This topic concerns the modelling of the railbed for my Cheverie Mountain Railroad layout. The prototype can be broken down into 4 parts: subgrade, sub-ballast, ballast, and interceptor ditch. The rails and ties are not part of this discussion.
Section 1: Subgrade
My demonstrator workstation is shown in this photo. It is a custom-made plywood platform with an area to rest tools (red), border wood (black) to contain everything, and two pieces of 3/4" EPS foam (white) stacked one on top of the other. The top one you can see is the subgrade.
I have placed an HO-scale Walthers GP9M Rail Link Locomotive on the subgrade so you have a better feel for the size of the work area.
The top surface of the subgrade is not horizontal on the ground. CN specifies that this surface must slope down from the center of the railbed by at least 40:1 (I am assuming for drainage). Because this is a mathematical inequality, the company's engineers must choose a slope then calculate how wide it needs to be. These calculations (simple algebra) require the CN specifications for the sub-ballast dimensions sitting on top of the subgrade as shown in my 1/2 cross-section.
The sub-ballast must be 24' wide and 12" deep. Since I only need a 1/2 cross-section drawing because of symmetry, the sub-ballast extends 12' from it's center. This, and the specified outside slope of the sub-ballast (2:1), are all I need to calculate the width of the top surface of the subgrade (foam) and the depth at the outer edges. Then I can modify the foam for the railbed before dealing with the sub-ballast.
I cannot recall the size of your intended layout or the number of linear feet of mainline track, but are you intending to apply these dimensions and maintain these slopes across the entire track portions of the layout? If so, this could be quite an undertaking.
Rich
Alton Junction
richhotrain...are you intending to apply these dimensions and maintain these slopes across the entire track portions of the layout? If so, this could be quite an undertaking.
I agree with Rich. Also, do the calculations take into account superelevation on curves or is that accomplished in a different part of the overall roadbed profile?
Wayne
One step at a time. First I complete the demonstrator with straight only to see what is involved. I just got back from one industrial line (Hantsport gypsum) and one CN line (Windsor Junction) and have hundreds of close-up track photos along straights, curves, and turnouts. I also took plenty of measurements. Both lines are in my real layout area.
I do wonder at the need and wisdom of modeling a drainage slope, evidence of which cannot be detected in the final product.
On the other hand, modeling the visual effect of the various "subs" is rarely done. People think that ballast "just sits on the ground". Drainage, in particular is rarely modeled.
I do hope that the track, once installed, is properly superelevated, as noted above. And also, that the curve radii are prototypical. THAT is very visually evident.
Ed
7j43k I do wonder at the need and wisdom of modeling a drainage slope, evidence of which cannot be detected in the final product. Ed
I will know the slope is there and that's all that really matters. I will be able to say that my railbed meets CN Industrial track standards. This is not what CN does on their own lines as I can plainly see in today's photographs, but this is what their industrial customers must do. As for the Hantsport industrial lines I saw today, you cannot tell that there is a drainage slope either so I will be right on prototype.
As for the wisdom part, I will know how to do it for a model or for the real thing!
I see that CN requires a maximum curvature of 9 degrees on industrial trackage. That would be 88" for an HO model. I look forward to how you handle that.
OldSchoolScratchbuilder One step at a time. First I complete the demonstrator with straight only to see what is involved. I just got back from one industrial line (Hantsport gypsum) and one CN line (Windsor Junction) and have hundreds of close-up track photos along straights, curves, and turnouts. I also took plenty of measurements. Both lines are in my real layout area.
Calculations complete. In HO scale the top of the subgrade is 9.9 cm wide and drops at the outside edges by 1.2 mm relative to the center. This is completely do-able so I will experiment on a foam pressing technique this evening. This calculation makes me happy and that's important to me.
richhotrain Still curious, though, how long will your mainline be?
Still curious, though, how long will your mainline be?
One additional note on the HO 1.2 mm depth. This only happens if the company engineer uses the CN minimum slope of 40:1. Any other slope choice reduces the 1.2 mm depth.
7j43k I see that CN requires a maximum curvature of 9 degrees on industrial trackage. That would be 88" for an HO model. I look forward to how you handle that. Ed
Let me give you an example. On part of my layout, I model Dearborn Station in downtown Chicago. From Polk Street on the north to Roosevelt Road on the south is 4 city blocks, or 1/2 mile, or 2,640 feet. That is 30.3 feet in HO scale. From State Street on the east to Clark Street on the west is 3 blocks or 1980 feet which is 22.75 feet in HO scale. But, I only had a 12 foot x 8 foot area to work with.
So, you are going to need to take that consideration into account.
7j43k I see that CN requires a maximum curvature of 9 degrees on industrial trackage. That would be 88" for an HO model. I look forward to how you handle that.
