Nuts and Volts - December 2015

that has been placed over their locations. This is not the most accurate way to locate the holes, but this device does not need a lot of accuracy so it’s just fine. Be sure to take the interior features and location of the jacks into account when doing this. Each hole location was punched to make a dimple which helps to start the drill on center. The holes were drilled on a drill press, starting with a 3/64” drill to make small pilot holes and then with the final size drill (as shown in Photo 3) which follows those pilot holes. When using this two drill procedure, the location of the final hole will be accurate to a small fraction of the size of the small pilot drill.

The plastic housing was held in a drill press vise to prevent it from being grabbed by the drill and dangerously spun around. The drill was fed downward slowly. A hand drill could also be used with the cover held in a bench vise. The 15/64” hole is just a few thousandths too small for the stem of the switch, so a round file was used to enlarge it just a bit. About a half dozen strokes were enough to do this. A countersink was used to remove the sharp edges of the holes both inside and outside, and to bevel the edges of the cable holes (Photo 4).

A trick was used in mounting the switch. Most toggle switches have a keyed washer that prevents the switch from rotating in its hole. These keyed washers have an internal key that fits in a key slot on the barrel of the switch and a bent tab on the outside diameter that is intended to fit in a small hole drilled near the main hole for the switch. In spite of careful measurement and drilling, this bent tab often does not fit properly, so a different method was used in place of drilling.

The switch was placed in the hole in the case and the keyed washer was placed on it on the outside, with the tab resting against the plastic. Then, the nut was put on just finger tight so it would not move around. A hot (600º F) soldering iron with a small tip was placed on the washer just above the bent tab, and light pressure was applied until the tab melted in and the washer was flat on the surface of the cover.

Be careful not to go too far; a gentle touch is best. This worked perfectly and the appearance is very nice. It looks a lot better than a drilled hole. I wish I had thought of this trick about 30 years ago.

The wiring is done on the switch first, one row at a time. The two sides of the switch are labeled “Fax” and “B.P.” (bypass) to help. Keep in mind that most toggle switches make contact from the common terminals in the center row to the terminals on the side row that is OPPOSITE to the direction that the switch is thrown. This can be confirmed with an ohmmeter. The first row that is wired is side #2 on the schematic, or the bypass side. Two yellow jumpers on this row can be seen in Photo 5.

Next, four wires are soldered to the terminals of row C on the switch, or the center/common row. It would have been best to preserve the red/green color scheme,