Holding a Cant Down on the Bandmill
A bandmill owner gets help troubleshooting the situation when a cant seems to rise off the sawmill bed while sawing the last few boards. April 18, 2015
Question (WOODWEB Member) :
I am new to bandsaw milling and have a basic question. When I get down to the last couple of boards in a cant I find that the blade on my mill lifts the cant off the bed slightly resulting in uneven cuts. How do people deal with holding down the cant on the bed when it gets lighter and thinner?
Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
Is this a horizontal band? Is the cant only held down by gravity? What brand of mill?
From the original questioner:
Yes, it's a horizontal, manual - 25 horse Turner Mill. Just gravity and the dogs hold the cant to the bed.
From Gene Wengert, forum technical advisor:
So, why aren't the dogs holding the cant down? Are they perhaps dull so they do not penetrate much?
From Gene Wengert, forum technical advisor:
I should have added that most dogs are designed with a bevel so the deeper they go, the tighter they hold the cant to the bed. Perhaps somehow the dogs got reversed?
From contributor Y:
There are a couple of things you can look at. The most likely is tension in the log. As you mill, you relieve the tension and the cant tries to move. Watch the boards as you cut. If they bend up behind the saw blade you have found the probable cause. When you see this happen, rotate the cant 180 degrees and cut from the other side until you see a board curl. On a log with a lot of stress you may need to rotate after every cut. Try cutting the last board 1/2" thicker than you want it and then turn it over. If it rests evenly on the crossbunks and the last cut gives you a straight board you can be pretty sure you were dealing with stress. "Logs" from branches are the worst for stress, but leaning trees can also have a log of stress (look for off-center growth rings). Sometimes it is there for no apparent reason.
Second, how is the blade cutting? Do you have trouble getting it to cut straight? If the blade pops up as it exits the cut of a full size cant, the blade is trying to move down into the cut. When you get to the last few boards, the cant is light enough that the blade can lift it. This means a problem with the blade (possibly set of the teeth), alignment of the blade guides or the blade not tracking correctly on the band wheels. A fresh blade will help narrow the diagnosis.
From Gene Wengert, forum technical advisor:
I like Contributor Y's answers, especially the first one. Regarding the second answer, I do wonder if a properly secured cant can be lifted by the narrow band blade when the dogs and gravity are resisting.
From the original questioner:
Excellent advice on both accounts. Bill Turner is sending me another low profile dog to help secure the cant and I will definitely observe the stresses in the log and try flipping the cant if it seems necessary. He also thought that log stress might be a factor. I don't think that it is the blade, which seems to be tracking well and cutting straight until the last couple of boards. I run a vertical bandsaw in my shop and am used to setting the guides, so I think that they are okay.
From contributor N:
Most bandsaws only have one dog and would need three to hold a cant with stress down. With a cant that is bowing up on the ends and turning it over keeping the ends on a bunk will help. Have a helper hold the center down when clamping.
From Contributor O:
I like what Contributor N says here. We have even dogs with a tooth, close at every bunk. The bunks have a fixed tooth opposite the dog side, all teeth about 0.7" higher than the bunk surface. The dogs teeth pinch and pull down in the same moment. That means it is safe and easy to resaw boards or cut the last board from the cant. Be careful to support the end of the cant or board, it is also very important. In most cases you have the ends of the cant hanging over the bunks. It is, in my opinion, most important to support the further end. Why: in the end where the saw enters the board is still stiff and the feed force has less impact. If there is a hangover in the further end, the board is divided in two parts and is much weaker to up and down forces. The feed force will bend the end down and after that the blade has past the last bunk. The result is a thinner end in the board just cut and a thicker end of the remaining board on the mill.
From Contributor B:
If the log is supported by a bunk at its far end I would make and use a giant "C" clamp to bring it back into line so the cut is an even thickness.
From the original questioner:
I'm still struggling with this. I find that I get some lift on both ends. I wonder if I should spend some time adjusting the guides.
From contributor H:
If it’s cutting ok but for the last board or two I would guess it is the wood that is bowing.
From contributor Y:
Leave the guides alone! If it is cutting straight, except for the last few boards, then you are dealing with stress in the wood. What species are you working with? I've found, for example, that hackberry (in the elm family) goes every way but straight when I cut it. Trees with a lean to them also have stress (look for off-center growth rings). Check the Knowledge Base, and enter "stress" as a search word. The thread below came up, which may be helpful. There are others, too.
Sawing An Old Elm Tree
From Contributor L:
If there's no tension in the cant I leave a few boards on it and don't use the dogs. The weight of a couple boards is plenty to hold the cant in place. Flipping the cant each cut sometimes releases the tension so the last few boards stay straight.
