How do I verify a 45 degree miter?

[Cliff Newton]

I'm not sure if my miter saw is cutting at an exact 45 degrees. Is there some special technique I can use to verify it?

[Tyler Howell]

A good combo square has a 45* angle that you can use to check the finished cut on a piece of scrap

[Bob_Hammond]

Cut two pieces with 45 miters, and put them together to form a 90. If it isn't exactly 90, then you need to adjust it.

Bob

[Mark J Bachler]

Cut two pieces with 45 miters, and put them together to form a 90. If it isn't exactly 90, then you need to adjust it.

Bob

Yep, what Bob said.

[Steve Jenkins]

Cut 4 pieces exactly the same size they should form a square. You can check the joints visually without any other tools.

[Ted Shrader]

Cliff -

Do as Steve said to check 90°.

Extending this a bit further -
You can also check other common angles that make a closed form. ie 30° for hexagon, 22½° for octagon etc. If the angles are not right on you will have a gap when the last piece is inserted.

In practical application, though, glue the pieces together to make two halves of a shape, then slightly trim the ends on the two halves to get a perfect fit.

These techniques come in to play making segmented bowl parts.

Ted

[Byron Trantham]

I use the "create a 90 degree method" also. I also use a draftsman plastic 45 degree triangle to check the blade to the fence. They can be long enough to check with the saw all the way out to the end of it cutting capability. The plastic is thin enough to fit between the teeth.

[Scott Banbury]

Cut 2 90s and put them together end for end and see if the resulting edge is straight.

[Marshall Harrison]

All of these "cut and put together to form square methods" are great.

But they won't give you an accurate picture unless the blade is parallel to the miter slot.

[dale rex]

I have used all of the methods described, but still like to depend on an accurate square to make my final adjustments. I used to rely on a Stanley square for my setups, until I bought a Starret square recently. What a difference!The Stanley square was way the heck off!The Starret was expensive($65),but guaranteed to be accurate.

[Dave Crabbs]

Cut two 45* miters on 2 different boards of the same width (cut a left 45 and a right 45) and put them together with the long point to short point they should make a stright line.

Dave