# Swing Bridge Construction

Discussion in 'The Academy' started by N Gauger, Jan 1, 2005.

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1. ### N Gauger1:20.3 Train Addict

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Well - I finally got a round to taking these pics for the details.......
This bridge was taken from a Model Railroader Magazine, but I cant find it anymore

The Problem.... Don't want a duck under.... Have a section of "Air Space" about 30 - 40 inches wide, that you want to run track across, because you haven't had the chance to teach your trains to jump canyons.

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???

Solution 2....... A swing bridge - it stays attached to the framework, and "Swings " out of the way for access to your layouts "innards"

Here's the finished thing

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2. ### N Gauger1:20.3 Train Addict

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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 & HO as shown below.

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3. ### N Gauger1:20.3 Train Addict

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As far as 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 definatly fit 1 single track on 3-1/2"

Here is the details view:

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4. ### N Gauger1:20.3 Train Addict

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Notice in the above picture - The Horizontal 2 X 4 does NOT go the entire length - It leaves a end space for the support that is attached to the end of the layout..

The 45 degree support board is so you can lean a bit on the bridge - without affecting the ability to close... The vertical 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.
5. ### N Gauger1:20.3 Train Addict

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Here is the hinge side.. Note the double 2 X 4 on the layout - to be able to attach the hinges too & 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 base. All you can see on this side is the "Pivot" but it's there

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6. ### N Gauger1:20.3 Train Addict

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ok - enough "background stuff" Lets get busy!!!

Here is the support structure!

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7. ### N Gauger1:20.3 Train Addict

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The height of the "Right Hand" vertical 2 X 4 should be:

The height of the layout - (1" for floor clearance) - (the height of the "Base" 1X6 (3/4") )
Got that???

So, you measure floor to height of benchwork... 36"
you are using a 1X6 (take away 3/4")
dont forget the "Bottom Clearance..... ( take away 1")

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

34 - 1/4" is the length of that vertical "Hinge Support"
8. ### N Gauger1:20.3 Train Addict

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Now the horizontal support

Look at the pic below. You have full support on the hinge side, but the other end "floats" in space You need an "Alignment Block" at the other end of the layout "Permanantly & Securly" attached!! This can't move!!!

Did I say it clear?? It CAN'T Move!!!! -- Why?? because "If" it moves, when you go to close the bridge - your N or HO rails will be Mis-aligned

......................can you say "trains on the floor"!!!

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

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9. ### N Gauger1:20.3 Train Addict

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Also look at that piccy & notice the "triangular 3/4" piece of wood It's the "Cutoff" from the 1 X 6 that you will note in the second pic (HO Track) - is missing Go look - I'll wait

It is permantly & Securly attached.. see the "Divot" It's one of the pre-drilled & Countersunk screws (the other is under the track)

This acts as a "stop" for the bridge when it closes

You will also note the "Pressure switch" and the "Throw Bolt" - 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 dont have the tracks aligned - no train can "fly off into the sunset" Ouch ouch ouch!!!!!!

........... and as stated elsewhere - all couplers will work perfectly as the train flies off the layout
10. ### N Gauger1:20.3 Train Addict

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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" - 6 (clearance for the 2-1/2" block and that throw bolt plus clearance for the "hinge 2 X 4"). Attach that Alignment block now... As shown above - it should be 3/4" below the level of the layout.

So if your open area is 36"...... The length should be 36 - 6= 30"

now - you have the vertical & horizontal finished.. Screw them together as shown in the detail shot below. Make sure they are at right angles

Now, you have to decide where you want to put that 45 deg support board (2 X 4)

I measured from the top of the hinge board 15" and then horizontally - the same 15". 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.

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11. ### N Gauger1:20.3 Train Addict

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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

Then, get a piece of 1/4" plywood or other wood & lay the frame on top of it & mark the cuts so you can place 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.

