Finish Carpentry Tips
Uneven walls or misaligned jambs make it hard to get tight-fitting miters. If your miter has a consistent gap at the front, there’s a good chance that putting a slight back bevel on both moldings will fix the problem. If you own a compound miter saw, you could tilt the saw about a half-degree, but that requires fussy adjustments.
The quickest and easiest way to cut a slight back bevel is to shim the molding so it’s resting at an angle to the saw blade. A pencil makes a handy shim and is just about the right thickness. You can adjust the position or thickness of the shim to compensate for all kinds of wall variations. You can even shim just the back or the front to mimic how the trim rests on uneven drywall.