One of the first woodworking projects to make after the purchase of a new table saw is a crosscut sled. Not only is it a fairly simple project to make, it will will serve you enormously with future projects. It will in it's various forms, allow you to crosscut at a 90° angle more accurately and safely and cut flawless 45° miters, for example for picture frames.
to get the sled's fence square to the blade. Also, it can be difficult to get the two miter slot bars properly aligned. So with this in mind, here is a design for a simple crosscut sled perfect for a starter project.
The pieces you will need are:
the base - approximately 30 inches by 20 inches of baltic birch plywood of MDF
one metal (aluminum or steel) or hardwood runner 20 inches long by 3/4 by 3/8 (to fit your table saw slot)
two pieces of wood, softwood/poplar is fine, one inch thick, 3 inches high, by 30 inches
one piece of wood, softwood/poplar is fine, one inch thick, 3.5 inches high, by 30 inches
The first step is to attach (screw/glue) the miter bar to the underside of the base about one quater over to one side. By having only one bar, you will avoid the hassle of aligning two different bars. Metals bars are obviously more durable than wood runners, which can become looser over time or stick with humidity. Metals runners can be bought a woodworking store, or you can buy longer lengths for cheaper at a metal shop.
The second step is to attach (glue/screw) two of the 'fences' to the longer edges of the base's top side. Do this relatively square to the blade, but it doesn't have to be perfect. This is the simple part of the design. These will be your front and back of the sled. Fences is in quotes because these are not actually your fence, but they are there to hold your sled together as you will be cutting your base into two pieces.
Third, fit the sled into the table saw and proceed to push the entire jig across the running saw. The saw must not be higher than the two fence pieces. Now you have a zero clearance kerf as long as you don't use a different saw blade with your sled.
Fourth step is the most crucial. Using an accurate woodworkers combination square, attach the real fence (the 3.5 inch high piece) square to the kerf. Do this by screwing in one side of the fence by the underside of the base so you can still pivot the piece. Align the fence square to the kerf and then clamp it into position. Screw the other end into place. Make sure the fence stayed square during this procedure and then secure it with more screws.
It shouldn't take too long to complete this crosscut sled project.
As you use the sled a few times, if everything was properly aligned, the kerf should not be enlarged with use. If the kerf is being enlarged, then some setting is wrong and you will have to recalibrate things. If you verify the sled and everything is perfectly adjusted, then the only other problem that might be causing an error is if the miter gauge slot was not square to the table saw blade. This would have been a factory sloppiness. In this case, you will have to adjust the arbor of the table saw to set everything square. If it does come to this, well, at least you figured it out early.
Finally, treat the sled like a precision tool. Don't leave it to kick around on the floor. Find a good spot to store it while not in use and you should be using this crosscut sled for years to come.