It's not difficult to measure a picture frame, but cutting the four strips of molding requires a high degree of precision. It's essential that each set of matching molding strips are cut exactly to the same length. If they aren't, the frame will not have square corners. Also the 45-degree corner miter joints must line up precisely to create a professional looking picture frame.
How to Measure Picture Frame Molding
Mount the miter box on a table. Take the wood base off the miter box, and set it on a wood work surface. Drill two holes all the way through it. Countersink the holes. Screw the base securely to the work surface with wood screws, making sure the heads of the screws are seated below the surface of the wood.
Lay a strip of molding in the miter box base face up with the outside edge of the molding pressed flat against the outside fence.
Insert the hand saw into the miter box to do the first cut, making sure there is wood on both sides of the blade while making the first miter cut. With the non-sawing hand, grip the strip of molding tight to the miter box fence. Upon completing the cut, the longest part of the miter cut is resting against the fence of the miter box.
Take the newly cut strip of molding, and lay it face down on the work surface. Lay the metal ruler along the narrow strip of wood that is the backside of the face of the molding. Measure from where the molding forms a right angle all the way down the strip, (i.e. if cutting a frame for a 9x12-inch piece of artwork, and this strip is to be for the 12 inch length, measure 12 inches plus 1/8 inch). The extra amount is to insure you can insert and remove the artwork easily. Make a mark with a very sharp pencil.
Take the carpenter's square, lay it alongside the pencil mark and draw a line. Keeping the square where it is, slowly flip it straight up, and draw a second line on the backside of the outside edge of molding.
Rotate the molding so it's now resting on the outside edge. Make a clear mark on the inside edge of the molding. Accuracy here is crucial.
How to Cut a Finished Length of Picture Molding
Slide the molding back on to the base of the miter box with the side of the molding flat against the fence. Look at the first 45-degree angle cut. This second 45-degree cut must be just the opposite of the first cut.
Locate the mark on the inside edge of the molding, and line up the saw blade. Grip the side of the molding tight to the fence and begin sawing. Once the sawing begins, the molding can not move even a fraction of an inch.
Saw slowly and evenly all the way through the molding