What size wood are you cutting? Are you framing a building, building a box, or making a picture frame? In other words, how precise do you need to be?
If you know the length of the piece you need, cut the first 45, then measure the long side and mark it. Remember, it's an opposite cut. To help me, I use a saddle square that has a 45 on one leg. It gives me the right cut direction as well as a perfect line at 45.

 

I sold cabinetry and lighting for 2-1/2 years. Framing was a joke as I have seen houses off square as much as six inches from one end to another. Never saw a carpenter's square at a construction site during that time.
Back to the topic- good information to keep for reference. Pondering framing some photos.

 

I'm not sure if this is what you are asking, but if you cut a 45 degree angle on a board, the difference in length between the short side of the board and the long side will be equal to its width.

In other words, if you take an 8-foot 2×4 (which is 3.5 inches wide) and cut a 45 degree angle on one end, the shorter side of the board will measure 92.5 inches. (96 - 3.5 = 92.5)

Do the same to an 8-foot 2×6 (5.5" wide) and the short side will measure 90.5". (96 - 5.5 = 90.5)

 

Good point Charlie. I didn't know that ;-)) I don't quite understand the question either. Sounds like care in cutting on the line might be part of the issue with 1/8 variance.

 

Sounds like cutting on the wrong side of the line. If he is using a miter saw and you change from one side to the other for the second cut then you need to cut on the other side of the line. A blades thickness is about 1/8 inch….?

 

if you make it 1/16 or 1/32 longer everytime and use a plane and shootingboard
to sneak up on it you get right evrytime and take care of slightly out of angle at the same time

Dennis

 

thanks guys, just trying to get a handle on the "how to measure" so I can make consistent 45 degree cuts for whatever I am making.
As I understand it, I measure the dimension of what i am framing. e.g. 8 in width. make one cut, then measure the inside dimension, mark the 8 in plus 1/16 for the opposite cut.
I get the blade thickness and take it into account.
As a novice, I get confused about measuring and marking….correctly consistently.
Thanks for your help. Appreciate it.
Dan

 

Its a good question, and Charlie enlightened me as well. I typically leave one side a bit longer and then sneak up on it.

 

also, if it's always 1/8" shorter try aligning your saw blade on the other side of the marked line. the kerf of the blade is 1/8" by itself which might explain why you are always 1/8" shorter - just a thought

 

Typically it is much easier to measure the long side of a miter. The point of the miter is a much more precise point to referece. The obtuse angle of the short side is easy to mismeasure.
I also prefer to transfer dimensions rather than measure. Every time you measure you introduce possible errors. Just on one side of the line or the other everytime you measure and every time you mark. If you can transfer the dimension, the measurement does not matter! This is why a story stick is so useful in stair or cabinet building.
Hope that made some sort of sense. Good luck, BTKS

 

I always leave a little on the length and then nibble it down with my guillotine….doing this with each piece ensures a more accurate angle and a smoother more snugged up fit…

=0)

 

I've been reading these comments hoping to find the simple answer to my question. I have a new kitchen island that I'm going to put a piece of 1/8 inch thick veneer to give it a nice finished look. I need to make the two 45° angels one reversed to get the clean 90° corner. If my island is 53 3/4 inch do i need to measure that length on the short to short or the long to long?