Nearly all radial-arm saws are designed with a metal base to which a replaceable wooden surface can be affixed. While there are other stationary saws that also use replaceable table surfaces, the design of the radial arm saw is such that the table surface needs to be replaced more often. The radial arm features a raised motor and saw blade which cuts stock from above. This means that the saw blade cuts slightly down into the table top on virtually every cut, and over time the table surface becomes filled with grooves from the blade. The saw is engineered in a way that makes it easy to replace this table top when it becomes badly marred.
The Table Top Construction
If you look closely at the tabletop of a radial arm saw, you will see that it is constructed of three pieces: a large open expense of tabletop which supports the stock as you cut it; a small vertical fence set just behind the main table top; and a narrower section of tabletop that abuts the back of the fence, essentially sandwiching the fence between the two horizontal segments of table top.
The bolts that secure the tabletop to the metal table of the saw are usually machine bolts that fit into counterbored holes in the tabletop. The counterbores allow the bolts to be recessed far enough down that the saw blades can't contact them when it is drawn across stock during cutting.
Best Surface Materials
While any type of sheet good material could be used for the tabl top on a radial arm saw, the best material is MDF (medium-density fiberboard. MDF is inexpensive, pretty durable (as long as it doesn't get wet) and it doesn't splinter when the radial-arm saw's blade cuts through it. Plywood, which is made of layers of wood plies, can begin to splinter and break apart as it becomes filled with saw cuts.
How to Replace the Tabletop on a Radial Arm Saw
The easiest way to replace a tabletop is to remove the old table top, cut pieces of MDF to the exact same size as the front tabletop, the fence, and the back tabletop pieces. You'll then drill the horizontal pieces with the same counterbored holes as in the old tabletop, then bolt the new tabletop down in exactly the same fashion as the old one.
However, there are two critical things to watch for when installing the new table top:
- The tabletop surfaces need to be exactly parallel to the bottom point of the saw blade at all points along its travel along the arm.
- The fence needs to be installed exactly perpendicular to the vertical plane of the saw blade set to cross-cutting position.
Testing for Parallel Tabletop
When installing a new surface, you will need to make sure that the travel of the radial-arm saw is parallel with the table surface at all positions. To test this travel, set the angle of the radial-arm saw to the 90-degree cross-cut position, then lower the radial-arm saw until the blade is barely touching the surface of the MDF. Pull the saw forward along its track. The blade should neither dig into the surface or lift away as the saw moves the length of its travel. If it raises or lowers as you pull it across the surface, you'll need to adjust the table. Most saws have adjustable rails on which the tabletop rests, and these rails can be adjusted up or down to ensure the blade is square to the table over its full run. Or, you can place shims under the MDF surface as it sits on the frame rails to adjust it before bolting it down.
Installing the Fence
Once the horizontal front surface is true to the travel of the saw, the only thing left is to install a fence. A recommended fence is a 2 1/2-inch wide piece of MDF set on edge. The fence can be attached to the edge of front horizontal piece with a few MDF screws driven through the back of the fence and into the edge of the front tabletop. The space behind the fence is the filled with a rear tabletop piece and bolted to the frame below.
The fence needs to be installed perfectly square to the saw blade. This is normally done by adjusting the "heel" of the saw so it is at a perfect 90-degree angle to the fence when the saw is set in cross-cutting position. If you have cut and installed the front table segment correctly, this should be a minor adjustment.