What level of inaccuracy is considered tolerable for a miter saw?

Question

I have a brand new skil 12" double bevel compound miter saw. The fence is aligned properly - It creates a perfect 90% angle with the blade when set to 0 degrees. however, if I set it to 45 degrees on either side, it is actually cutting 44 degrees, meaning I have to set it to ~46 degrees to get a perfect 45 degree cut.

This is the first miter saw I have purchased, and I would think that for most projects this small of error would not really matter, but in this case I am making a large picture frame so having the sum of corners be 360 degrees is necessary.

Are miter saws expected to make cuts to accuracy of less than a single degree? Is there some other variable that I have failed to consider that may be affecting this?

Answer 1

It sounds like the detents and/or scale may be improperly calibrated. Sometimes the detents on cheaper saws also have some slop, so you may need to wiggle the blade one way or the other after locking into a detent and before locking the setting in place. Also keep in mind that you should tighten the adjustment knob to lock your setting in place even when using the detents, so the setting doesn't drift out of adjustment during the cut. If you're getting consistently wrong results, you might be able to loosen a couple screws and make a slight adjustment, but the saw you're using is an entry-level saw and may not be able to do much better. Higher-end tools are often easier to calibrate and hold their settings better once calibrated.

If you can't get the results you want with this saw as-is, you have a few options:

1. Don't rely on the detents or scale, and use a square or drafting triangle to set up your blade for a cut. If accuracy is important, this is a good solution regardless of how good your detents are. You can also get an aftermarket laser guide if your saw doesn't have one, but personally I'm not a fan of a laser guide.
2. Leave a little extra when making a cut, and clean up with your table saw (with a miter sled), hand plane and shooting board, or sander. A lot of people consider the miter saw a rough tool, and the only people I know who cut all the way to a line on their miter saw have very high-end models that cost $700+. But to be honest, I don't cut nearly enough miters on my miter saw to justify that kind of purchase.
3. Return the saw. If you think you got a dud, you can try getting another of the same model, or you can upgrade to a higher-quality (read: more expensive) miter saw.

Regardless of which of the above you choose, it's always good practice to make a test cut after making any adjustment to the tool. Also note that you may combine any of the above solutions. I only use my miter saw when a piece is too long to comfortably crosscut on my table saw, but when I do use the miter saw I usually cut a little outside my line and clean up on the table saw (option 2 above).

Answer 2

Different models and manufacturers have different degrees of accuracy, and there may be variation between samples as well. This was originally a construction saw rather than a fine woodworking tool, and some are still not much more than that. Accuracy of the detents, and ability to hold a position while being locked down, also vary.

Others, with some work tuning them and with a new blade designed for cleaner cuts rather than faster cuts -- and with some work setting up zero-clearance faceplates -- can reliably deliver accurate furniture-quality cuts.

The best advice I can give you is to dig into some of the woodworking magazines and find their "shoot-out" articles, which compare a set of similar tools head-to-head against each other and discuss what they think each got right and wrong. There's always some risk of a biased review, and your experience may not match theirs, but from what I've seen they do a pretty respectable job of narrowing the choice down to two or three models to investigate first.