Large Scale Central

Track plan

Track and Trestles
#81

Devon Sinsley said:
Steve’s picture and explanation leads me to believe that the transition from curved to straight begins just before or right at the convergence of the two rails at the frog.

A #7 frog is going to be a different length than a #20 frog, so I would think that the transition starts at the end of the frog casting. The frog (however long) is as straight as possible, and the closure rails leading to the frog curve at a specific ratio that relates to the point rail length (those stay straight), and the frog angle.

#82

Devon Sinsley said:

Craig Townsend said:

Devon,

Maybe this will help you visualize the different turnout lengths, point lengths, and frog lengths. I thought about building a #22 turnout just to see how big the sucker is…

None of this clearly shows where the transition from curve to tangent begins. It shows lengths of various pieces in relation to the various frog angles but not the point at which curve becomes straight. Lets just take the #20 above. Does curved track transition to straight 1 foot, 2 feet, 15 feet prior to reaching the frog point?

But in our scale, does it really matter? For all intents and purposes, it is a gentle curve, that may, or may not, become a tangent, a short distance before the frog. To get the answer (and, I too, am curious), we’ll have to ask a civil engineer.

#83

Look at this #9 frog. To me it doesn’t look like any point of the frog is curved prior to the point of the frog. Here’s my guess on why the frog remains entirely straight; because you can use it for a right or a left hand turnout. If the frog had a slight curve on one side, that would only allow that particular frog to be used as either a left or a right turnout. So I would say that the tangent starts immediately after the frog casting.

#84

With all this discussion about turnouts, Devon’s going to be measure track curves in chords instead of diameter… (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)

#85

See, now Devon is asking kind of the same thing I was asking. The closure rail (traveling from the frog to the point) begins its curve when/where? If the closure rail ran straight for a long enough distance, then the point would really jar the wheels from straight to a path leading straight to the frog. A few pages ago I was asking about the curvature of the closure rail and here we are again. If the closure rail starts its curve right at the frog casting, then I understand how the length of the closure rail/point is figured out. If not, then I am still in a fog.

Craig, I understand the the frog is straight, and the stock rail is also straight opposite the frog. Its the closure rail curving from the frog to the tip of the point that I, and believe Devon, are a bit lost on.

#86

Craig Townsend said:

With all this discussion about turnouts, Devon’s going to be measure track curves in chords instead of diameter… (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)

Or in degrees, which I only just understand, but cannot recite.

#87

David Maynard said:

See, now Devon is asking kind of the same thing I was asking. The closure rail (traveling from the frog to the point) begins its curve when/where? If the closure rail ran straight for a long enough distance, then the point would really jar the wheels from straight to a path leading straight to the frog. A few pages ago I was asking about the curvature of the closure rail and here we are again. If the closure rail starts its curve right at the frog casting, then I understand how the length of the closure rail/point is figured out. If not, then I am still in a fog.

Craig, I understand the the frog is straight, and the stock rail is also straight opposite the frog. Its the closure rail curving from the frog to the tip of the point that I, and believe Devon, are a bit lost on.

In the drawing of the frog that Craig has so generously provided us, above, part of the casting extends to the left of the vertex of the frog. I don’t say point, to avoid confusion, but that is what it is. That portion to the left of the vertex of the frog from the beginning of the closure rails, and, as part of the casting of the frog, are necessarily straight, so that the frog casting can be used for either a left or right hand turnout. The curve of the closure rail likely begins where the casting ends.

#88

David Maynard said:

See, now Devon is asking kind of the same thing I was asking. The closure rail (traveling from the frog to the point) begins its curve when/where? If the closure rail ran straight for a long enough distance, then the point would really jar the wheels from straight to a path leading straight to the frog. A few pages ago I was asking about the curvature of the closure rail and here we are again. If the closure rail starts its curve right at the frog casting, then I understand how the length of the closure rail/point is figured out. If not, then I am still in a fog.

Craig, I understand the the frog is straight, and the stock rail is also straight opposite the frog. Its the closure rail curving from the frog to the tip of the point that I, and believe Devon, are a bit lost on.

The closure rail curves from where it connects to the frog to where it connects to the point rail. When I look at the NP engineering drawings for my #9 turnout, the points are listed as 16’ 6" long with no curvature, and the closure rail is listed at 597’ 11 25/32" radius of curve and a 9 degree, 35’ 34". On the drawing it shows the “P.C. of Turnout Curve starting at the end of the 16’ 6” point rail. The length of the points varies with the size of the turnout. The #7 turnout only has a 10’ 0" point rail.

#89

This is not the best photo of the drawing, but it shows the whole turnout. The individual rail pieces are the following; frog, closure rail, point rail. On the model, we tend to combine all together into one continuous piece of rail so the line between where the point rail ends, and the closure rail begins is quite often blurred.

