Troubleshooting Grain Raise in Hemlock
Grain raise can be addressed by tweaking planer operations. January 27, 2007
Question
I am working with more and more Eastern hemlock and producing flooring and other millwork. The problem arises after the fact when we see grain raise that was not evident before the wood went through the moulder. I believe that I once read that part of the problem may be in my milling process. I am very aware of the problem with shake in hemlock and can generally pick out 95% of it after kiln drying so that is not the problem. It arises in face grain, generally when the good side of the work would be "bark side up," as they say. Am I causing the problem with my moulder, or is it something else?
Forum Responses
(Sawing and Drying Forum)
From contributor R:
Bark side up is a great way to start. 20 degree hook angle on the cutterhead would help. 25 degree back grind on the knife with a micro 20 degree finish grind. Try that and see what happens. I hope that solves the problem.
From Professor Gene Wengert, forum technical advisor:
Grain raising occurs when the more dense wood within a ring is pushed down into the softer wood. Why is it pushed down? Because it is too hard to cut the wood fibers...which means dull knives (carbide is worse), small depth of cut, slow feed, low MCs. Usually, it is not just one area needing attention, but two working together. Note that if you plane both sides, this defect will show up only on one side. Further, if it shows up on one side and you were to reverse the piece and re-plane it, it will not show up on the same side. So, if possible, plane the good side so that you are planing the tip or peak of the cathedral or "vee" first. It will not show up with q-sawn, but will be worst with perfectly flatsawn.
From contributor J:
Splinters raising out of the grain is a characteristic of hemlock. Early on this characteristic was the reason for the robust hemlock market, as the rats and mice could not chew through the granaries and corn cribs made of hemlock boards.
