This is my 10" Craftsman Radial Arm Saw, 1972 vintage. It is very important that the arm is exactly 90 degrees to the fence at the back of the saw table. Note the square. Pull the motor along its travel and see if the blade teeth follow the edge of the square exactly. It is quite common that a gap between the blade teeth and the square of a few thousandths of an inch will form as the saw moves back toward the end of the arm. This will cause inaccuracies in any precision cutting. The owner's manual gives a recommended procedure for aligning the saw, but it is difficult and does not work well. This Instructable will show you a much easier, much more precise way.
Step 1: The Factory Recommended Procedure
The recommended procedure involves loosening and moving the arm in its mount. Remove the two screws on the angle scale at the top of the column and remove the aluminum disc on which the angle scale is printed.
Step 2: Loosen the Mounting Bolts
Under the aluminum disc inside the column are two bolts. The heads are 9/16". With a wrench you are to loosen them just a little.
Step 3: Bump the Arm
After the bolts inside the column have been loosened a little, you are to bump the saw's arm a little and check the blade travel with the square again. When the arm is square to the fence, you are to tighten the bolts inside the column. Put the aluminum disc back in place and everything should be good again.
But, it is very difficult to bump the arm without bumping it either too much or too little. There is a much easier way.
Step 4: Adjust the Table With Precision
There is an easy way to move the table rather than the arm and move it just a little so the edge of the table that holds the fence in place is exactly 90 degrees away from the blade's travel on the arm.
Step 5: Loosen the Table Hold Down Screws a Little
When loosening the hold down screws for the table a screwdriver is required from above and a wrench to hold the nut below. Loosen the four screws in the table just enough that you can move the table, but it is not too sloppy.
Step 6: Make Two Small Blocks
Cut two pieces of 1 x 1 wood 1 1/2 to 2 inches long each. Get two 8 x 32 machine screws about 1 1/2 inches long. Drill a hole through each block just a little smaller in diameter than the screws. This hole is the black circle in the graphic. Thread the screws through their holes so some of each screw extends on both sides of its block. The yellow circles are optional holes for mounting screws. Glue may be sufficient in most cases. These blocks will be mounted on the underside of the saw table. (See the next step.)
Step 7: Mounting and Using the Blocks With Screws
The photo shows the blocks with their screws mounted in place under the saw table. The tips of the screws rest against the frame of the saw. With the table hold down screws loosened (Step 5), push the table forward so the screw tips rest against the saw frame. Tighten the hold down screws slightly. Secure the fence against the front edge of the saw table. Place the square as shown in Step 4 and check the alignment by pulling the saw motor down the arm to check the blade travel against the square. If adjustment is needed, as it surely will be initially, loosen the table hold down screws a little and turn the 8 x 32 screw in one of the blocks in or out a quarter turn. Tighten the hold down screws and secure the fence again. Check the blade travel against the square. After a few tries, the blade travel will be perfectly 90 degrees from the fence.
Where these blocks become very useful is when you must take down the saw for moving to a new workshop. But, they also make the initial setup easier and more precise. One day you may need to replace the saw table. These blocks will make alignment after that job easier, too.