Accuracy of miter saws

[Burt Alcantara]

If you placed a 6" wide board up against the fence of a miter saw and made 4 45 degree cuts, would they align into a perfect square?

I'm able to do this with my new Incra 1000SE but only to under 3".

Just curious.

Thanks,
Burt

[Howard Acheson]

The only way to know is to test it. Some may be accurate enough, some may not. But, don't count on it until you try it.

[Larry Fox]

My CMS is for rough cuts only. I have the Delta and I don't trust it. I have never been able to get it setup to the point where it holds a setting.

[Joe Chritz]

Yes, no and maybe.

It depends on how well you set it up. I have gotten perfect 45 degrees with the Dewalt I have but I can't move it about and take it back and expect that every time. It is well within a 1/4 degree every time on the stops however.

If you want to be able to go from 90 to 45 and back and expect perfect it is unlikely to happen. A little tweaking (which takes a scrap piece or two and a few minutes) and many will do it fine.

If you will be doing a fair number it is probably better to build a dedicated sled for the Tsaw. It doesn't take long and is a great way to get repeated accuracy.

Joe

[Rick Fisher]

I wonder if you cut one board on the left side of the blade and the other board on the right side, face down, would it not be bang on?

[Tom Veatch]

I wonder if you cut one board on the left side of the blade and the other board on the right side, face down, would it not be bang on?

It would be if the object were to rejoin them in a straight line. That would simply be a scarf joint. If the object were to rejoin them as a square corner, then it wouldn't work. Set the saw to, say, 40° and give it a try with a couple of pieces of scrap.

[Chris Padilla]

I wonder if you cut one board on the left side of the blade and the other board on the right side, face down, would it not be bang on?

Rick,

Yes, the error would cancel out and give you two boards that meet up to create a 90 degree angle.

But if you wanted to create a perfect picture frame, it will not work out so well because the "length" of the miters will be different:

Take Tom's idea and calculate the hypontenuse ("length" of the miter) of the resulting triangle left after a "not so 45" 45 degree cut. Use 40 degrees as an extreme (instead of 44.9 degrees, for example) and 50 degrees (instead of 45.1 degrees) and you'll see what is going on.

[Dave Falkenstein]

No matter what tool you use to cut miters in wide material, you must be certain the material is not moving during the cut. When cutting a miter angle, the material will have more of a tendency to move than on square cuts. Be certain to clamp the work piece on every cut to make an accurate cut. Then adjust your saw or miter gauge with test cuts to result in perfect angles.

[Brian Kincaid]

I made a 'jig-fence' that I clamp to my miter saw's fence. My 90degrees cut is spot-on. I set the saw to 90 degrees and cut the fence.

Now I set to 45 degrees and I cut one piece on the miter saw fence, the other on the jig-fence. When joined they make 90 degrees.

The saw doesn't move so the error cancels. My joint is 90 degrees.

I cut two pieces at a time (top+bottom) and (left+right) so the pieces are the same length.

Brian

[Burt Alcantara]

I have a Harbor Freight 10" SCMS. Works great for getting 2x down to size but otherwise no accuracy. I have a number of boards to cut with these miters and was wondering if there was any benefit in getting a larger and better machine.

So far, your posts are not convincing me that the miter saw would be any better then the table saw. Guess I was also looking for an excuse to buy yet another tool that I don't really need.

Thanks,
Burt

[Michael Panis]

I made a 'jig-fence' that I clamp to my miter saw's fence. My 90degrees cut is spot-on. I set the saw to 90 degrees and cut the fence.

Now I set to 45 degrees and I cut one piece on the miter saw fence, the other on the jig-fence.....

Brian

Interesting...I'm picturing something fairly bulky attached to the saw. Do you have a picture?

---Mike

[Bill White]

that you take hold of the grip on the HF MS and try to wiggle it from side to side while the saw is extended. The ones I have seen/tested have a BUNCH of "slop" in the mechanism. There's where the errors originate.
My old and trusty cast iron (heavy as h7ll) Delta MS is not a slider, but it sure does give me some accurate cuts.
Set up is very important, but it ain't worth squat if the machine has inherent flaws.
Bill

[William OConnell]

If you placed a 6" wide board up against the fence of a miter saw and made 4 45 degree cuts, would they align into a perfect square?

I'm able to do this with my new Incra 1000SE but only to under 3".

Just curious.

Thanks,
Burt

Yes if its setup correctly. All miter saws however are not created equal so your question is too broad.
Having said that, I routinely cut miters of that size on my slider saw

[Tom Veatch]

...Yes, the error would cancel out and give you two boards that meet up to create a 90 degree angle...

Chris, I can't go along with you on that one.

Assume you're going to miter a simple, flat, rectangular board so it doesn't matter which is the front side or the back side. Set your miter saw to 30° and cross cut the board. What you have is the OP's left side cut in your left hand and (since it doesn't matter which side is the face side) the equivalent of the OP's right side cut in your right hand. Of if you want, you can flip the right hand side over and make another cut (the offcut will either be an equilateral triangle or a regular trapezoid with 60° acute angles on each end). In either case you wind up with two boards with a long side and a short side and and acute angle between the cut and the long side of 60°. Not gonna make a square corner with those two boards.

30° (15° error) is an exaggeration, but the principle is the same even if the miter saw cuts 44.9°.

[Tom Veatch]

I have a Harbor Freight 10" SCMS. Works great for getting 2x down to size but otherwise no accuracy. I have a number of boards to cut with these miters and was wondering if there was any benefit in getting a larger and better machine.

So far, your posts are not convincing me that the miter saw would be any better then the table saw. Guess I was also looking for an excuse to buy yet another tool that I don't really need.

Thanks,
Burt

I use a SCMS primarily for convenience. I usually keep a rip blade in my table saw and a cross cut blade in the SCMS. But, I also make test cuts and adjust as needed if accuracy of the miter cut is critical.

(I had one of those HF boat anchors in miter saw clothing at one time. I feel your pain.)