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I am a very amateur woodworker that's just getting started using my DWS 779 miter saw. My recent projects have been making bird houses with flat bottoms that have a 2" wall surrounding the floor. While my question is about 45 degree angles, it could be any angle for my saw.

It can dial in 45 degrees on both side for mitering. I cut a board to length, give it a 45 degree miter, then rotate the miter to the other 45 degree miter and cut. When I go to take those four boards and make a box out of to frame the bottom piece, the angles are slightly off and I end up having to use a little bit of wood filler to fill in imperfect joints.

Is there a reason my miter saw's 45 degree (and really all of them) are different on one side or the other? I would admit that it could be how I'm using it as well.

Here's an example of my boxes:

An oak wooden box base

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    Welcome to WSE. A quick workaround for the problem might be to cut both pieces using the blade in the same position. Cut one piece with the acute angle out and the other with it facing in. Any error in the blade angle will be addressed since the two angles are complements of each other.
    – Ashlar ♦
    Commented Nov 8, 2022 at 1:52
  • That's such a simple and great idea. I just thought to myself that I needed to "other angle", but that's a great idea.
    – Avogadro ♦
    Commented Nov 8, 2022 at 2:01
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    Since you're a beginner, the face-in, face-out thing @Ashlar describes is useful far beyond just this one use-case. The same principle is used by many in jointing edges on the jointer and in various cutting operations on the table saw. Basically anywhere that you want angles to 'match' you can work around the possibility that they won't actually match by creating complementary angles that cancel each other out. Coincidentally one of the most recent videos on Fine Woodworking's YouTube channel, on how to joint correctly, demonstrates this. But there are many other guides showing the same thing.
    – Graphus
    Commented Nov 8, 2022 at 4:29
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    "Is there a reason my miter saw's 45 degree (and really all of them) are different on one side or the other?" A dirty secret of woodworking is that the angle guides on machines are notorious for not being accurate. Not absolutely accurate. Many are close enough for the majority of work..... but mitres are a case when absolute accuracy is important. Even a fraction of a degree off is enough to be noticeable in mitres because the error is compounded — effectively an error as seemingly trivial as 0.1° multiplies to nearly a full degree out on any rectilinear work, once all corners are closed.
    – Graphus
    Commented Nov 8, 2022 at 4:31
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    Unrelated, but since you have a DWS779, you'll want to know that there's a recall that includes some copies of that model. Check the notice for details. It looks like you can sign up and get a kit with improved parts.
    – Caleb
    Commented Nov 9, 2022 at 3:38

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Have you checked your saw to ensure that when you set it at the 45° stop, the blade is actually 45° to the fence? That tuning process, ensuring that the miter stops (and gauge in general) are set accurately is part of the initial setup process. You should also check to ensure that the blade is 90° to the table.

These should be checked somewhat regularly. Like any time you need to make a critical cut. If you discover that the miter gauge is off, it's a matter of loosening a couple of screws, setting it right, then tightening them back down.

Currently, I'm using my DWS779 (consider getting the shadow line upgrade kit, BTW, well worth the extra cash!) for cutting vinyl siding. If I'm cutting at 44.7° instead of 45°, it doesn't really matter much. However, I double checked with my speed square before starting the project anyway. I've not bothered during the project, but most certainly will before I use it again for any important cuts/woodworking projects.

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