13th Feb 2018, 02:17 PM
The Big U Lift Bridge
At our last show we were lamenting how our club lift bridge didn't work so well anymore. We know it's at least 15 years old, probably closer to 20, so we really can't complain. However, it got me to thinking about a "better" design. Our current one simply clamps to the modules on each side, which means if the layout has any pressure on one side it can be a bit difficult to close. That's part of why it took some abuse.
I drew this up as a result in SketchUp.
The idea is that the two sides are cut from a single sheet of plywood in a big "U" shape. This provides continuous support when the bridge is open, so they layout can't move around. I've left out two boards so you can see the construction, the bottom cover (that you would step on) and the inside vertical cover on one side (identical to the one on the other side).
Additional U shaped braces are cut and installed inside on the bottom so the thin bottom (3" tall, 1" off the ground, 4" step total) has more support. The panels that affix to other modules have slots cut in them so the clamps can be moved up and down to optimal position for maximum clamping force. What look like 45 degree cuts on the sides of the top are actually more like 42 degree, so when open the bridge goes just past 90 degrees before resting on them so it will remain open on its own. The base is 1' wide to provide more clamping area and stability, while the lift bridge itself is 7" wide. All parts are cut from 3/4" plywood, it almost all can come from a single sheet but it takes a few inches of a second sheet to make some of the U braces. Note that when closed there is a block under the hinge side, and it closes on the supports on the latch side, so it can't "sag".
The only exception is the alignment piece on the bottom of the lift up part. That would be 3/4" hardwood of some sort so it could be sanded into a taper to help with alignment.
N-Trak bus (12ga w/powerpoles) would run down and under. There would be three feeder drops, one on each fixed section, and one on the lift up section. Feeders on the lift up would be as close to the hinge as practical, and the wires would simply be exposed on the bottom for a very short run.
I would probably finish as if it were furniture, stain and poly, or maybe even varnish. The tracks would get ballasted between the uprights to make it a bit more visually appealing than many bridges.
4 pinball leg levelers would be installed. They can hold up a 400lbs pinball machine, so even if someone stood on it they should be fine to support the weight.
This is obviously larger (to transport) and heavier (I estimate about 50-60lbs) than most of the collapsable bridges I've seen clubs use. But unlike the collapsable bridges it's weight and stiffness means the layout should move less, and it could be used next to corners or other less-stable modules without trouble.
I welcome comments though before I go commit saw blade to plywood. I know there are plenty of folks on here who have built modules and may have thoughts. My current thinking is to build a prototype for my home layout (I finally have a loop of my own modules in the basement!) and then see if my club has any interest in a duplicate. Right now many are skeptical due to the weight and size, but I think while it will be a little more difficult to set up it will be trouble free during the show. Our current bridge has to be fidgeted with every opening, which is a lot less fun. Feel free to even say I'm crazy, if you really think it's a bad idea. I want honest feedback!
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13th Feb 2018, 07:41 PM