The end

This is where I ended up, with a functional bridge.

It is constructed of aluminum extriusions, and spans about 44 inches across the doorway.  There is about ½" of clearance between the closest point of door swing and the bridge, so if someone opens the door wide, even suddenly, it is not a problem.

The main structural member on each level is a 44 inch piece of channel, like the sample above.  It is "wall-track", used for office partition walls, and is the piece normally fastened to the ceiling, with the wall panels in the groove on each side.  I was able to acquire a couple of scrap pieces for the asking (although, with scrap prices going up, it would probably cost me a few dollars, now).  The channel was used, face down, with aluminum angle (more wall partition trim pieces) as fences, or guard rails.  I pre-drilled holes, then used self-treading stainless steel screws to fasten the angle to the main member.  This was done for each level of the bridge.

Next:  where the hinge points belong.

Hinges

My first take on hinge selection was to just use some door hinges, but as I thought about it, it became quickly evident that I had a problem, if the track or any portion of the bridge, was above the pivot point.

Suppose the side view of the rail is the hatched portion of the drawing, then you can see where the interference happens as soon as the bridge is raised.  The solution was to move the pivot point up, like this.

That sent me off to the hardware store, in search of something I could use.

These cabinet door hinges were just the thing, and they were out of the way the the track.

Watching very carefully....

I've got a problem bridge myself... I'm going to be watching this thread very carefully for ideas - I already like the hinge one.

A different place for the hinge

I also have lift bridges across the entrance door and across an operating area. I needed bridges that could be opened quickly and often. I was also concerned about an unattentive operator running a train off an open bridge.

I placed the hinge such that the hinge end would drop down as the other end was raised. This avoided interference with the track at the joint and also provided a barrier for a train about to go off the deep end.  Note that power is routed to the bridge from this end. The bridge is allowed to swing a little over-center vertically so it is self-supporting when raised. It is kept raised except when operating so there is very little tendency for it to sag.  

The other end is located by shelf pins mating with a steel mending plate on the bridge. The mending plate holes are just a smidge smaller than the shelf pins so I gently reamed them out until it was a snug fit for alignment. The mending plate and shelf pins also route power to the tracks on the right of the bridge so that section is unpowered when the bridge is up, keeping trains from running off that end. 

I also installed guard rails at each joint to help guide the wheels across the small gap.

hinges

That's another good way to do it, George.  For any who are looking at solutions to where to put the pivot, either draw up a plan or sketch, or make a cardboard mock-up, then play with it a bit.  Any problem should show itself quickly.

I like your idea of a fail safe electrical feeder using the pins.  The bridge lead only has power when the bridge is completely in position.  My solution cost more:  I'm hard-wired with stranded wire, with a microswitch to complete the connection.  And I'm not satisfied with its location.  I just may "borrow" your idea; it certainly fits my budget!

For any looking at this, you'll notice that George did not use "loose pin" hinges, so there is no play in the installation.  That was something I looked at when I selected the cabinet hinges.  The pivot pins are a good fit, with no slop (being cabinet hardware), so the end of the bridge does not move. 

I doubt that the hinges I used would be the correct choice for the more substantial mass of George's plywood-based bridge.  The aluminum extrusion version is very light, so the small hinges I used are OK, though they would not withstand lateral movement such as an accidental collision or someone leaning heavily on the bridge.

End alignment

The next step was to figure out how to support and align the other (non-hinge) end of the bridge.  It had to land in the exact location and remain there, every time.

I cut the extrusion so that it overlapped the subroadbed plywood by about ½".  Then I drilled two #29 holes (0.136" diameter) through the aluminum, then a little way into the plywood.  Then I inserted 8d common nails (0.135" monimal) into the holes and drove them to a secure fit in the plywood. I cut of the heads of the nails and filed them smooth.  Voila!  alignment pins with a good fit.

The photo also shows how I can adjust the track alignment.  The end of track is fastened to a piece of basswood that has slots drilled/cut on each side.  I can loosen the screws, adjust, insert shims underneath for vertical adjustment, as necessary for perfect alignment.  The adjustment screws thread into Tee-nuts imbedded into the underside of the plywood subroadbed. 

I'm using code 100 track on the bridge and approaches, because of its rigidity.  The main section is a piece of Atlas flex track, with pieces of Atlas straight snap track soldered to each end to maintain it absolutely straight.  It is laid on a piece of basswood the same thickness as the cork roadbed I use.  The track is glued to the basswood, which is in turn glued to the aluminum.  I used the same latex adhesive caulk that I use for applying cork roadbed and for track laying.

For insurance, I added a machine screw at each end of the bridge trackwork.  I drilled #50 through the tie, then drilled #43 through the aluminum.  Then I tapped the hole in the metal 2-56, and used a stainless steel 2-56 screw and washer.  (The tap and drills came from my Kadee coupler install kit).  You can see the screw and washer in the photo.

I was going to use guard rails, but so far it has not been necessary.  The biggest test so far was backing a train, with the cab-forward shoving, through the curve and across the bridge.  Success.

The lower level

Once I installed and tested the top level of the bridge, I started making an identical one for the lower level.  This time, I had to cut the span a bit shorter, because as the two levels rotate up as a unit from that pivot point above the upper level track, so the lower level is offset.  With six inches of height difference between levels, the lower end had to be about ½" shorter to clear the upper level fixed edge.  I had to add an extension to the lower fixed (plywood) end to compensate (I had built the fixed subroadbed a few months before, and hadn't thought it though.)

