Full Version: A Swing Bridge instead of a Duck Under
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Tired (or getting too old) to duck under??? Build a swing bridge to gain access to your layout's "innards" Smile

This bridge was adapted from a Model Railroader Magazine "HO Scale" articla from the early 2000's, but I cant find it anymore.

The Problem: I hurt my back years ago and now it really is a bad thing to "Duck". The MF&W RR has a section of "Air Space" about 30 - 40 inches wide and about 4 ft long that I have to get the trains across, since I can't get the time to teach them how to jump canyons. Eek Nope

One solution -- a "Drop in bridge" - you build it & put supports at either end - lay it down there & lay your track & scenery... Then when all the surrounding scenery is completed & you take said bridge up...where do you put it??? I have one already that just leans against the layout. Adding a second would be just too much.

Second Solution: A swing bridge - it stays attached to the framework, and "Swings " out of the way for access to your layout for operating, cleaning, building etc.... whatever you need to do, that cannot be reached from the edge of the layout.

Here's the finished bridge. Note the hinges on the left.
Now - how did I get there??? About 4 hours work. First - The bridge was designed in MRR Mag - to be for 2 HO tracks The "Base" is a 1 X 6 (Actually 3/4" X 5-1/2") but it works nicely for G. It would work well for O Scales as well as HO. Not too sure about the alignment of N, but you could experiment to see if it could work.
As far as construction details this is where it gets "potentially abstract"!

Your bridge will be custom made for your layout, your height - your width and your length. Yes, you can build this any width, want to run 1 N gauge track, or 1 HO?? Make it the width of the 2 X 4 support, heck just use the 2X4 for the base. A 2 X 4 is nominally 1-1/2 X 3-1/2 you can definitely fit 1 single track on 3-1/2". But remember you can also turn the 2 X 4 vertically and use the 2" side.. (Nominally 1-1/2" Smile

You just have to decide what is best for your layout.
Notice in the above picture - The Horizontal 2 X 4 does NOT go the entire length - It leaves a space for the support that is attached to the end of the layout.. Also notice the small "Shim" stuck to the bottom of the 1 X 6. This is for aligning the tracks when the bridge is closed.

Rear View:
The 45 degree support board is so you can lean a bit on the bridge - without affecting the ability to close... The vertical black 2 X 4 is the "Hinge Side" and connects to the end of the layout - where you have to put a second 2 X 4 to give you the "base" hinge attachment. So after adding a "Frame" 2 X4 and the second bridge 2X4, you will have the vertical part of the bridge complete.

Note - this will be explained in detail later... Don't get confused... yet! Goldth Goldth Goldth
Here is the hinge side.. Note the double 2 X 4 on the layout - to be able to attach the hinges & also the wires. If you want to have a swing bridge, you have to give it power too.

Also note "the Top Hinge" is about 3" below the top. All you can see on this side is the "Pivot" but it's there.
ok - enough "background stuff" Lets get busy!!!
The height of the vertical 2 X 4 should be:

The height of the layout (minus) 1" for floor clearance (Minus) the thickness of the support "base board" (1 X 6 = 3/4 thickness

Got that???

So, you measure floor to height of benchwork... 36" and you are using a 1X6 (take away 3/4")
don't forget the "Bottom Clearance"..... ( take away another 1")

36 - 1 = 35............ 35 - 3/4 = 34 -1/4

34 - 1/4" is the length of that vertical 2 X 4. Why so long? You want it as long as possible for weight distribution. The 45 degree angle will be supporting the track and it must stay as level as possible, so it will align with the "other end" of the opening (Track).
Now for the horizontal support:

Look at the pic below. You have full weight support on the hinge side, but the other end "floats" in space.

