If you ever wondered why it’s so hard to resaw large pieces of stock on the bandsaw – you’re about to find out.
Engineer/woodworker Matthias Wandel builds woodworking tools out of wood – the kind of tools most of us buy – so we can build stuff out of wood.
He’s written a great article with a video on his woodgears.ca website: The physics of bandsaw resawing
He uses a "sawdust board" and a wood blade to very effectively demonstrate what happens as the bandsaw blade cuts through boards.
Sawdust overload
Resawing 3" or 4" wide stock stock is faster and requires less effort than 8" stock. Much of this difference relates to how many teeth are in contact with the stock and the amount of sawdust they create in the process.
Matthias explains, as the thickness of the stock you’re resawing increases, the blade has to carry more sawdust out of the cut than the blade can handle.
"Once the space between the teeth is full, some of the sawdust gets squeezed into the kerf next to the blade, which then causes more friction. The sawdust may be forced more to one side than the other, which can lead to the blade wandering.
The solution, it would seem, is to cut slower. But as the blade gets slightly dull, the tip of each tooth becomes slightly rounded instead of a perfect point. When the tooth isn’t pushed into the wood fast enough, that round causes the tooth to just rub on the edge of the cut instead of biting into the wood. So really slow feed rates only work when the blade is very sharp."
Blade deflection and tension
A blade with fewer teeth per inch will allow more space between teeth to carry sawdust out of the cut. But as the stock gets wider, more feed pressure is required, and this can cause blade defection – which only adds to the problem.
A wider blade can help keep it from deflecting as more force is applied. Higher blade tension can also help overcome blade deflection.
Here’s Matthias’s video demonstration of the physics behind it all.
More articles from woodgears
There’s a ton of really fascinating stuff at woodgears that you won’t find elswhere. If you’re interested in bandsaws and portable sawmills here are a few more woodworking articles from Matthias Wandel’s unique perspective as an engineer.
Building a bandsaw out of wood
Testing his homemade portable bandsaw mill
A gear-cutting "showdown" between a bandsaw and CNC router
images: woodgears.ca
