Miters, of all types, seem to give many woodworkers agita. And that angst isn’t just limited to crown or base moldings, it holds for nearly every type of miter a woodworker can imagine. The reason for such apprehension comes, I think, from most miters being directly visible on the completed piece. There’s nothing like investing weeks, months or even years of effort into your masterpiece and being forever reminded of that one miter mistake.
Sometimes the problem is purely mechanical in that the angles were just improperly cut, but that’s not always the case. We may set our miter saws, or miter boxes, to a perfect 45° angle and still end up with minor gaps in our miters. A bit of dust or errant whisper-thin cutoff clutters the corner of our saw’s table and fence and all our attempts at precision are blown.
Worse yet are the times when we’ve taken extra care to ensure everything is perfect at the saw only to destroy the fit when fine tuning the joint with a hand plane. Touching up the surface of a miter with a plane can leave a surface that takes glue sizing better, providing a stronger joint in the end. But tipping the plane slightly off square or taking half a shaving too much off the heel or toe of the miter can create cavernous gaps. And if you compound the problem by duplicating the miscut on both halves of the joint you’ll end up tearing your hair out or starting this phase of the project over (or both).
In this week’s article for 360 WoodWorking members (read it here), I’ve described a handful of techniques you can use to tighten up those miters and there’s even a video that shows how I apply the techniques in different situations. And while I won’t divulge all the information here, I can tell you one of the tips I discovered that brought my miters together better was proper bisection of the angle. And before you run off thinking this is going to turn into a complicated geometry lesson, let me tell you that the method is extremely simple and involves no mathematical calculation whatsoever.
All you need is a couple of sticks that are as wide, or wider, than your molding (but they both need to be the same width). Lay them exactly in place where the molding will end up. Overlap the sticks at the point where they need to be mitered. On one of the two sticks, mark the inside and outside points of the overlap. By connecting those two points, you’ve accurately bisected the angle and you didn’t even need a calculator.