The main reasons for not doing internal mitres are finding the angle, shrinkage on pine boards and by scribing you overcome both and you don't need to be too accurate on the length between corners.
If you really must do an internal mitre for whatever reason here's a simple cheat for the angle. A mitre only works when both halves have the same angle. So, get a sheet of paper and fold it to fit exactly into the corner, it's often not 90deg, then fold it in half. Set your saw to the angle you have created.
Chippy Mears
If you really must do an internal mitre for whatever reason here's a simple cheat for the angle. A mitre only works when both halves have the same angle. So, get a sheet of paper and fold it to fit exactly into the corner, it's often not 90deg, then fold it in half. Set your saw to the angle you have created.
Chippy Mears