how to put hinges on atlas bridge over my walkthru ?-track moves 1/4 inch when lifted

You would do well to contact forum member Susan Deats:

http://www.slsprr.net/features/bridges1.htm

The solution in the link may be more elaborate than your requirements, but I'm sure she can supply a simpler, but effective, solution.

The hinges have to be higher than the rail head; this will keep the rails from jamming together when you raise the bridge. 

John

It can be done with the pivot below track level, but you need to move the pivot away from the edge of the bridge. It also helps to cut the track break at an angle so that the moving piece clears the stationary one. Dont use the bridge as the track break, put a few inches of track on the end of the bridge so you can mess around with getting the joint in the right spot. You might end up with a small gap in the rails for it to open/close, but as long as its not too big, you wont have any issues. Just make sure that the open end of the bridge has appropriate alignment measures to get the bridge down in the same spot every time. 

I would also level the bridge so you dont add a 3rd dimension into the equation.

Yes you can do this but it takes some work. I made a single track bridge into a hinged unit but it takes some drill time some all thread rod spacer nuts and a hinge mechanism.  Works great.

Yes you can do this but it takes some work. I made a single track bridge into a hinged unit but it takes some drill time some all thread rod spacer nuts and a hinge mechanism.  Works great. Ill try to post some pics tomorrow note on the hinge 

Bucca - hinged lift bridges have been a subject for several previous discussions on OGR -- if you search the site for "lift bridge" or "hinged lift bridge" you will see a long list of previous threads.  Here's one of the more recent ones that has some nice pictures:

https://ogrforum.com/...c/hinged-lift-bridge

the key for easy success is indeed to have the hinge pins just slightly above the top of the rails - you can get fancier in terms of trying to hide the hinges and have the hinge point below the rails, but then you've gotta mess with cutting the track at an angle to accommodate the pivot arc, which can be a real PITA.  About half way down the above link you will see what I think is really the simplest solution - two wooden blocks on either side of the track (total of four blocks) attached to the table and to the bridge (or whatever it sits on) and two small hinges opened flat spanning the blocks (the blocks raise the hinges up so they are just above the rail top).  I've seen other pictures where folks have painted the hinges and blocks and detail them with scenery materials to hide them (or make them look like part of the bridge).

At the other end, you need to have something to keep the rails aligned horizontally - again the simple solution is a couple of pins and sockets that the bridge assembly will engage when its down.  One other feature worth considering is having a microswitch or some other electrical contact on both ends of the bridge wired to the track section/block on either side of the bridge so when the bridge is in the up position, there is a dead block to keep the trains from inadvertently speeding off into the chasm (or raised bridge) -- its been known to happen.

In the above link you will also see Susan Deats link to her work - which is really quite well engineered, including a gas piston device (like on the tailgate of an SUV) - so if you are really handy with tools and metal working, its a more elegant solution (but it still has the hinge point above the rail top).

- Rich

ps  If you look at some of the woodworking stores (like Rockler or Lee Valley) - or a local hardware store, you can find fancier hinges -- I think there is something called a scissor hinge, which is the equivalent of what Susan built. 

Bucca - a quick addendum to my note above - my suggested solution is more than half-way down - in fact most of the way to the end.  Look for a post from BXCXDAN, who shows his work with an Atlas bridge.  In addition to the hinges, he also has a nice set of stops for the bridge to rest on when in the up position.