Is it okay to install all my subroadbed (either ribbon or cookie cutter) and then purchase my bridges under the assumption that I can simply cut the plywood subroadbed at the points where my bridges will go at a later date. Or is the canonical method to have the bridges on site when installing the subroadbed so that they get installed while installing the subroadbed?
I can’t think of any reason not to simply run all my plywood subroadbed, and then go back and cut out sections where bridges will be AFTER purchasing the bridges, but no one seems to advocate this in any books that I’ve read. In fact, I’m thinking that I can actually run all the (cork) roadbed and track, as well, to make sure all my grades are okay before installing any bridges, at which point I’d then go back and cut the track, roadbed and subroadbed all at the same time to install the bridges … but, I’m wondering if I’m missing something. Thanks!
Your method seems very logical to me as well. I think with many aspects of this hobby there are many ways to get to the same end point. There is no definitively right and wrong way to accomplish something.
I think your idea of cutting out the sub roadbed is the best idea. Plan your cuts and make sure that you put supports under where the ends will be before you cut them out.
When I built my railroad, I made the mistake of cutting them 1st. I then had a tough time making sure the grade matched. I found this out when laying track. I thought I planned it right, but I had made a mistake somewhere. Next time, I’ll know better.
That’s the way I did all my bridges. It’s nice to see the grade work bfore cutting in the bridge, but plan ahead and make sure there will support for the roadbed on either end of the bridge after the bridge is cut in.
The only problem with this method occurs when you are passing over another track at minimum clearance. I didn’t have the clearance to extend the subroadbed and roadbed in place of the bridge due to vertical clearance issues. I hate it when that happens!
Also, as others noted, make sure you have the subroadbed locked in place with supports at either end before cutting. Don’t ask me how I learned this one, too!
yours in learning from my own mistakes instead of others’
I personally like to have the bridge right there while I’m working on the terrain and track work approaching it, and under it as well. To me, it’s a lot easier to visualize the finished product if the bridge is really the one I plan to put there. It also helps to know the exact size of the bridge when working on the scenery.
I had all my track running on basic ply-strips and foam road bed. I then added bridges. Some added easily. For some I had to adjust track and even replace some when the bridge didn’t fit. If you are prepared for some adustment, you can have your trains running a year or two earlier if you are planning many large bridges…
I did this for my latest layout. I manufactured all the spline roadbed to be an essentially monolithic structure when it was closed up. I knew, though, where I wanted my trestle. When it came time to insert the trestle, I had already built the gorge. I had previously cut the section of spline roadbed with a hacksaw…or was it a drywall saw…don’t remember, and then shaped the aluminum window screening and added plaster goop so that it would look like a proper gorge. I shaped the lip of the gorge when I installed the trestle so that the wooden and dirt-filled abuttments on either side could be manufactured in place to look realistic.
Then, having made each trestle bent a long approximation of the vertical distance it would have to extend, I merely nipped them with cutters until they fit snuggly. They had to fit against a sill plate, and snug up against the tracks that I had inserted over the span, without deviating from the grade.
Yes, I always build all the roadbed and lay the track first … that way you can be sure things are working well. Most bridges need straight track, although you can build a bridge on a curve with some planning. When doing your roadbed, make sure the roadbed is straight for the length of your bridge while you are building the roadbed.
Before removing any of the track and roadbed at the bridge site, make sure the ends of the roadbed that remain at the bridge site are well supported with a riser close to the bridge at each end. This will keep the roadbed from shifting around when you remove the section of roadbed where the bridge will go.
If the bridge will be on a curve, I take a pencil rubbing of the railheads before I remove the track and roadbed at the bridge location. This way the new bridge rails will match the old track exactly.
By taking these steps you will get a great bridge with smooth and completely aligned trackwork on the approaches.
I lay the subroadbed out as a solid structure. Most of the time, I have the actual bridge in hand, so I can tailor the subroadbed to match the bridge structure. For nearly all of my bridges, the subroadbed runs uninterrupted through the bridge.
That’s very useful to know … especially since 3 of 4 of my planned bridges are going to be on curves, thanks!
Unfortunately, I have hit one small problem with not having any of the bridges yet; I have a straight section of double track (HO scale, which will probably just be a Truss), but I’m not sure what width the two tracks need to be (e.g., 2", 2 1/4", etc.). I suppose I’ll simply have to track down the manufacturer’s dimensions, which means I’ll need to know which one I’m intending to purchase … argh!
Wanting to install a single section plate deck bridge I did a search and found this thread. Helpful in that it spurred me to go ahead and start my installation. Since I have a new install I decided to build the frame and subroadbed before installing cork and track. Worked out very well. I have an opening in the subroadbed which I have tempo. filled with a removable section of subroadbed and cork on top. Now I can intall track and when ready to install the bridge all I have to do is remove the temp. subroadbed and cork . I will build the track with a removable section to allow the bridge to be intalled and then relay the track.
Put me in the camp of those who prefer to build the subgrade first. In places where I know a bridge will be added, I actually install two separate subgrades, one at roadbed level and one about 1/4 inch below the bottom of the drainage to be crossed. That way I can easily provide for abutments and pier foundations, secure in the knowledge that everything will remain solidly in place when the upper subgrade is cut out.
Also, most of my bridges are deck girder type. For them, I don’t even cut the subgrade. I just narrow it so that the girders are the correct distance apart when I apply them to the sides of the plywood. Between view blocks and the closely-spaced bridge ties, it would take keen eyes to notice that there’s no daylight between the girders.
Chuck (modeling Central Japan in September, 1964 - with LOTS of bridges)
Hi, if I can wade in with some spex for you, the Walthers Cornerstone 2-track thru truss bridge I assembled and will install soon has the following dimensions: The box says it is 15" long, but my assembled unit is a bit shy of 14 7/8" (allowing a 1/16" expansion/contraction space at each end will swallow the extra OK); track spacing is 2 1/8" on this one.
I built all of my roadbed as a 1-piece laminate of 2 pieces of 1/4" ply glued together to make the equivalent of a 1/2" subroadbed. (Think of an 11’ x 14’ cookie-cutter folded dogbone that crosses over itself.) Then I cut the opening for the bridge and temporarily am running trains across a plywood ‘bridge’ until I finish building what’s going to be below. Remember to allow for approach alignment and for your bridge guardrails when plotting them.
I’ve done it both ways. Both work as long as you are careful with measuring and cutting. The advantage of your way is that you can get things up and running and still have time to change your mind on a bridge location without having to repair subroadbed if you decide to move one.