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12. ### N Gauger1:20.3 Train Addict

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ok - now we have the frame completed, time to attach it & run

Screw the hinges to the 2 X 4 you already attached to the layout... Oops - Did I skip that???

Cut another 2 X 4 the same length as the Vertical support & screw it to the framework of the layout - if you have a leg you can build on - use smaller peices of 2 X 4 to build onto & space out the "main 2 X 4" so you can attach the hinges to it. I just used a second 2 x 4 as shown below - then attached the main 2 X 4 to it - ending up with 4 2 X 4's counting the bridge's hinges

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13. ### N Gauger1:20.3 Train Addict

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So above - you can see (from left to right)
The Vertical support
the hinge support
the spacer
and finally - the Leg of the layout Framework.
14. ### N Gauger1:20.3 Train Addict

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After you get the hinge support mounted, attach the hinges to it - evenly space them.

Now - you can attach the framework. place the framework in the opening

If you decided to use the 2 X 4 as your base - you should have the 2 X 4 even with the layout height - if not - set the height 3/4" below the level of the layout. You can use scrap wood under the vertical support to rest it on. Screw the hinges to it.

It should swing out very smoothly after you get all the screws in & you should have a space between the end & that alignment block.

Open it & get the "bed" frame Board - The 1 X 6 & cut it to the length of the opening above the closed bridge... Lay it on the layout ends & mark it underneath, along the edge of both ends. "cut it right along these lines"...

This will give you a board that should drop right in & lay on the frame you built. 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.

Once you have it level - Attach it to that support frame with screws.

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.

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15. ### N Gauger1:20.3 Train Addict

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Cut it at a 60 deg 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 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!! Close the bridge tight - check the alignment again.... and seat the traingle against the rear of the bridge.. Everything look good?????

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.

When you have it mounted - open the bolt (it should drop down) -- close the bridge tightly again & Hit the bolt with a hammer 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 as you can

When you have done that - drill a hole down through the 1 X 6 (using the small hole as a guide) the Exact diameter of the bolt bar

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 - Pre-drill a hole in the triangle & through the support block & screw it into place. Now when you close the bridge against that tringle, the hole should line up with tha bolt & you can push the bolt through the bridge bottom & lock it.
16. ### N Gauger1:20.3 Train Addict

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Side panels??? I was going to leave the sides off, but thought it looked better as a "girder bridge", so I made some sides out of 1 X 3's - you can use anything.

Plexiglass would be better just remember if you do use 3/4 thick wood.. You have to cut out a bit at the end so it will open wider. otherwise it hits the layout & wont open all the way - see below.

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17. ### N Gauger1:20.3 Train Addict

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Well - you're finished!!

Close & lock the bridge. Lay your track & 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.

Do the same for the other end. 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.

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

When you done here - Unlock & open the bridge SLOWLY!!!!! Look at the ends of the rails making sure they dont bind!!! If they do - you'll have to sand them down a tiny bit (Dremel tool)

If they don't bind - you're done!!! Clost that stinker!! Run a car or 2 over the bridge just to make sure those rails are perfect.
18. ### N Gauger1:20.3 Train Addict

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Now - Electrical Here you have an option. If you are confident that you will never run a train over the open bridge - then just attach the wires from the bridge rails to your lead track on the hinge side. Make sure you attach the right wire to the correct rails Do this with the bridge "Open" so you will have enough wire to open the bridge

If you want to add a safety switch (pressure switch) you will have to insulate both ends of the "power side" of the lead tracks about 2 feet on either side of the bridge.

The circuit is simple. Follow the diagram below. The green is the power feed wire, either DCC or DC throttle. This wire attaches to the Common terminal of the pressure switch. The red wire goes from the Normally Open terminal of the pressure switch to the rails as shown by the red wires. this effectively makes the 2 foot leads & the bridge a separate block.

Well - that's it - hope you had fun reading this - now go build one!!! If you have any questions - PM or e-mail me & post pics of your progress

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