You need an "Alignment Block" (shown below) at the other end of the layout "Permanently & Securely" attached!! This can't move!!! Did I say it plainly enough??? It CAN'T Move!!!! -- Why?? because "If" it moves, when you go to close the bridge - your rails will be Mis-aligned!! Eek Eek

......................can you say "trains on the floor"!!! Eek Shoot
This bridge has lasted on my layout for over 6 years with very minor adjustments being made. I really can't believe how sturdy this is. Big Grin

In G - I have 1 mm to mess with Is that wider than an N rail??????

Also look at that picture & notice the "triangular 3/4" piece of wood (Blue Arrow). It's the "Cutoff" from the 1 X 6. It is permanently & Securely attached. This acts as a "stop" for the bridge when it closes and also aligns the railheads.

You will also note the "Pressure switch" (Green Arrow) and the "Throw Bolt" (Red Arrow) - The switch is wired to the power side of the tracks and is Normally Open. The tracks have insulators on the Power side - 2 feet on either side of the bridge. That way - "if" you don't have the tracks aligned - no train can "fly off into the sunset"! Shoot

........... and as stated elsewhere - all couplers will work perfectly as the train flies off the layout taking the engine and as many cars as "Murphy" sees fit. Eek
Now... With all this in mind. You determine the length of that horizontal support this way:

First - take a 2 X 4 & cut off a 4" piece. This becomes that Alignment Block above.

The horizontal support is the length of the "open area" (minus) 6" (clearance for the 2-1/2" block and that throw bolt plus clearance for the "vertical" 2 X 4 on the hinge side).

Attach that Alignment block now... As shown above - it should be 3/4" below the level of the layout. (Thickness of the 1 X 6)

So if your open area is 36"...... The length should be 36 - 6= 30" for the length of the Horizontal 2 X 4.

Now - you have the vertical & horizontal finished.. Screw them together as shown in the detail shot below (red Arrow points to the attached area). Make sure they are at right angles. - Use a square if you have to.

For the 45 deg support board (2 X 4), I measured from the top of the hinge board 15" and then horizontally - the same 15" (see below).

I made marks & then holding a 2 X 4 against these marks - I marked the new 2 X 4 along the inside edges so I could cut the support board & it would be a 45 degree cut.
Then drill it & attach it to the other supports. It should be attached to the boards at the 15" marks. This should give you a perfect 45, 45, 90 triangle. it should also "Level out" the horizontal 2 X 4.

If you want to put a facade on the front as I did, get a piece of 1/4" plywood or other wood & lay the frame on top of this new triangle and mark the cuts so you can fit it on the triangle - to make it look nice. (this step is optional)

The board is attached to the front, but here's a rear view - showing the plywood through the frame.
ok - now we have the frame completed, time to attach it & run

Attach a 2X4 to the side of the layout as shown below. Screw the hinges to the 2 X 4.
If you have a leg you can build on, like I did - build onto it.

I just used a second 2 x 4 as shown then attached the vertical "bridge" 2 X 4 to that - ending up with 4 2 X 4's counting the layout's leg. Notice I Had to make a cut out on the 1/4" plywood for the top hinge.
Now - you can attach the bridge. Place the framework in the opening.

If you are using the Horizontal 2 X 4 as the base - you should have the 2 X 4 even with the layout height.

If not; set the height 3/4" (Thickness of 1 X6) below the level of the layout. You can use scrap wood under the vertical support to rest it on. line the vertical 2 X 4 up with the support and screw ONE SCREW through the top hinge. This will take the weight off and let you let go so you can align everything. Put a second screw through the top hole of the bottom hinge.

It should swing out very smoothly and you should have a space between the end of the horizontal 2 X 4 and that alignment block.

Open it & get the 1 X 6 and cut it to the length of the opening above the closed bridge:
Lay it on the layout edges, across the opening, and mark it underneath, along the edge of each end of the layout. "cut it right along these lines"...

This will give you a board that should drop right in and lay on the frame you built (close the bridge again). It should fit just a bit loose. When you drop it in - inspect BOTH ends - this new board should be level with both ends of the layout.

