Equipment or Design Failure?

I’ve recently made a band saw circle-cutting jig. It’s a length of board marked out from 1″ to 42″ and intended to cut various diameter circles. To cut a 3″ circle, I place dowel (or pin) at the 1-1/2″ mark with the stock against the band saw blade. First cut worked great, but subsequent attempts pushed the 3/8″ saw blade “out” of track. Changing to new blade got the same result. What am I doing wrong? Is it blade tension? Jig design?

Michael Dresdner: Hard to say without seeing it, and strange that it worked the first time, but not subsequent times. Make certain that the circle jig is positioned correctly relative to the blade. A radius drawn from the center to the edge should strike exactly at 90 degrees just in front of the cutting edge of the blade. If the radius hits either in front or behind the cutting edge, it can cause the blade to drift. Reposition the jig so that the radius forms a 90 degree angle to the blade, and ends just in front of the teeth.

Lee Grindinger: I can think of a couple of reasons. Whenever a blade wanders during a cut it’s either a bad blade or bad set up. Be certain that the blade is properly supported by the guides and thrust bearings. To tension your blade tighten the blade until you get a sweet bass musical note. The tension markers used in smaller saws are not reliable. Are your blades stored properly? Could they be damaged during storage? A few damaged teeth will cause a blade to wander. Also, band saw blades very often do not track parallel with their tables. Find the angle your blade tracks by sawing straight into a board and placing the back of the blade precisely in the center of the kerf. Strike a line on the table parallel with this line and set your circle cutting jig perpendicular to this line.

Rob Johnstone: It would be hard to know for sure as I cannot see what is happening. If it worked well once, I would guess it is not the jig design. (Although if you would like a good one, the February 2003 issue of Woodworker’s Journal has a great design for several band saw jigs, including a nice circle-cutting jig by band saw guru Mark Duginske.) My best guess is that your saw is not tuned up well. Not simply the blade tension (which is important), but the blade guides and blocks, etc. Duginske’s band saw book would be a good place to learn how to tune your saw. I’ll bet it will have you singing a different tune in no time.

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