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 Posted - June 15 2017 : 8:03:53 PM
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There are lots of track plans for Atlas Snap Switches and their clones, and my layout uses a fair amount of that geometry. The switches are not top of the line, though, and they have potential problems. I was preparing a switch to be installed on my layout and photographed some of the changes, in case others might find them useful.
The first problem:
One of the switch points is lower than the stock rail it touches. This allows the outside edge of the wheel to be pushed inward by the inside edge of the rail, causing a derailment. This is especially true of 2-wheel pilot trucks on heavy steam engines.
Also, the switch point is a bit blunt on the end allowing flanges to pick the points and run behind them instead of along them.
This may be solved by filing the ends of the point to a bevel that kicks the flange to the correct side of the point, filing the sharp inside corner of the head of the stock rail to allow the outside edge of the wheel to climb up, and by adding a shim under the point:
The file in the picture is called a riffler file and allows you to file down between the rails or in other confined spaces.
The next problem: The closure rail does not line up with the switch point:
The closure rail just did not follow the curve, but straightened out at the end, missing the point. I bent it inward to meet the back of the point. There was room to do this, since the gauge was pretty wide, there, anyway.
Here's a shot showing the fixes around the points:
The pictures don't show it, but the stock rail is beveled a little on the inside edge where the outside edge of a wheel would roll up onto it from the point.
While we're looking at this end of the point, a tiny bit of automatic transmission fluid pulled under the rivets by capillary action will protect an electrical contact from corrosion and contamination.
Meanwhile, back at the frog, another potential problem lurks:
The flange ways between the guard rails and the running rails are too wide. The inside surface of the wheel flanges should run alongside the inside of the guard rail, pulling the opposite wheel along the correct side of the frog. These switches are made to accommodate most any huge oversize flange, but on normal flanges, they have no effect and the wheels can pick the frog and run up over it instead of along the correct side.
I glued a shim along the inside of the guard rail. I left the flange ways a little wider than the NMRA standard, so I could use equipment with somewhat nonstandard flanges, but I narrowed it down some to prevent most, if not all, of the frog picking.
The shim is a plastic strip .060" top to bottom and maybe about .025" thick. The matches are just nice wedges to hold the shim in place as the glue dries. The alligator clips hold the end of the shim to the guard rail where it funnels into the flange way. If your shim is too thick, after the fact, you can whittle it down some with a nail file.
I dulled down the shim and the sides of the rails with Neolube, a thin graphite paint.
Here's the finished switch with all the changes:
Carpe Manana!
Edited by - scsshaggy on June 15 2017 8:08:22 PM
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Posted - June 15 2017 : 8:32:00 PM
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points is what a switch is called in England
good tips thanks 
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Posted - June 15 2017 : 9:38:54 PM
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Some good information, thanks. And a pretty decent macro lens, too.
“There are a thousand things that can happen when you go light a rocket engine, and only one of them is good.” — Tom Mueller, SpaceX, 2012
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Posted - June 16 2017 : 10:40:20 AM
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Quite a study. I've had all these problems, but never knew
exactly where the issue was, now I see this very differently.
Hopefully I can put some of this to work on the Tycomania VII.
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