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I don't yet have a table saw (just starting out and learning quickly here), but did come by a nice, used sliding compound miter saw from a friend who no longer had a need for it.

The issue I'm running into is that cuts I make on wider boards (10" or so) have an inconsistent kerf width, so when I go to join two cuts together the don't fit squarely because that cut is inconsistent across its length. I've carefully observed the effect and noticed that the wider portion of the kerf is closer to me where blade has effectively gone through it twice: the first time when the blade first makes contact with the board and travels through it, and the second time when the opposite end of the blade finishes traveling through it as I push the saw back towards its docked position.

I've spent a lot of time trying to square up the entire saw, playing with the fence, the 90° angle, and best as I can tell (which may be limited) everything is pretty on the line. But this issue of a wider kerf on essentially half of the cut on all my boards is stopping me from really being able to put anything together.

What steps should I be taking to try and make these cuts clean?

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    This isn't what you want to hear but the solution could be not to try to rely on the cuts straight from your saw. Although a better blade will possibly help it is entirely possible that your saw can't be tweaked to make a good enough/perfect cut. It's very normal to perfect saws surfaces, e.g. on a shooting board, for higher-quality work. – Graphus Mar 11 at 13:38
  • BTW you don't need a table saw. Although they can be extremely useful of course many experienced woodworkers don't own one and never have, even if they have the space and can afford one. Some people choose not to use them for various reasons (safety being one significant concern) and instead do many of the cuts that would otherwise be done on a table saw using a track saw or circular saw. Or sawing entirely by hand, although that's rarer naturally. – Graphus Mar 11 at 13:42
  • Thanks for the feedback @Graphus, that does make sense. I'm still hoping to find a way to do better, but it's good to realize that it just may not be up to it. I wasn't familiar with a shooting board either, but now I am, thank you! – Joshua Mar 11 at 17:01
  • If you make two pencil lines in the cut direction, slightly further apart than the kerf width, and cut between them, do you notice if the distance between the cut surfaces and the lines deviates in an interpretable way? In ASCII art form, cutting at the "X" (board-left) | X | (board-right) gives (board-left) / and | (board-right) or (board-left) / and \ (board-right) ? – C. Chang Mar 11 at 23:03
  • Assuming you do find that you can't tweak the saw or adjust sawing technique to give good cuts I'd suggest you not immediately think of upgrading the blade, instead what saw(s) do you currently have available as alternatives? If you have any suitable hand saws even without experience you can get great results using the appropriate method, one of the best being running the saw along a straight edge, which helps you keep to your line as well as ensuring the cut is more square (although either defect is tweakable using a belt sander or hand plane, either freehand or using a shooting board). – Graphus Mar 13 at 7:57
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When the blade is entering through the board, it isn't stabilized by the surrounding wood, so it may vibrate a little more than when it's moving forward through the cut. This is probably why the kerf is wider nearer to you. My guess is that if you did the whole cut coming from above one blade-length at a time, you would have the wider kerf all the way through the board. (Not a good way to cut, but it may shed some light on what's happening.)

So, if that is the issue, you could try first making a shallow initial cut about half a blade-width towards the waste side of your cut line. I'd say keep the depth at 1/4" or so, if your miter saw has a depth stop. Keeping the cut shallow should reduce the variation in stability between different parts of the cut, and when you go back to do the main cut, the blade should be stabilized and enter more cleanly.

If that doesn't work, have you tried using a different blade? There are "thin kerf" miter saw blades out there. You could also try a blade with a higher tooth count with a low hook angle.

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    +1 My feeling is that if a new blade might be the solution, or at least help, wouldn't a thicker blade be less prone to vibration? But since the saw was used it could be there's wear on the arbor, in which case vibration could be inherent to the running of the saw unfortunately for the OP. – Graphus Mar 12 at 6:27
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I have a hunch that the problem with your saw is that the plane of the saw blade is not exactly parallel to the up/down and back/forward paths of the saw motor. This could be caused by:

  1. A bent saw blade
  2. Some debris clamped between the saw blade, the inside blade thrust washer and the shoulder at the inside end of the saw shaft
  3. The motor not mounted with the shaft perfectly at right angles to the intended up/down and back/forward blade path as dictated be the slides and motor raise/lower articulation arms.

If you can correct these issues your blade should follow a truer path. Note that a used saw could have been dropped at some point causing the misalignment or even bending part of the saw.

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