I am following the illustration on page 116 of John Armstrong’s Track Planning for Realistic Operation. Got all the lines drawn correctly but have a question. What does the tangent line and the arc line represent ? I believe it’s the inside rail of the track and that I would have to add about 3/8ths inch to the radius to get the centerline of the track, as figure 7-1 shows on page 84 . I want to make a template and use it to trace on the subroadbed but want to line it up with the centerline of the tangent. I’m in ho and I’m using a 24 in. radius. Any thoughts?
My copy only has 100 pages! But if this is the same picture I have the white line is their “strip wood” or “rail Batten”. The tangent being slightly off to one side just represents its thickness, so the inside of the white line is represents the center of the track. Notice where the radius meets the tangent at point M. That is radius is R + X which represents the center of the track if there were no easement.
I’m not home right now, but I agree that the lines represent centerlines. I’ll look at the pic later and see if I can shed any more light on your question.
The tangent line is the centerline of the incoming track. The leftmost black line is the offset radius, in the end I don’t think it is really used. The inner black line is the centerline you are going to end up on, with your desired radius but offset by X, which is where the space for the easement comes from. The batten is layed down with an edge on the centerline, and pinned into place at the points shown in the picture. So the centerline of the track is going to end up on the right (inside) edge of the white line in the picture.
Kudos to you! I studied that page and didn’t have the patience (or the motivation) to plan my easements that way. I used easment templates from Model Railroader.
http://www.trains.com/mrr/default.aspx?c=a&id=290
I printed and cut out the template then used it to lay out my easment with push pins and a pencil. The paper held up well enough after repeated use as I only had a half dozen easements to lay out.
“Texas Zepher” and others are correct, the lines represent track center lines.
I use John Armstrong’s easement method myself. It isn’t at all difficult, but instead of laying it out out fresh each time, I made illustration-board templates for easements into the curve radii I use most. Whenever I want to lay out an easement into one of those curves, I just trace the appropriate template.
If I’m doing parallel tracks, such as a double-track main line or a curved passing siding along a single main, I use the template to lay out the easement for the inner curve, than space the other track from that by whatever track center distance I want to use.
Good luck,
Andy
I was thinking, and thought I’d add a little:
The outer black line (the R+X radius curve) shows the space you need to add the easement. You might say, then why don’t I just use that radius? The answer is that the sharper curve with an easement is actually better operationally than the slightly broader curve. The abrupt transition into the curve is the problem, and the easment is what reduces this problem.
Using flextrack you can really do this without templates, just draw the R curve (with the center R+X from the tangent, as in Armstrong’s drawing), anchor the track at the start of the batten in Armstrong’s method, and flex smoothly to join up with the curve you drew at the point the batten matches the curve. That should give you ‘good enough’ without pulling out too much hair!
I built my own templates like Andy suggested. I built mine for double track by measuring the inner radius, easement and tangent (with marks so I knew where each transition began), and then made the template 1-1/4" wide, which are my N-scale track centers. So, when I lay the template down on the outside of the inner track center, it also marks the inside of the outer track center.
Templates make a lot of sense if you are using a lot of the same curve. In my planned layout I don’t really even know what the radiuses are (I could get them, but they are all different) as I drew it using flextrack in XTrkCad. Since it automatically adds the easements, the full sized printout does all the work (were that only true!). One thing to remember is that in most cases we are just getting an approximation of the ideal, but it is plenty good enough.
Thanks for the help. If I understand this correctly the radius is measured to the center of the track, not the inside rail, as I first thought. now it makes sense, thanks again.
You’ve got it!