This thread is about the CN railbed cross section detail (one engineering drawing). Has nothing to do with main lines, curves, rails, crossties, level crossings, rail yards, hills, bridges, bumpers, switches, compression schemes or anything else. One CN drawing at a time so if you have a question on that drawing, look it up if you haven't already, I'll have an immediate answer that is appropriate to this thread. I will be finished this thread in a few days.
This is more real to ME than buying a piece of cork from the hobby shop and gluing it on my foam.
If you see a mistake in my calculations I'd like to know that.
Here is an alternative to understanding real track beds. https://m.youtube.com/watch?v=78sWxnY07c8
OldSchoolScratchbuilder 7j43k I see that CN requires a maximum curvature of 9 degrees on industrial trackage. That would be 88" for an HO model. I look forward to how you handle that. This thread is about the CN railbed cross section detail (one engineering drawing). Has nothing to do with main lines, curves...
This thread is about the CN railbed cross section detail (one engineering drawing). Has nothing to do with main lines, curves...
Yes, you state the obvious.
And I do still look forward to how you handle 4.2 of the CN specifications.
7j43k Yes, you state the obvious. And I do still look forward to how you handle 4.2 of the CN specifications.
You'll be waiting until late summer at the earliest. I am working on Section 3 for this small but complex demonstrator. There are no curves. After the earthwork, I add straight track and ties, wire the demonstrator, build the automated hopper loader, add ground cover, elevation contours, buildings, pavement, and lots more before I get back to my layout. The demonstrator is not covered here only the straight track bed.
I have given up on posting anything about my layout because of all the criticisms so you'll only be seeing small bits of my work at a time. That initial layout work is in the layout forum if you were not aware and I have stopped posting there.
OldSchoolScratchbuilder I have given up on posting anything about my layout because of all the criticisms...
I have given up on posting anything about my layout because of all the criticisms...
You have an interesting and unusual approach to model railroading. I have seen not so much criticism as questioning. Either way, you have put yourself very much out in front of us. You should not be surprised by either criticism or questioning. If either of these threaten you, you may withdraw.
7j43k OldSchoolScratchbuilder I have given up on posting anything about my layout because of all the criticisms... You have an interesting and unusual approach to model railroading. I have seen not so much criticism as questioning. Either way, you have put yourself very much out in front of us. You should not be surprised by either criticism or questioning. If either of these threaten you, you may withdraw. Ed
Ed, your questions here are not criticisms just off topic. My layout posts in the layout forum was another matter. I am building an 18" demo here and there is no layout. So the answer to your question about 4.2 is that I do not have a curve on my 18" demo.
In the middle of the night I woke up with an easy solution for making the gentle slopes of the subgrade. One of my wife's heavy antique irons. Pulled out a spare piece of foam and the weight of that heavy iron made it easy to push into the foam. Will use it on the 18" demo track today.
On a scrap piece of foam I can easily press the subgrade slope with an antique iron. The initial problem I had was friction between the iron and the foam - foam squeeks woke my husky up. A little dirt (processed sandstone from Cape Blomidon) and problem solved. I'll use this technique on my demonstrator.
Subgrade on the demo is complete. Used approximately 9.9 cm width and 1.2 mm depth at the outer edges. Applied processed sandstone particles from Cape Blomidon, pressed the slope with the heavy antique iron, checked the slopes with a level periodically, and finally a gentle spray of Scenic Cement. Will let this subgrade dry over night. Tomorrow I will start the sub-ballast section.
A very good article on curved track and prototype curves was written by Bob Cushman, "Curved Trackwork," Model Railroader, Vol. 23(10), October 1956, pp. 54-57.
Section 2: Sub-ballast
Thin layer of sandstone dried very quickly so I was able to start the sub-ballast. Six aluminum L-blocks (stained glass window supports) were pinned down with their vertical outside faces separated by the CN 8.4 cm spec. The 2:1 slopes (30-degree up angle) were filled and shaped up to a 3.5 mm height on the blocks with my processed Grade 3 shale particles from Walton, Nova Scotia. Finally, the outside shale slopes were sprayed with Scenic Cement. Tomorrow I'll be able to fill in the remainder of the sub-ballast. I am liking the railbed so far.
Sub-ballast is now finished. I removed the L-blocks and the shoulders remained in place as I had hoped. Filled the inside with more Grade 3 shale sub-ballast (I make my own at no cost) and shaped the gentle 40:1 slope with a small block of wood. Another Scenic Cement spray down and let it dry. I may be able to start the ballast section later today.
Section 3: Ballast
Six aluminum blocks are pinned on the top of the sub-ballast leaving the standard tie length between their outside vertical surfaces. A finer Grade 2 shale ballast is applied to the outside surfaces of the blocks following the slopes and dimensions in the CN drawing. Another spray of Scenic Cement and tomorrow I'll finish up the inside ballast.
I don't get all the pinned down aluminum blocks. What's up with that? Why does the sub-ballast need to be held down at all?
The blocks hold up the 2:1 slopes in both cases. They are also key to getting the heights right. Nothing is being held down! You need to look at the CN drawing online.