[I posted this as a comment here.]
A beautiful joint with no end-grain showing and really simple – right? NO!
Well the first part is right – they are attractive, but making a good miter joint is not as easy as it looks. And they get more difficult than just matching two 45 degree cuts together – there’s the compound miter joint that introduces another angel, or the mitered dovetail joint, and many other variations – all difficult to make.
I can always make a three-sided picture frame with perfect miter joints – it’s adding that fourth side where everything can go pear-shaped.
The problem is one of compound errors. What looks to the eye like a perfect 45 degrees, may actually be 45.05 degrees, or 44.95 degrees. Three pieces fit together well, but when you add the fourth piece you see you are out by .15 degrees.
If you can’t get your saw set up perfectly, there is hope. Make a sled with a 90 degree block split by the saw blade as close to 45 degrees both sides as possible. If you are out on one side by a little, you will be out on the other side by a compensating amount. Keep track of your pieces, mark them A & B cuts and make sure that you fit an A cut to a B cut all the way around.
Result? A PERFECT MITER CUT FRAME!
-- CanuckDon "I just love small wooden boxes!" http://www.hillsbiblechurch.org/