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Protractors and Miter- Saw Gauges Gary Katz Figure 1. Reading an angle with a protractor or angle finder is easy, but transferring that angle to a miter saw can be a nightmare. IT’S EASY TO READ ANY ANGLE with a protractor, and easy, too, to split that angle in half in order to determine the correct miter. [Fig. 1] But it’s not so easy to transfer that angle to a miter saw. Why? Probably because the first miter saws were designed by engineers, not carpenters, and the numbers on your miter gauge are actually the complementary numbers for every angle you’re cutting. For those of you who are still as confused as I once was, before I get to the solution, let me explain the problem. If you set your saw at “0,” you’re actually cutting a 90° angle (a butt cut); that’s the angle of the From Mastering the Miter Saw DVD 90° Figure 2. We all know that this is a 90° angle. 45° Figure 3. And we know that this is a 45° angle. ©2004 Gary Katz, OnSite Productions, LLC fence to the blade. [Fig. 2] If you swing your saw to 45°, you’ll be decreasing the angle between the fence and the blade and cutting an acute angle. [Fig. 3] As you swing the saw toward the fence, the angle gets smaller, more acute, right? So why do the numbers on the gauge get bigger? Let’s not go there — yet! Instead, remember that your fence is set at 90° to the blade (when the miter-saw gauge reads 0), which means that the more you swing your blade toward the fence, the more you’re subtracting from 90°. To resolve the confusion forever, take a permanent marker and write down the correct angles on your www.garymkatz.com page 1 Figure 4. True Miter-saw Angles To avoid confusion, write the correct angles (shown here in red) above the numbers that appear on a standard miter-saw gauge. Miter-saw fence Blade 30 60 30 60 4 45 5 45 5 4 67 1 22 1 ⁄2 ⁄2 6 30 0 60 0 3 miter-saw gauge, above the ones that are already there, ie.: 0 = 90; 10 = 80; 20 = 70; 30 = 60, etc. [Fig. 4] There are a few saws on the market that are manufactured with the correct angles; the new Bosch 10-in. 44-10 is one of them. And yes, that’s right, the 221 ⁄ 2° mark on your gauge is really a 671 ⁄ 2° angle! That’s one of the reasons we’ve all been confused for so long. In the future, when you see an angle like the one in Fig. 5, try to think of it as a 135° angle — the miter angle is 671 ⁄ 2°. And remember, if you want to cut a sharper, more acute angle, swing your saw past 45,° where the angles get sharpest. [Fig. 6] Most saws will cut at least to a 40° angle. My Bosch miter saw will cut 30° to the right and 40° to the left. So, what happens when you put an acute-angle jig on your miter saw? You’re simply changing the angle of the fence to the blade. [Fig 7] With an acute-angle jig made at a 45° angle, the saw fence is set at 45°, so the more you swing the blade toward the fence, the more you’re subtracting from 45°. You can even use the “confusing” numbers supplied by the saw manufacturer by doing the math backwards: If you want to cut a 15° angle, subtract 15 from 45 and set your saw at that difference: 30. 75 15 90 0 Figure 5. We’ve all learned the hard way that this angle requires 221 ⁄ 2° miters. But this is really a 135° angle and requires 671 ⁄ 2° miters! 75 15 1 ⁄2 67 1 ⁄ 2 22 Figure 6. After all, a 221 ⁄ 2° angle would look like this! Figure 7. This acute-angle jig effectively shifts the angle between blade and fence from 90° to 45°. From Mastering the Miter Saw DVD ©2004 Gary Katz, OnSite Productions, LLC www.garymkatz.com page 2