M&K Junction Railroad

M&K Junction Railroad
Another train of eastbound coal crosses the Cheat River

Wednesday, June 15, 2011

A Few Simple Solutions

Mounting Tortoise Switch Machines

When I first started building this layout, I had to put in 3 single crossovers, requiring 6 switch machines. I spent a considerable amount of time under the layout affixing switch machines - and bumping my head. Now that I'm working on the yard ladder into hidden staging and I've come up with a simple and obvious way to attach switch machines without all of the hassles.

The problem with attaching the Tortoise machines is that the built-in mounting ears are too close to the machine to reach easily with a screwdriver. Plus the machine is small and it's hard to position it critically and drive the screws without pushing the machine out of place. To alleviate these problems I've attached each Tortoise machine to a scrap of plywood. The size of the plywood is not important so long as it extends well past the machine proper. The plywood is, in turn, mounted to the underside of the layout. The plywood forms a 'handle' that makes it easy to position and screw the machine in place without movement.

These photos should be self-explanatory.

You'll notice in the pictures above that the actuation mechanism of the Tortoise machine simply extends past one edge of the plywood mounting plate. In this way it is not necessary to drill a hole for the actuation wire through the mounting plate. Also note that I have pre-drilled and countersunk holes for the mounting screws. Four holes are not really necessary, but it provides some flexibility in where the mounting screws will be driven. The combined thickness of the mounting plate, subroadbed (plywood) and roadbed (cork and foam) is well over 1". This would be too thick if I were using the music wire actuator that comes with the Tortoise; but I am already replacing the actuator with heavier wire, so I simply cut this wire longer.

In O Scale a #6 switch is approx 18 inches long and track center-to-center spacing is typically about 4"; so switches cannot be densely packed and there is plenty of room under the table for these oversize plywood mounting plates. In the smaller scales, this approach may not be possible.

Mounting Servos as Switch Machines

I'm taking the opportunity of motorizing all of the switches in hidden staging to experiment with servos as switch machines. While I will eventually experiment with the servo actuators from Tam Valley Depot and Duncan Mcree, I currently have an ESU stationary DCC decoder that drives servos. To use the decoder that I have I had to buy a servo at the local hobby shop (ouch!) rather than pay less and wait for it to arrive via mail-order. How to mount the servo was a problem. After thinking about it for a while, I decided on the following technique. I simply glued the servo to a right angle bracket sold in home centers for building decks.

The bracket is Simpson 'Strong Tie' A21Z, note: this is the right angle bracket with one arm longer than the other, that's the arm that the servo is glued to. I used Gorilla Glue to attach the servo. I roughed-up the bracket and servo with sandpaper before I dampened the bracket with water and applied a THIN coat of the glue to the servo, then clamped the two together. Since I used a thin coat, this time the glue did not foam up all over the place; I've finally found a use for Gorilla Glue.

Here's the servo switch machine installed:

For fitting the actuator arm, made of music wire, to the servo crank I came up with what I think is a novel solution which you can see here:

I bent a length of wire into the shape above. The length of the straight section to the right should be enough to reach up through the subroadbed, roadbed and through the throw bar on your turnout. If in doubt, make it longer, any excess can be cut off after installation. The form of the wire on the other end is shown in the detail close up here:

The distance between the bends should match the hole spacing on two opposite arms of the servo crank so that it fits like this:

In case it's not obvious how to get the bent wire into the servo crank, here's a short video on how it's done:

The self-retention feature that you see in the video works because I am using relatively stiff 0.039 wire as a actuation arm. That allows the right angle bend at the end to exert enough outward pressure to hold the arm in place. If you use significantly thinner wire this might not be the case.


  1. Just wondering if you think Silicone might work for fastening the Servo to the metal bracket? If not what else would work well that is readily available at the local hardware store?

  2. Good article on the new technology with points and Features but give more information in the next article.Keep up the good work.