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I'm trying to fit trim on a square post. The trim goes around the base of the post where it meets a stone foundation. The trim is made from a fir 2x6 with the inside face (where it meets the post) beveled 20°, making the angle between the top face and the inside face 70°. I'd like to join the pieces with miter cuts at the corners.

The way I'm setting up the cut is to use an angle finder, similar to this one:

Angle finder for miter saw

to first measure the angle between the sides of the post, and then to transfer the angle to my miter saw using the laser guides on the saw to adjust the angle on the saw until the laser runs down the guide line in the center of the tool. The blade is set plumb to the table and the trim pieces are clamped to the saw fence so that the inside face is flush against the fence (in the same position as the trim will sit against the post).

After cutting both side of a joint, the angle between the inside faces does not match the angle finder and the piece does not fit the post exactly (the angle is a little wide (about 1/8" over 14").

I've double checked everything in my setup, and I can't find any mistakes. I'm looking for suggestions on how to troubleshoot this, and also a sanity check on my method – am I right in thinking that a piece of trim being used in a manner similar to crown molding can be cut at the "obvious" angle (e.g., 45° for an accurate 90° corner) when it is held in the saw in the same position that it will be in when installed?

  • The angle finder should be directly measuring the out-of-square situation you're trying to match so it's a good starting point. I can't figure out where the error is being introduced unless it's with the saw, assuming you are measuring the correct non-90 angle at the correct height (and that you're holding the tool level) and then transferring that to your saw setup. – Graphus Oct 19 '16 at 7:05
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Are you measuring the angle at the height you are placing the trim?

If so, instead of using the laser to line up the blade, lower the blade on the saw and use the side of the blade itself. Sometimes those lasers can be a few degrees off.

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  • I think the lasers are pretty close, on cross cuts I can split a pencil line I align with the laser, but I'll try this. I'm quite puzzled and open to anything… – dlu Oct 18 '16 at 4:51
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    Check things at every step and see where the error creeps in. Cut the board, and compare the angle of the cut with the angle of the gauge, If the piece is cut to the correct angle, then something is out of square on the post you are mounting it to. – LeeG Oct 18 '16 at 4:56
  • Should have mentioned that I'm doing that. Saw setup looks dead on, but cut doesn't match the angle on the angle finder (after cutting both sides of the miter). I'll go back and look for ways to do finer grained checking. My hope is that the angle finder takes care of any out of squareness on the post. Is that a bad assumption? – dlu Oct 18 '16 at 4:58
  • @LeeG, I missed the first part of your answer. Good thing to check, and yes, I'm measuring where the inside face of the trim will sit. – dlu Oct 19 '16 at 4:59
  • Just thought about this again, going to see what happens when I use the blade as my reference on the angle finder and compare it against the laser. – dlu Oct 20 '16 at 2:37

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