Bridging the Gap

The benchwork is coming along nicely.  There is almost 60 feet of L-girder framework erected now.  Hopefully I’ll get another 23 foot section done this weekend.

One of the construction tasks is going to be the fabrication of a bridge section to span the doorway into the room.  I’ve been thinking about this for quite some time and had briefly thought about several different options: a swing-up section, a lift-out section, a lift-up section, a swing-down arrangement, and a swing gate.

I dismissed the swing-up section (a bridge hinged on one end) because the 4 foot length of the bridge is too tall and would hit the ceiling.  Then I dismissed the lift-out because of the inconvenience of lifting out, then storing the section.  The lift-up section (the entire bridge rising vertically) seemed outlandish.  I really didn’t think much at all about the swing-down approach (another bridge with a hinge on one end); it just didn’t seem sexy.   I finally settled on the swing gate.

Now I started planning what the bridge would actually become.  I decided early on that I wanted a low lying tract of land coming out of Monterey that would feature the track crossing over a marshy area on a long, low timber trestle.  The only place such a trestle seemed to fit in the trackplan was (you guessed it) right at the point where the track goes past the doorway into the room.  I finally decided that to model the trestle in this location I would have to build essentially a box with a depressed area in its top.  The box would be about 4 feet long, 12 inches wide and likely about 8 inches deep.  I figured the bridge would normally be open, but wanted the bridge to be capable of functioning as a duck under during a session.  As the design developed (and after studying every swing gate I could find on the internet), I concluded that trying to support such a bridge with a hinge or two on the side of one end would likely not work very well in the long term; there would likely be too much twisting and wracking in such a design.  So then I added structure to the bottom of the box to essentially make something more like a Dutch door.  Of course then I lost the possibility of a duck under.

But there was another problem bugging me.  There are five wall switches for lights and receptacles located right next to the door opening.  Going straight across the doorway with the bridge section would have had benchwork blocking several of the switches.  Hence, the bridged section is at an angle as it crosses the doorway (see trackplan on the website), allowing access to the switches.  With this configuration, there is an angled section of benchwork poking out to start the bridged area.  Because of this, and my desire to keep curved track off the swing section, I found that the required hinge point would not allow the bridge to pivot and come to rest flat against the layout when open.  It would instead be sticking out into the aisle, partially obstructing it.  I was becoming unhappy with the swing gate concept.

Next up was another review of the vertical lift bridge (the lift-up section).  I had seen something along that line on Charlie Comstock’s Bear Creek and South Jackson.  He uses that idea to provide an access pop-up on his layout.  It uses a pair of drawer glides oriented vertically and seemed simple enough to build.  I figured I could build a beefier version of this as a bridge.  Then a few weeks ago while erecting the first benchwork sections, a thought occurred (sound of hand slapping forehead).  There is insufficient clearance over this section of layout for a raised bridge due to the lighting valence passing overhead.  Bam!  Idea dead!

So that leads me to my latest thoughts: the swing-down section.  Wayne Robichaux had suggested this so I did a couple quick sketches, and it seems like the idea may be better than I first thought.  By using a rod within some bearings (something akin to an axle), and placing it an inch or so down and inboard of the bridge-box, the thing would swing down nicely and would tuck up under the layout when down.  My next thoughts are ways to latch it in the up position, and whether it will need assist in the lifting operation.  For the latter, I’ll have to figure out how much the thing will weigh, which will probably require me to at least gather some materials of the approximate size required to build the bridge-box.  Once I know the weight, I can more reasonably come up with a design for these other tasks.

So that is where I’m at.  I would like to figure all this out early on, as this bridge is essential to even the earliest operation of the layout . . . Monterey is inaccessible without this bridge.

Got any other ideas?  Comments are welcome.

-Jack

4 thoughts on “Bridging the Gap

  1. Jack
    I hope to eventually add either a drop down or lift up section accross a doorway to add a log branch. I figured that one of those door bolt devices to secure the lift out section (and hold it up if I go for a lift up) and also to align the bridge with the main benchwork. Mine won’t be as long but I still figure on attaching handles to lift it.
    I imagine that a four foot section, heavy enough to resist warping or bending would be quite heavy. A counter balance weight or maybe even a motorized lift cable might be needed.
    Maybe a metal bridge would be better (lighter) than plywood or other wood
    Bill

  2. P. S. On the door bolt idea, you definately want to install it to get a good tight fit and only then lay the track. I would lay one piece over the gap and then cut it. Also, putting a re-railer track on both sides of the gap will greatly reduce (hopefully eliminate) derailments. I use these re-railers at each end of each level on my elevator and on the main benchwork. Works great.

  3. Art,

    Since I don’t have the layout built yet, I can’t add pictures! However, if you visit the website, go to the trackplan. The bridge section is currently shown on the plan as a swing section and it’s crossing by the door into the room.

    As of this writing, I’m encouraged by some of the sketches I’ve done (in CAD). The actual swing down part of the bridge I think would work well. I want to spend more time thinking about the latching mechanism, and whether the bridge will need mechanical assist in lifting it up in position.

    -Jack

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