There’s been a number of questions about getting miters perfect.
Ellis Walentine: Depending on your blade and how accurately your saw (table saw, radial arm saw, chop saw) is set up, you may or may not always get a perfect 45-degree cut straight from the saw. My favorite way to true them up is with a stationary disk sander.
The secret is to make up a simple jig with a wooden or metal bar that rides in the sander’s miter slot. The jig consists of a scrap of plywood with one perfectly square corner. Screw the guide bar to the underside of the plywood at a 45 degree angle, so that the square corner just touches the sanding disk. Then, with a 100-grit disk on the sander, sand each miter cut by placing the piece against one plywood edge or the other. Move the jig slowly and deliberately as you sand to eliminate scratches.
This system works well because the 45-degree angle isn’t absolutely crucial, as long as the plywood is perfectly square, since you’re sanding all the left corners against one edge and all the right corners against the other.
Ian Kirby: To cut a miter, you will be holding the workpiece at an angle or you will adjust the cutter head to be at an angle. If, for instance, you are using a table saw, you angle the workpiece. If you’re using a chopsaw, you and the cutter head. As with any wood cutting operation, the process is trial and success ? you make fine adjustments to get the best results.
If you move the cutter head, then it’s usually possible to make fine adjustments from the controls. If you move the workpiece, you can adjust the fence using masking tape in different spots to make the minute angle adjustments.
Rick White: Cutting really accurate miters is one of the toughest tasks a woodworker will faceIt’s all about alignment, accuracy and making sure everything is just right. Up until recently, I just did whatever I could with an adjustable square. Not to toot my own horn too much, but I just helped Rockler design this miter gauge that really is the most accurate tool I can use to cut these difficult angles.