Saturday, May 7, 2016

Electrical wars: Part 9: contacts for a turnout

Nearly all the turnouts on my layout are hand-thrown, and most rely on point-to-stock-rail contact for electrical continuity of the route through the turnout. In almost all cases, this works all right, with some need before each operating session to carefully clean that contact area where the points and stock rails touch. But in a few cases, contact is stubbornly bad, or worse, bad sometimes and fine other times. This post is about one solution to the problem, without resorting to a switch machine.
     I should mention that I prefer hand throws on other than mainline switches, because that was how the prototype worked. Naturally a turnout far from the edge of the layout, that would require a long reach among structures and other scenery, to operate a hand throw, is an obvious choice to operate with a switch machine, but other than that, I want to retain hand throws as much as I can. I am gradually changing over my old Caboose Industries “giant” ground throws to the smaller and better operating Bitter Creek ground throws (see my post evaluating these ground throws at: ).
     In the post just cited, I also discussed adding electrical contacts to ensure reliable behavior of a turnout, in that case alongside the track but concealed inside a structure. But one does not always have a handy location for such a concealing structure. Instead, the contacts have to be placed underneath the layout. This post shows how I did that recently for one of my problem turnouts. But the challenge was, the turnout is already installed and ballasted. There was no hole beneath the throw rod for an operating rod to contacts underneath.
     Creating that hole seemed like the first order of business. As I have done in other such cases, I first drilled a hole a ways from the location of the throw bar, 2-3/4 inches to be precise.

Afterward, the hole was easily plugged with some Sculptamold and a little ballast.
     Next, I could clamber under the layout and carefully measure 2-3/4 inches from the initial hole, thus hopefully locating the center of the throw rod, and then carefully drill upward, watching the chips fall from the drill bit. First they were plywood, then Homasote, then a bit of cork (I had used cork roadbed in this part of the layout). Now I knew I was up to the layout surface, while avoiding drilling up into the throwbar. The hole was fairly small diameter (same as the one shown above), so I enlarged it with a 1/4-inch drill bit, being careful again not to drill into the throw bar above.
     Now I was ready to assemble the various parts of the arrangement. First of all, I needed a set of contacts. This is easy in my case, because some of the twin-coil switch machines used on my previous layout had been replaced due to inconsistent performance, and I could harvest the nice contacts provided on them. Here is a photo of the elderly Kemtron machine I cannibalized (written on it is “bind,” which is why it was surplus):

Part of the machine can be disassembled by removing the screws that hold it together, but the pivot at left is riveted, so I had to use a hacksaw and cut off one end of the machine base, then cut underneath the contacts. When that was done, and the cuts filed clean, I had the part shown below.

The cut edge is toward the lower right. The mild steel plate here is all one piece, and was kept because it also mounts the contacts.
     There also has to be a pivot plate to provide a positive motion of the bottom of the operating rod in response to hand-throwing the turnout above. This plate can be a simple square of brass sheet, with a hole suitable for the operating rod. I fumbled around in my materials box and found some thin brass sheet, and drilled a hole in it for the “music wire” I chose for an operating rod. Here is a view of the plate, installed with a single screw, covering the hole drilled up to the throw bar. Actual size of the brass piece is about 1/4 x 3/8 inches, obviously not critical dimensions. The hole is a bit larger than the diameter of the operating rod.

     The contact installation described above ended up in a narrow corner, which I just can’t seem to photograph clearly. Accordingly, I will show a nearby one of the same type, though with a different set of contacts. I particularly wanted to show the end of the operating rod, which shows better in the alternative one I photographed. The end of the operating rod seems to get bent to a little different shape in every installation like this, because I just do what seems best at the time. Below is a clear photo of that nearby installation, with the rod slipped through a hole in the center of a trio of contact arms. (You may click to enlarge.)

In this view, the red and green wires at the bottom of the photo are not part of the contact installation; the other wires are the track feeders connected to the contacts.
     This kind of contact installation allows the turnout on the layout to still be thrown by hand, but ensures good electrical power to the frog and point rails. My new installation seems to be working correctly (touch wood), and it will be an improvement if it remains solid.
Tony Thompson

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