DIY & Home Improvement

Cutting and flipping the board will always form a 90 degree corner. Because your'e starting with a 180 degree "corner", also known as a straight board.

When you make one angle flatter (47.5), the other angle must become steeper (42.5) so that the result still adds up to 90 degrees*. You can't cut a straight board once and get two 47.5 degree cuts. It will take two cuts.

* The way this part works is a bit complicated to explain, especially without illustrations. You start with a 47.5 degree cut and a 132.5 degree cut, because we're measuring the angle from one side of the board and your cut split a 180 degree angle. Flipping the board over and measuring from the opposite side changes your frame of reference by 90 degrees. So that 132.5 degree cut measures as 42.5 degrees once the board is flipped and you measure from the opposite side. And 42.5 is not 47.5 so they don't come together perfectly.