|Okay, I get it, I'm not the sharpest stick in the woodshop. I was making this ridiculously simple chair and we needed to round out some corners. Toby, who was working with me, took a brand new blade and popped it into a jigsaw and I cut away. I tried to turn the corner as I powered through the material but I cut too wide. And then to compound the error I did it again. |
The reason is that I'm stupid. The right way to cut a tight curve is use a narrow blade. A wider blade won't work even if you try to cut slowly. A saw can cut a curve because if you twist the blade in the cut it will turn the amount possible given the width of the blade and the width of the actual kerf of the saw cut (fig. 2). The wider the blade the less of an angle you can twist and that's the limiting factor. That's why our bow saw blades are only 1/8" wide - it's so you can turn on a dime. Wider blades are better for tracking straight.
We got the idea for 1/8" wide bow saw blades for our turning saw when we saw the blades on Duncan Phyfe's turning saw. He used 1/4" material - but for the working length of the saw blade - the blade was ground narrower to maybe 3/16".
So, if you you want to cut a curve, don't do what I did - get a narrow blade - hand or power. Otherwise you need another strategy.
Another strategy that works is to cut a series of straight saw cuts perpendicular to the final curve (fig. 3) and then cut knock out the waste with a chisel. Then work the curve smooth with rasps or a spokeshave.
Here's an old blog entry I wrote years ago about special blades for cutting curves with a circular saw.
Note: I have realized that lately I'm spending a lot of time about what happens with things go wrong. The reason for this might be is that when things go right I don't think twice about it and I don't see the blog entry in it. Of course another possibility might be that banging my head against the wall is just the story of my life and I need to write about it.
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