I need to know a machine or device that will cut true 45° every time. I make picture frames from solid wood, and my 12″ compound miter saw will not always cut a true 45 degrees.
John Brock: The accuracy of a machine is a function of the person operating that machine and the consistency of their techniques. Several years ago I was at a woodworking show and watched a demonstration showing the use of a Dubby® board for cutting accurate miters on the table saw. I purchased both the left- and right-hand versions and eagerly took them home. Part of the installation and setup of the Dubby boards was to accurately align the miter slots in the saw with the blade, and to dial in the jig itself. The accurate and complete instructions stressed some important but easily overlooked details, like always pressing the jig against the same side of the miter slot. The setup instructions that came with those boards were like gold. Yes, I still use my Dubby boards regularly.
Mike Van Pelt: I would take a serious look at the Pootatuck Lion Miter Trimmer. This machine is built for precision miter work and will work very well for your application. Do not be fooled by cheaper imports; the Lion miter trimmer is the best.
Carol Reed: Use a drafting triangle to set your compound miter saw to 45°. Do not rely on the settings on the saw. They are not accurate enough. If the saw truly will not hold that setting, you are in the market for a new saw. You will still need the drafting triangle to accurately set the proper angle.