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Elevation and Track Alignment

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  • Member since
    February, 2018
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Elevation and Track Alignment
Posted by BHandK on Thursday, February 08, 2018 9:49 AM

I'm back to building the Granite Gorge & Northern after a 5 year hiatus.  I'm also bedeviled by a problem I had the last time I was working on it.  That is that I'm unclear what to do about making the track from the top of a subroadbed incline (cookie cutter plywood) line up evenly with a level bridge.  I have a picture here is anybody has any suggestions on what I need to do to make this work.  TIA

track elevation alignment problem

 

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Posted by jjdamnit on Thursday, February 08, 2018 5:46 PM

Hello all,

As you are using cork roadbed I would suggest sanding the roadbed to provide a smooth transition.

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

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Posted by SpaceMouse on Thursday, February 08, 2018 6:03 PM

BHandK
That is that I'm unclear what to do about making the track from the top of a subroadbed incline (cookie cutter plywood) line up evenly with a level bridge.

Actually I see two things causing your problem. 

The first is that the right side too high for your bridge. That part is probably obvious to you. 

The second thing is that you are going straight to the bridge at an angle. You need to provide a vertical transition or an easement. That is, you gradually change the slope of your track back to level.

What I do with bridges is to take the cookie cutter all the way across the bridge area and make sure it works. Then you can cut the plywood out and add your bridge. IF you do it this way, the bending of the plywood will naturally provide the easement. 

What I think you will find is that you need to start your grade farther away from the bridge.  

Chip

Building the Rock Ridge Railroad with the slowest construction crew west of the Pecos.

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Posted by BigDaddy on Thursday, February 08, 2018 6:32 PM

There are probably some optics going on, but it looks like the track, besides not having a flat transition, is going to be 3/4" too high by the time it reaches the bridge. 

Whatever grade it is; it needs to be reduced at least over your longest car length, before the bridge.  Otherwise you will be asking why your cars uncouple at the kink.

 

Henry

COB Potomac & Northern

By the Chesapeake Bay

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Posted by floridaflyer on Thursday, February 08, 2018 8:00 PM

You have to reduce the grade gradually leading up to the bridge and have the track level leading into the bridge. As Chip stated that means starting you reduction of grade well before the bridge. If is is a 2% grade then reducing the grade by say .5% per foot would mean that you would have to start at least 4 feet from the bridge. It may be possible to reduce it a bit more and shorten the start point but in any case the grade has to be reduced gently leading to the bridge. It is the same process as the gentle increase in grade that is necessary at the start of the grade.

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  • From: Bradford, Ontario
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Posted by hon30critter on Thursday, February 08, 2018 11:49 PM

Hi BHandK!

Welcome to the forums and welcome back to the hobby!!  Welcome

You have to lower the grade leading towards the bridge, and you have to build in a transistion from the sloped track to the level bridge. The transition will need to be four or five times the length of your longest cars (there is a formula for calculating vertical easements but I can't find it. Maybe another forum member can post it). You might have to rip the entire length of graded track out and start from scratch.

Dave

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Posted by selector on Friday, February 09, 2018 11:09 AM

Your picture doesn't show up for me...only a black and white square with an X.

If you are using plywood as sub-roadbed, you must make a riser a few inches back from the bridge deck and have the sub-roadbed sit atop the riser.  Then, you have another riser just before the bridge deck, and its top surface, to which you will screw the plywood sub-roadbed, will be 'at grade' so that the bridge deck, minus track, is fully level with the sub-roadbed...minus track.  The idea is to get the tracks to crest a bit before the juncture between sub-roadbed and bridge so that the tracks don't hit uneven surfaces there, and the trains will smoothly ride over the abutment and over the bridge.  

What you should picture is the sub-roadbed curving over the first riser a few inches back, probably close to 10 inches back from the abutment.  The curve is imparted by the rising angle of the sub-roadbed having to adapt over the unyielding first riser and being forced back to the grade of the bridge.  BTW, bridges don't have to be level, but they should not have changes of grade over them.  It's just that, on our constrained layout spaces, a bridge/overpass is often practically at the apex of our level changes because soon we have to descend to get back down to close our loops...if we have loops.

To get a smooth onset into the grade at the bottom of the rise, you do the same thing, essentially.  You anchor the plwyood sub-roadbed securely while it's level, and then force a curve into it by placing a riser 9-12 inches further in the direction the tracks are to go, the sub-roadbed complying.  The riser's top must force the rising curve you want, called a transition, into the plywood.  A second riser a few inches further establishes the consistent (ideally) grade you need to get up to the higher reversing transition I was describing at the begining.

 

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Posted by BigDaddy on Friday, February 09, 2018 11:40 AM

selector
Your picture doesn't show up for me...only a black and white square with an X.

Here is his pic

 

Henry

COB Potomac & Northern

By the Chesapeake Bay

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Posted by selector on Friday, February 09, 2018 4:22 PM

Thanks, Henry.  Yup, the oncoming tracks appear to be quite a bit too high. He must plane or sand for several inches if he needs to keep the general construction, but he also needs to extend the sub-roadbed.  To to that he needs a cleat glued or screwed to the side of the pier we see at right and he needs a second riser immediately to the right of the bridge pier.

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