Cants pulling away from line bar

      Problems with cants that don't stay properly set up during milling. August 1, 2001

Question
We are having problems with our boards and cants pulling away from the line bar when running them heart-side down and pulling towards the line bar when running sap-side down. The wood pulls away on the in-feed rolls before it is in the machine and in the machine, even with the press rolls down. We can counteract this on the straightedge pieces with the crowd roll, but not on the double live edge pieces. The cants and boards are coming from a 9-foot band saw with a saw running a frost pick to prevent washboard.

The pullout seems to worsen on different species of wood. About a 6 inch pullout on spruce over 20 feet, and only 4 inches on yellow cedar over 20 feet.

We have replaced and aligned all the rolls and bearings on the edger to no avail. Could the frost pick on the 9 foot headrig be causing some sort of fiber tear to cause this pullout?

12 inch 5 saw bull edger,7 inch 3 saw pony edger.

Forum Responses
The first thing to do is to check the thickness of the lumber to make sure that one edge is not thicker than the other--use 0.001" measurement. Measure three spots on each edge.

Next, if you have lumber that is partially quartersawn, you need to change the sawing pattern--use 180 degree rotation from the opening face to the next face. The problem is that there is stress in the tree, so when you edge the lumber, you unbalance the stress. Take a piece that has given you trouble and see if the annual rings are perfectly centered, edge to edge. Also, measure the straightness of a piece, run it through with only one saw in the piece. Then see if the edging strip and the main piece will fit together or if there is a gap. A gap means that you have significant stress in the tree. This test would be best if you were to split an 8" piece into two 4" pieces.

Finally, take a piece that you think will cause problems and cut a skinny strip off of the edge closest to the line bar. Which way does the piece move? Then take the same piece and cut a skinny piece off of the far edge (the opposite edge), away from the line bar. Do you get the same movement both times?

Gene Wengert, forum technical advisor



From the original questioner:
We have done measurements on hundreds of pieces and the variance in sawing from top to bottom from the headrig is very minimal. Maybe .005 inches over 26 inches of width or no real variance at all. Tree quality doesn't appear to be a factor either, as all pieces run away equally. The strangest thing is that the pieces run away from the linebar heart-side down even before they get into the machine. And with sap-side down, they hug the line bar tight from the second you drop it.


To eliminate the lumber surface factors--cup, tension, etc., try running through some pieces that have been planed smooth.

Gene Wengert, forum technical advisor



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