning the setting nuts 3/4 of a turn of the bolt each side. I would keep the in-feed rollers even to the knives.
In general though, the chip breaker will usually only set up and down on a planer with the in-feed rollers, and not in or out. It should be set to the same height as the in-feed rollers as well. (It might be different on your machine though). Also you want to make sure your knives are set at the proper height in the head (about 1/8-3/16) above drum). If you get sticky feeding then maybe adjust your rear feed rollers up 1/32 on each side, and use a little Waxlit on the table surface. Add good suction and you should be cutting pretty smooth.
From contributor H:
I set my knives at .07 outside of the arc of the cutter head. My Powermatic book says .125 but that left me with a crappy finish. After setting the knives I then set the chip breaker, pressure shoe and the feed rollers to specifications, they are based on the planed surface height. I used a dial indicator for this and also for setting the knives and have never changed any of the adjustments since I set it up. I always put the knives back at the same height in relation to the diameter of the cutting head.
Dull knives will make a difference, sometimes I have changed knives several times a day depending on the amount and wood species I am planing. Really sharp steel knives are a joy to use. The first thing I would do is clean the machine, replace the knives, and reset everything.
From contributor Y:
Just a thought, but are you sure it's tearout? I have a problem with my General 15" . Lots of little tearouts on pine but on closer inspection they turned out to be depressions caused by chips being thrown around the feed roller and being pressed into the wood. A hit with a steam iron caused them to pop back up. I first thought it was the wrong angle ground on the re-sharpened blades but now I'm thinking it's a problem with the suction system not clearing chips properly.
From the original questioner:
Yes that's a problem with your dust extraction. The chips get carried around by the knives and pressed into the surface. Improve the suction and it will disappear.
From contributor B:
Steve, did this tear out/chipping just start? If so, perhaps the stock you are running is the problem. Does it change when you switch directions? Do all boards chip? I don't think the chip breaker or the pressure is causing the chipping. What feed rate are you using?
From contributor L:
First as mentioned, what planer is it? This will help determine what type of chip breaker is in it. In general, it has been my experience that Contributor H is on the right track. The distance that the knife protrudes past the diameter of the head is critical. The farther the knife extends, the less the hook angle of the blade. Depending on the species this can be extremely important. This setting also varies based on the backgrind of the knife. Too sharp of a grind may work on some species and not another. I am referring to the sharpness actual angle of the knife grind and not the cutting edge of the knife.
