Manual Switch Throws
Manual Switch Throws
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Manual switch throws located near the turnouts they operate are a natural with walk around control. The ones shown here lock the points and have electrical contacts for powering the frog and for operating signals.  figure 1 These Double Pole Double Throw (DPDT) slide switches operate turnouts via piano wire links between their handles and the throw bars of the turnouts. Each link includes a kink or a one turn spring which makes up the difference in throw between the slide switch and the turnout. The slide switch end of the piano wire is soldered into a short length of 1/16" OD brass tubing which in turn is expoxied into a hole drilled in the slide switch handle. This eliminates slippage at this point and provides a means of adjustment - melting the solder and repositioning the piano wire. The slide switches are aligned with the turnouts they operate for quick identification. Sometimes, as with the pair shown, the slide switches and their turnouts are so close together that additional identification is used - in this case, one handle is painted silver and the corresponding throw bar is also marked with a dab of silver. The slide switches are mounted in simple hardwood blocks which in turn are mounted on the layout fascia. Perhaps mounting the slide switches under the table and using just a push rod through the fascia would be more elegant, but this surface mounting allows operators to immediately locate the throws and determine their positions. Electrical wires run through the face behind the slide
switches.
One half of each slide switch is used as a Single Pole Single Throw
(SPST)
switch to back up the point contacts of the turnout frog, or in the
case
of turnouts modified for DCC, to power the frog. The other half
of
each slide switch is used as another SPST switch to control signals.
My personal favourite, but more time consuming to make, it this switch throw based on a toggle switch mounted under the table. As the toggles are free to rotate on most toggle switches, one end of a piano wire "lever" is fixed to the bracket on which the toggle switch is mounted. The other end of the piano wire extends through a hole in the turnout throwbar. In this way, the points are positively locked by the toggle switch when it is thrown. A little bit of geometry or a good drawing is necessary to locate the hole in the toggle. Its position depends on the length of the bracket, the thickness of the table top or road bed, and the characteristics of the toggle switch and the turnout. When doing the calculations or drawing, allow about 10% over travel, which will be taken up by the piano wire lever. The toggle switch is operated from the front of the layout by means of a push rod. What makes this manual throw superior to simpler ones based on slide switches is the length of throw. A little bit more geometry will show exactly how much the toggle has to be extended for a particular length of throw. I like about a one inch throw, which is a much more positive indication of switch position than the 1/8" or so of a slide switch. In figure 2, the toggle was extended by tapping in a brass #4-40 x 1-1/2" machine screw. In other similar manual throws, the a hole was drilled for the machine screw and it was soldered in place. The 1/8" diameter push rod is attached to the machine screw by soldering it inside a length of 1/8" ID brass tubing, then flattening and drilling the end of the tubing. The flattened end fits loosely between the head of the machine screw and a brass nut, which is later soldered in place, as can be seen in figure 2.
Some knobs that control switch throws using toggle switches
are shown
in figure 3. There is no doubt about whether the know is pushed
in
or pulled out. In this particular application, white knobs
control
turnouts in the engine yard, grey knobs control turnouts in the
classification
yard, and gold knobs (not shown) control turnouts on the main line.
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