The lower level is hung from the upper level by lengths of 3/8" diameter all-thread, with double nuts top and bottom.  This allows very precise height adjustment, and once the nuts are tightened, it all became very rigid.  The lower track on the hinge end of the bridge aligns without any extra alignment pins or guard rails.  I was really surprised at how rigid it was:  it does not move laterally at all.  I had picked the 3/8" size only because I had it in the garage already.  There is almost no weight to the bridge components themselves,  so the 3/8" was over-kill for support, I thought.    The black cover over the all-thread is a piece of polyethylene sprinkler system tubing (in the drip irrigation aisle of the HW store). 

I should explain the nut-tightening.  On each bridge level where the all-thread penetrates the aluminum, there is a nut on the top of the aluminum, and a nut immediately under that same piece of aluminum.  Tightening is by holding the bottom nut with one wrench while tightening the top nut with another wrench.  (It's called a "jam-nut" ) .  You're basically turning the wrenches opposite directions until the nuts jam together or sandwich whatever' is in between tightly. 

Once you've tightened the top studs, there are four rigid points to attach the lower bridge to, and do height adjustment by means of the lower nuts.  A quarter turn of the nut moves the bridge up or down about 1/64", so you can be very precise.

I did add a small alignment block to constrain lateral movement on the lower bridge end.  A better solution would have been to remove and replace the lower plywood subroadbed with a longer piece, so I could have used the same type of alignment pins as I did above on the first level.  (Maybe next time!).

Hi Some years ago we

Hi

Some years ago we scrapped our old club layout and started again. Amongst other requirements was a geriatric bridge. This needed to carry four tracks of mainline and one branch across the entrance into the hollow centre of the layout. In addition the branch line was about four inches above the mainlines.

The whole board was about 1'6" wide constructed of 1" ply with hinges on 6" pillars to raise the pivot point above the track level of the branch line. The structure was quite heavy so we counterbalanced it with a rope running over a pulley. Initially the counterbalance was a large can of paint that happened to be handy but this has been replaced to allow its use and to compensate for the additional weight of scenery. The rope runs from the end of the bridge up to a pulley over the hinges, then to a second pulley against the wall. The angle of the rope means that the counterbalance is insufficient in the down position and more than sufficient in the up giving stability in both positions. In fact the counterbalance was adjusted to give neutral compensation with the bridge halfway. The counterbalance runs in a length of drainpipe to avoid interference.

The mainline is curved at 4ft radius across the bridge. This results in them being approximately normal at the free end but at 45deg at the hinge end. We cut the deck in a zigzag in order that all tracks would be normal to the joint. However if building it again I'd use check rails and leave the track at 45deg. One check rail would be on the abutment and the other on the bridge. However the bridge is well located in the down position with pattern makers dowels which ensure that it is always spot on. We also never leave the bridge in the up position both to avoid the risk of a slam and to avoid the risk of twists developing.

There are catches to lock the bridge down and microswitches to sense location. These microswitches disconnect  all running tracks within about 8ft of the bridge. At one stage we intended using interlocking mechanical frames, signals and turnout operation and the two frames adjacent to the bridge were built with a release lever for the bridge. Unfortunately, to my mind, the club members have changed their minds and all turnouts are now electrically operated, there're no signals but turnout position is displayed on large panels.

Archie

Lift bridge

Great thinking...I spent days building a wood trestle that's hinged, but- the door frame idea is so cool and simple yet durable...excellent job.

Lift Bridge

I have been wrestling for weeks as to how to design and make a lift bridge.  I appreciate very much the help that the lift bridge blog and the comments on it have been.  This demonstrates the value of an online forum such as this.

Help with my Lift Bridge

Hello Everyone,

I am new to this site. I have a three foot wide lift bridge that I am trying to get to work properly.

What is happening is the track binds after the bridge is in the up position. No matter how I try and adjust the track it is either to far apart, leaving a massive gap or so close that the tracks bind.

Should I do the door frame method as mention in this thread? Then again, how do I avoid the tracks from binding?

How does one post pictures here?

Roy

Lift Bridge at Sudbury Division

Well this was put in before I was a member in 2009, but it's worked great ever since.  This is from our websites construction gallery.

http://www.wrmrc.ca/construction47.html

I thought there was more information on it's construction, but I couldn't find it.  Perhaps the guys can chime in if they see this.

A push button releases the magnet that holds it in place and allows the bridge to be lifted.  There is also a power cut off on the blocks approaching the bridge from both directions to prevent any unattended mishaps.

The bridge is double track and on a curve.

Thanks

Sean

Jurgen it's in the JL&T Lift Out Bridge thread...

Jurgen,

You did place the Sudbury Swing Up Bridge construction details in our JL&T Lift Out Bridge thread.

Jas...

You were probably addressing Sean, Jas

But nevertheless, I did post that drawing on your thread.  Sean was probably thinking of a photo gallery on our facebook page:

http://www.facebook.com/media/set/?set=a.240184426035854.64686.133062913414673&type=1

It shows some of the construction details of the bridge we built.  The key to avoid binding is to angle the joints so that the fixed and moving parts can separate and come together without rubbing against each other.

I knew I seen it somewhere

Thanks Jurgen, I knew I read up on it somewhere

Sorry for the repost guys, hope that helps though.

Thanks

Sean

picture posting

Roy,

Try this thread for a "how-to" on posting photos.

http://model-railroad-hobbyist.com/node/621

Once you post a sketch or a photo, we'll be able to get a better idea of the particular problem, then someone on this forum should be able to help.  We've got a lot of bridge builders and "McGyvers" around this site.

Update

March 14, 2016

I received an inquiry today on a model rail Yahoo group about use of aluminum for lift out or swinging bridges, and since mine has been in flawless operation for 5 years, I'm just bumping this blog posting forward.

(Note to MRH:  I found no way to merely send a URL pointing to node/5551 on the forum; it requires a logged-in MRH subscriber.  So, this is my solution)

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