I have had to replace the switch on my Sears Craftsman radial arm saw several times. I use a pushbutton single pole, single throw (SPST) switch from Radio Shack. It is stock number 275-671. The retail price is $ 5.99 US plus sales tax.
(The red rectangle is a label with my name. To be cautious about Internet security I made it illegible for this photo.)
Step 1: My Radial Arm Saw
This Instructable applies to Sears radial arm saws that look like this one (The photo is from an earlier Instructable.) This series of saws was made from the late 1940's through the early 1970's. My saw was made in 1972.
Step 2: The Original Switch
I no longer have an original switch, but used a photo editing program to create the image of an original switch in place. It had a red button to stop the saw and a green button to start the saw. The yellow arrow points to a keyhole for a stamped metal key used to lock the switch so the saw cannot be turned "on" accidentally. Metal tabs flank the green button to avoid accidentally bumping it and turning the saw "on" when not intended.
The main reason I no longer use the original style switch is that it was no longer available through Sears parts depots just a few years after I purchased my saw. In addition, these switches lasted about six years for me and (at the time) they cost more than twice as much as the Radio Shack pushbutton switch I used to replace the original design. I am now on my 2nd switch from Radio Shack. The first one lasted 26 years for me!
Step 3: The First Step
Whenever using a substitute electrical component check to know the voltage and current ratings you need to match. The motor on my saw has a plate that covers the top of the motor. Under this cover is a junction box where wires can be reconnected so the motor runs on 230 volts or 115 volts. Since I live in the USA, our usual current outlets supply 115 volts. I use my saw with 115 volt power.
This plate also gives the current ratings. My saw draws 10 amperes of current at 115 volts, or 5 amperes at 230 volts. The switch I got at Radio Shack is rated at 10 amperes for 115 volts, or 6 amperes at 230 volts. The Radio Shack switch is a good match.
Step 4: Mounting the New Switch
In order to find a place where I could mount the new switch, I had to turn the casting that holds the switch end for end. Then the body of the new switch had to fit into the hole in the cast iron saw arm. One of the original screw holes for mounting the casting that holds the switches is shown by the blue arrow. I had to move the casting back a little and make a new threaded hole as shown by the yellow arrow. An additional new hole had to be made for the other end of the casting, too.
I also had to drill a 1/2 inch hole in the casting for the threaded portion of the new switch. I made this hole between the original location for the green button and the keyhole. There really were no other places with enough space. See the photo in the Introduction.
Step 5: Wiring the Switch
The original switch had four tabs for both black wires and both white wires. The new Radio Shack switch has only two tabs. Fortunately, the tabs were the same size so I could simply slide the connectors on the black wires ("hot") onto the new switch. I cut the old terminals from the white wires ("neutral"), stripped them, and connected them with a twist wire nut.
Step 6: Safety Lockout
It is a good idea to provide a lockout so the saw cannot be accidentally started. A wooden block with a hole to fit over the switch button works very well. Put it into your pocket when using the saw so you do not lose it. Or, tie a short string to the coiled power cord and to the wooden block.