Hi Ron: Steve is correct....the best tool for this is a properly adjusted power miter box saw with a 44 to 60 tooth carbide blade.
But if you don't have the $150 to $300 for this tool, you can use your table saw, using the following procedures.
- Spend $40 to $50 for a good 60 tooth 10" blade. - Make sure your cross cut sliding guide cuts are 90 degrees to the saw blade. You can test this by making a cut on a piece of wood and then checking the 90 degree angel with a framers square. You may have to adjust the angle of the sliding guide a bit.
- Tilt the blade to 45 degrees, make a cut on a piece of scrap, then take the two cut ends, turn one over and match them on the inside 90 degree angle of a framing square. The two 45 degree cut faces should come together perfectly. If there is a gap in the heel of the angle (part of the 45 degree cut near the inside of the picture frame), then you need to decrease the angle of the blade slightly. You should do just the opposite if the toe (outside) of the angle has a gap. Cutting the correct length can be a bit tricky, but will be easiest if you keep your finish piece to the right of the blade, where it is much easier to see and follow your cut line.
One other trick: raise your blade only to the height necessary to cut your piece. You will get less tear-out that way.