How to miter angles greater than 90°?

[MickeÖ]

I'm working on installing trim in a portal that follows a sloped ceiling, and I just can't figure out how to calculate the miter angle. According to the digital angle finder, the angle is 156°, and dividing by 2 like with regular corners doesn't quite work. I solved it by cutting test pieces until they fit, and then the angles that matched were around 10°, but I don't understand the math behind it. The saw has 90° as zero, which is probably causing the issue, but there has to be a simple way to calculate it?

 

[danbanan2]

156° Divided by two equals 78°
The saw has, as you write, 90° as zero. Therefore, you should set the saw at 12° for them to fit.
90° - 12° = 78
Should be correct like that...

 

[MickeÖ]

But of course...thanks for the help.
sometimes the brain doesn't want to cooperate :blushing:

 

[Dräpe]

Just want to bring up this thread again to thank danbanan2

Sometimes you just can't figure it out. Thanks!