by Alan Carruth » Thu Nov 01, 2018 1:03 pm
A few years back we had a local luthier's meeting at my shop. Somebody mentioned using a Dremel to sharpen bandsaw blades. They simply held the tool at what looked like the correct angle, and used the side of an abrasive cutoff wheel to touch the front edge of each tooth. I tried it, and it certainly got the saw sharp. The problem was that I couldn't hold the angle well enough to get the teeth to all be the same, so it made a fairly rough cut, and had a lot of drift.
As a stop gap jury rig I made up a bracket that would hold the Dremel at a good angle, and screwed it down to a small piece of plywood. A strip of wood screwed to the bottom runs in the guide slot on the saw table. I drilled and tapped a hole in a piece of Delrin, and screwed that down to the play base in line with the saw cut made when I slid the sled forward. A setscrew in the tapped hole locates off the gullet of the teeth to give a more or less uniform depth.
In use I first unplug the saw motor, and find the weld. If I can't find that I just mark the blade so I'll know when I've hit all the teeth. I run the sled in and set the setscrew so that the wheel barely touches the surface of the tooth in front. A 'dull' saw only has a tiny flat on the tooth, and you don't need to remove much material to make it sharp. I get comfortable on a tall stool and hit each tooth lightly, pulling the blade up with my right hand when the sled is retracted, and running the tool forward until the setscrew hits the bottom of the gullet. On a typical 105" resaw blade the whole process takes about twenty minutes. The blade will end up at least as sharp as new. I can get three or four sharpenings out of a blade. Usually they break, but I've had a couple where the teeth got low enough that the gullet was no longer sufficient to clear properly. You also lose set, of course.
For re-sawing I use a tall fence with an adjustable angle. I have to re-set the for the drift every time I re-saw.
One revelation I had was that you can use this method to sharpen carbide tipped blades if you get a diamond cutoff wheel. This is a real saving. Many of those blades use an alternating angle: left-center-right-center. I've had good luck simply grinding those back to straight across.
There is an issue with certain re-saw blades; the ones that alternate between 3-4 TPI: you can't set up the depth guide on the gullet. On those you'd probably need to use a depth set that guides on the un-filed teeth. This could be built into the base easily enough, and, of course, would work for saws with even tooth spacing as well. For that sort of stop you would probably want to turn the saw backwards by hand while you jointed off the tips of the teeth with a file or diamond stone to get them even.
Some folks object that band saw blades don't cost all that much, so why not just replace them? It takes me about as long to replace a resaw blade as it does to sharpen one, and even with 6-tooth blade, which takes longer to touch up, you're still out the cost of the blade. Besides, it just goes against the grain to throw out something that can be re-used.
The original plan was to try out the idea with a quick and dirty setup, and then go to the Delux version, with easily adjustable angles and so on. The jury-rig worked so well I'm still using it, more than a decade later. I could get a picture and post it, if you'd like, but the idea is simple enough that I hope the description suffices.