#90

In an effort to clarify this, here’s the link to my Google Drive for the PDF that had both the #7 & #9 turnouts. Now there’s 29 pages of different turnouts, but they are mostly the same 16’ 6" point rails, and mostly #9 frogs. The difference being the type of frog, and the rail size. Is this a case where a 1000 words can’t explain one picture?

https://drive.google.com/file/d/0Bz7qtokb4MjUdzBKY0JIaUJmMUk/view?usp=sharing

#91

So, is the “point rail,” a separate piece of rail, bolted on to the closure rail? Or is it where the machining of the points occurs?

#92

The closure rail curves from where it connects to the frog to where it connects to the point rail. When I look at the NP engineering drawings for my #9 turnout, the points are listed as 16’ 6" long with no curvature,

Ah ha! Ok, now I am getting it. I knew that the closure rail and the point rail were not a continuous curve of the same degree. Now that explains what I was missing there.

Steve yes, I know the frog casting is straight, on both routs. I had that part from page one. It is figuring out the curve of the closure rail, and where it curves, that had me a bit baffled.

#93

Steve Featherkile said:

So, is the “point rail,” a separate piece of rail, bolted on to the closure rail? Or is it where the machining of the points occurs?

Separate piece bolted to the closure rail. The point rail isn’t machined the whole length either.

#94

I feel a road trip coming on in my immediate future.

#95

Steve Featherkile said:

But in our scale, does it really matter? For all intents and purposes, it is a gentle curve, that may, or may not, become a tangent, a short distance before the frog. To get the answer (and, I too, am curious), we’ll have to ask a civil engineer.

Now I do believe this is the correct modeling answer. I mean they do make toy switches that curve through the frog and they do work. So I would think that if it was straight through the frog but then started to curve immediately from that point to the throw rod we wold be ok. Just like I am sure that there is some fancy way for determining the ratio at which the curve goes from sharper to almost straight at thepoints if we just wing it and make it close to what we see in a prototype we would be ok.

But like I said several times in modeling I like to learn about the real thing. I could just build one without understanding it and make it work. But I would like to understand it.

Just think a few days ago I didn’t really even understand a frog or a #'ed switch now I asking tough questions. See I am getting it.

#96

Craig Townsend said:

With all this discussion about turnouts, Devon’s going to be measure track curves in chords instead of diameter… (http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)

This is generally how this goes with me. And I get what your saying about the straight frog. I would agree that the entire frog is straight. Your reasoning makes sense but I also believe that in order for the wheels to run true they would need to run straight.

So when does the straight give way to the bend. Same question. At the point that the rail attaches to the frog?

#97

Heck, I’m learning a lot of stuff I didn’t know a few days ago.

#98

Steve Featherkile said:

Heck, I’m learning a lot of stuff I didn’t know a few days ago.

Now I ask you the same question. Aren’t you glad I asked? I for one have probably come the furthest but I certainly understand switches better than I ever thought I would. I am glad through my thick headedness David and Steve were able to learn and we challenged Craig to explain his self. ( I think it is good for a person to be forced to explain what they know).

#99

Devon Sinsley said:

Your reasoning makes sense but I also believe that in order for the wheels to run true they would need to run straight.

This is why the wheels have a fillet on the flange. The part of the wheel that rides on the rail is tread + fillet. As a wheel enters any curve, the fillet of the flange rides differently.

http://www.thenakedscientists.com/HTML/experiments/exp/train-tracks-how-trains-go-round-corners/

I think our discussion of curves is related to turnouts, but I don’t think that turnouts have easements in and out of the curve of the closure rail. The reason I say this is because certain turnouts have certain speed restrictions. For example a #9 turnout wouldn’t be seen on a mainline, but rather a #20 or higher. The sharper the turnout number (and thus the sharper of the closure rail) the slower the speed.

I feel like I’m getting deep into the weeds with this conversation!

#100

Devon Sinsley said:

Steve Featherkile said:

Heck, I’m learning a lot of stuff I didn’t know a few days ago.

Now I ask you the same question. Aren’t you glad I asked? I for one have probably come the furthest but I certainly understand switches better than I ever thought I would. I am glad through my thick headedness David and Steve were able to learn and we challenged Craig to explain his self. ( I think it is good for a person to be forced to explain what they know).

This thread is getting to the limit of what I know myself. But I’ll say one thing, quit calling them switches! The whole thing is called a turnout, the part that actually moves is called the points, which is moved by a switch machine. So when your working the ground, you say get the switch, not get the turnout. When your talking about track design/structure a switch is just a tool to move the points of the turnout.