Strings on Bandsawn Lumber
A discussion of why bandmills sometimes produce a stringy cut in some wood. March 26, 2009
Question
Does anyone know what the cause is or what it is called when wood strings appear as lumber is being cut with a Woodmizer bandsaw. We cut cedar and pine and almost every board has wood strings hanging on it after being sawn. Is this normal? People have suggested that it is either dull blades (even though it occurs with brand new blades also) - so could it be the set on the blades? Or cutting too fast (we have experimented with the power feed and speed doesn't seem to matter, the strings appear at any speed).
Forum Responses
(Sawing and Drying Forum)
From contributor S:
I’ve never heard of a wood string. Is there anyway you could post a photo of this?
From contributor H:
It's interesting that you bring this up as we seem to have the same thing happen. We also saw a lot of pine and cedar with a home built mill and with different makes of blades. It seems as though the blade is "tearing" the lumber just as it comes out of the wood.
Generally, it isn't much of a problem except when we cut cedar lap siding and it leaves a ragged edge exposed and we have to sort of clean it up by hand and tear off the "strings" to make it look good. Hopefully, someone will have a suggestion as to why this happens.
From contributor C:
The fibers of some woods will be stringy when cut. I have seen it on pine, not ERC, and on white and red oak. I never gave it a second thought, as rough sawing is a long way from a finished product.
From contributor T:
In see the same thing in ponderosa pine on the exit side of the board. One pass with a plane or even a gloved hand will remove them from the dried boards.
From contributor R:
Being in the woodworking industry for over 30 years, I too operate a sawmill. Here’s the rule of thumb, but not etched in stone. No matter how sharp your cutters are, which include your blades, the fibers in soft wood will tend to tear especially when there is less mass where you are cutting, (when the blade exits) on most hardwoods the fibers will shear better.
If you wanted to stop this you could put a backing board between the fences and the cant your cutting the siding or the boards from, and that will pretty much take care of that. Of course you’re going to end up with stickers depending on your cut.
From Gene Wengert, forum technical advisor:
The strings will show up on softer woods. The tooth can either cut the fiber or push it out of the way. With a softer wood, it is more likely that it will be easier to push the fibers (creating a string) than to cut it. Strings increase when the blade is dull, hook angle is too small, bite per tooth is too big or too small. Too small is likely in many mills - they need to feed a bit faster or reduce the number of teeth per inch of blade. But check the hook angle and increase it for these softer woods. (Some pine is hard, but others are soft).
From Gene Wengert, forum technical advisor:
Ooops! I should have said that we need a smaller hook angle.
From contributor F:
Thanks fellows, I've wondered about the strings as well. Contributor C put it succinctly when he said "rough sawing is a long way from the finished product." However there have been times when the boards come off the mill looking pretty darn good!
From contributor B:
Timberking recommends a larger hook angle, tooth size and set for soft logs. I don't sharpen my own bands so can't offer any firsthand experience other than what I've seen when sawing. I've seen strings from pine come back to a hardwood same band no strings. It seems logical that a higher tooth more gullet area, larger set move more sawdust less pulled fibers.