It should be a smooth transition from bridge to layout on both ends. If it is - You re fine - if not - you will have to raise up either end of the layout with shims under the legs or re-attach the hinges. Remember - you can also glue a shim to the bottom of the 1 X 6 at the "Opening" end as I did above.

Once you have it level - Attach it to that horizontal support 2 X 4 with screws. Then screw the rest of the hinge screws in. AFTER you have attached and aligned the 1 X 6 again!!!!!

Then try to open it.. It won't open - because you need to cut it.. Get a wood saw - or hack saw (takes longer)..and cut as shown below. (red line).
The cut should begin about 1 - 1/2 inches from the end of the 1 x 6 at a 60 degree angle. Notice the side of my bridge (top) ends at the cut. You are beginning to cut that triangle you saw earlier & through the 1 X 6 NO Further - as evidenced by the cut mark in the layout

Just mark it with the saw blade for now.

When you have a "good mark" in the 1 x 6 - lift it above the layout - just lift the end of the bridge enough to clear the layout & open it. Now saw the end off. you can use any powered saw now.. I used the jig saw.

When you cut off that triangle... Pick it up, close the bridge again & lay that triangle in the empty space. MAKE SURE everything fits tight!! And again - check the levels and easements at this end of the bridge. ~~~~ Everything look good????? ...... Your ok then.

Open the bridge again & put the triangle down on the bridge so you wont lose it

Now - the throw bolt... Mount the throw bolt by closing it & swing the lock over as above.... The top of the bar should be "just below the height of the layout" The object here is to lock the bridge straight - but not interfere with the track on the bridge. Here's that pic again for reference:
When you have it mounted - open the bolt (it should drop down) -- close the bridge tightly again - Press down on the bridge and Hit the bolt with a hammer, from underneath, to make a mark on the bottom of the bridge.

Drill a 1/8 hole straight up through the 1 x 6 at the center of the mark. drill as straight (vertical) as you can.

When you have done that - drill a vertical hole down through the 1 X 6 (using the small hole as a guide) the Exact diameter of the bolt bar.
Here's a view of the finished hole and a detail view of the "Paint paddle" I used for a shim.:
Now, close the bridge (again) & push the bolt up through the hole & lock it - Everything should be nice & tight - no movement.. What's that?? it moves a bit???

Pick up that triangle and pull on the bridge (it wont open because of the bolt) - put the triangle back in the open area & push it against the bridge... Now the bridge should stay tight. I can shake my layout by "shaking" the bridge.

Pre-drill a hole in the triangle & through the support block & screw it into place. BE CAREFUL NOT TO SPLIT THE BLOCK!!!!!

Now when you close the bridge against that triangle, the hole should line up with the bolt & you can push the bolt through the bridge bottom & lock it tightly.
Fancy stuff?? Roadbed?? Anything you want, add on now.. Make it your own work!! Be creative.

I decided to make it a "Wood Bridge". See the dark green patch under the track leading to the bridge?? It's a wooden shingle shim, used to align the approach to the bridge.
Well - you're finished!!

Close & lock the bridge. Lay your track and where the track crosses the "cut you made" take extra nails & fasten every tie on both sides of the cut.. 4 or 6 on each side of the cut... Think about power supply here - attach a wire to each rail here - the wire should be long enough to go to the hinge end of the layout plus 1 foot.

Fasten nails at the other end, same thing 4 or 6 inches on either side of the end of the 1 X 6 - Where the bridge meets the layout.

Then take a hack saw and sloooooooooooLY evenly, carefully.... cut through the rails & the ties & the roadbed.. the same exact angle and right above your previous cut.
Finished cut on tracks:
This pic also shows the wires.

Then cut the other end - same thing - along the break from bridge to layout.

When you're done here - Unlock & open the bridge SLOWLY!!!!! Look at the ends of the rails making sure they don't bind!!! If they do - you'll have to sand them down a tiny bit (Dremel tool)

If they don't bind - you're done!!! Close that stinker!! Run a car or 2 over the bridge just to make sure those rails are perfect.
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