If I place my main line on cork bed and have my loco pass on to a bridge - what is the best way to adjust for the difference in heigth between the main line and the bridge overpass? Do I place cork under the bridge supports?
You would adjust the bridge height ( bridge shoes on the abutment) to have the track continue on to the bridge. It is not nec to use any roadbed on the bridge. Usually on any open decked bridge the rails are run on top of bridge ties. This is done on wood trestles, steel viaducts, plate girder and other open decks. If you use a ballasted deck you could just carry the flex track across the bridge with or w/o any roadbed. Micro Engineering does have a bridge flex track available in both "N" and HO. This track incorporates a thicker bridge tie to look more prototypical.
This is the ME bridge flex track running across a steel viaduct
The bridge girder deck of this CV bridge is positioned to rail height by the "sub" abutments or the center pier height. The abutments are to be covered w/ plaster castings
This ballasted deck stone bridge actually has the wood spline, roadbed and track running across the cut for the stone arch
Modeling B&O- Chessie Bob K. www.ssmrc.org
While this layout used homasote for the roadbed, the same principal would apply to cork. Adjust the abutment and bridge height to continue the rail height across the bridge.
Here's a good view of a transition to a bridge. The sub structure is a lot like the one posted above, The embankment ends at a concrete bridge abutment, which supports the bridge structure. There is cork roadbed under the ballast that leads in from the right, and the top surface is flush with the top edge of the abutment. (actually the abutment is placed in the scenery so it ends up flush at the top). I built the abutment from styrene so I could make it fit specifically with my scene and my prototype. Note that there are three sides to it, which work to hold the roadbed material in place.
Once on the bridge, the track changes from regular main line track to "bridge track". The ties are square, longer, and spaced a little closer together. There's also added plate detail to allow you to add the guardrails between the main rails. Micro Engineering makes bridge track in HO and N scales, and in several rail heights.
As with just about any other question about model railroading, if you study what the prototype does, the answers to how it should be modeled become pretty obvious. Do a google image search for "railroad bridge abutments" and you'll find a treasure trove of images and information in a matter of seconds.
Hope this is useful.
Lee
Route of the Alpha Jets www.wmrywesternlines.net
As you can see, the solution is typically to buld the bridge with all the parts, including the shoes, place them on your preferred pylons and abutments, and set them all in place as best you can with bits of wood and stuff to stabilize them. Then get down to rail height level and take a close look for height discrepancies. If you see one, either because the entire structure and supports are not high enough and so both ends and the deck are too low, or just one end is low, shim some more with door frame wedges cut to suitable lengths and try to get it right. When you sense that you are as close as you will get it, you can eyeball what you have done down on the creek bed, or whatever you have at this stage for your supporting surface(s), and carefully remove those stacked items, leaving the shims and other materials used to alter the elevation(s).
Here is where you decide what to do. You can build platforms out of wood that may be covered with tinted 'water and creek bed materials, or you can build up ground goop if it is a ravine...you want to anchor the bridge and pylons well, but not reveal the supports at all. Will that be with more 'concrete' or stone layers if your pylons and abutments can be grown with pieces, or must you recast larger ones yourself using your own molds as many of us do? Figure it out and make sure that, before you begin to scenic around the pylons or abutments that the bridge sits securely in place, and that all four rail ends are a good match for alignment in all planes with the oncoming rail ends.
In fact, just to be absolutely sure, I lay a full 3' section of flex across my bridge decks so that any joins are at least 5-8" into the terrain. Then I know how much to lift the deck to where it supports the length of flex at grade. It is at this stage that I actually begin to shim up the supports for the bridge and learn how much more I must add to make it a real bridge. Once the bridge is in place and anchored, then I finish the scenery around and under it.
-Crandell
Hi,
Its from from Malcom Furlow I get this idea and have use it severals time whith good results.
I think it was in the San Juan series, he cut away the roadbed so the flextrack stand alone in the air.
After that he glue the bridge to the track by coming under it..
The foots and abutments where adjusted to the now supended bridge.
This work well for small open deck bridges.
For longer bridge I use a small tube of aluminium which stand on the two ends where the track is still on roadbed.
I put a few elastics to keep the track against the aluminium tube and put the bridge under the track by gluing it. When dry and the foots in place I cut the elastics.
Marc