Fast Tracks

Model Railroading Discussion Forums

Return To The Fast Tracks Website

The Fast Tracks discussion forums have been closed. Click Here for more information.

It is currently Tue Nov 21, 2017 12:26 am

All times are UTC - 5 hours [ DST ]




Forum locked This topic is locked, you cannot edit posts or make further replies.  [ 9 posts ] 
Author Message
PostPosted: Wed Aug 27, 2014 11:24 am 
Offline

Joined: Tue Sep 02, 2008 2:31 pm
Posts: 33
I'm building a slightly complex set of turnouts and so I printed some templates and taped them down to poster board in attempt to plan the whole thing and have something to work against. I very carefully lined them up and taped them down, but then I did some check measurements and found out I was way, way off.

A generic answer would be great, but a specific one would also be fine. I am building N Scale FastTracks #12 turnouts, in a simple arrangement to connect two tracks, like so:

Image

My question is, if the track centerlines are 1.5", how long should the crossing segment be, ideally via some easy to measure point on the turnout? Frog point to frog point would be great. End of quick sticks to end of quick sticks would work.

Basically after I hand laid that out the differences in my "looks perfectly straight to me" by eye layout were 0.75" across several of these! I can make them all the same, but if I am going to that trouble I should make them right so the segment between tracks is properly straight.


Top
 Profile  
 
PostPosted: Thu Aug 28, 2014 1:01 pm 
Offline

Joined: Tue Sep 02, 2008 2:31 pm
Posts: 33
I took a stab at this, can someone check my math?

http://www.ufp.org/~bicknell/nscale/TurnoutGeometry.pdf

Basically it looks like:

d= linear distance frog to frog I want to know
a= angle of divergence (this requires it to be the same on both turnouts)
c= center line to center line distance
g= gauge of track

The result is:

d = (c - g - (g / cos(a))) / sin(a)

Putting the values for a FastTracks N Scale #12 into the formula, it becomes:

(1.5 - .36 - (.36 / cos(4.76 degrees))) / sin(4.76 degrees)

And dumping that into Wolfram Alpha gives a result of 9.385 inches.

Giving that a eyeball with my ruler, it looks good.

Note that this assumes that from the frog on the rail is straight, which I understand is the case with FastTracks geometry but may not be the case for all switch types that exist in the world.

Does that look right?


Top
 Profile  
 
PostPosted: Thu Aug 28, 2014 3:10 pm 
Offline

Joined: Tue Sep 02, 2008 2:31 pm
Posts: 33
A valiant effort, but wrong. I printed out a template with these dimensions as well as a end-of-quicksticks line I calculated, lined them up, put down the ruler, and was clearly off.

Image

I'm wondering if I missed a width-of-rail issue, but the theoretical point of the turnout is a point, so I'm not quite sure where that would be...


Top
 Profile  
 
PostPosted: Wed Oct 08, 2014 2:03 pm 
Offline

Joined: Thu Nov 21, 2013 2:38 pm
Posts: 2
Location: Phoenix (metro area) Arizona
I drew two N Scale FastTracks #12 switches fixed at 1.5 inches center to center in Anyrail and came up with a straight connecting rail of 6.43 inches. Admittedly this is not a concise method for doing this calculation but it works in practical applications.

_________________
Mark


Top
 Profile  
 
PostPosted: Wed Jun 03, 2015 2:12 pm 
Offline

Joined: Tue Sep 02, 2008 2:31 pm
Posts: 33
I'd really like to know the proper math on this, and would be happy to turn it into an Excel and give it to our hosts so their customers could do the math in any scale for any turnout size.


Top
 Profile  
 
PostPosted: Wed Jun 10, 2015 11:01 am 
Offline
User avatar

Joined: Sun Sep 19, 2010 6:05 am
Posts: 51
Location: Rotterdam
As far as I know the only "point" you can use is the centrelines at the height of the frog. These centrelines crosses each other at the angle deriving from the point number. The crossing point is called "the mathematical point", but this is somewhere between the pointblades and the frog.

From the tip of the pointblades to a point short of the frog is a curve. From shortly before the frog till shortly after the frog is, in principal, a straight line.

I could not quickly find a quick and dirty method for translating a physical point dimension to a schematic approach. If I come across a method in the older books I have I will let you know


Attachments:
2015-06-10-HW-11-PB.JPG
2015-06-10-HW-11-PB.JPG [ 243.42 KiB | Viewed 1499 times ]

_________________
Paul Bender

Everybody can shovel, firing is an art

Image
Firing this train was more fun then hard labor :-) © R. de Water
Top
 Profile  
 
PostPosted: Wed Sep 30, 2015 9:04 pm 
Offline

Joined: Tue Sep 02, 2008 2:31 pm
Posts: 33
I think this page has the right formulas, but I have to wrap my head around it...


http://mysite.du.edu/~jcalvert/railway/turnout.htm


Top
 Profile  
 
PostPosted: Fri Oct 02, 2015 8:29 am 
Offline
User avatar

Joined: Sat Aug 13, 2005 10:48 am
Posts: 365
Location: East Texas - USA
The frog is not at a ratio height from the tangent . . . the frog is an isosceles triangle measured asymmetrically. This will complicate the math of location. (The frog location will be further from the points, lengthening the turnout lead.)

-ed-

_________________
-ed mccamey-
COSLAR RR - http://www.coslar.us/
NMRA Standards and Conformance Department
PROTO & FINE Scale Coordinator
I estimate I have about 5 pounds of coupler springs somewhere in the vicinity of my workbench.


Top
 Profile  
 
PostPosted: Thu Oct 15, 2015 5:07 pm 
Offline

Joined: Tue May 29, 2007 12:20 pm
Posts: 100
Location: Oklahoma City, OK
I printed some #12 turnout templates and when laid out at 1.5" centerlines, I get about 13" length from frog point to frog point.

That is crossing rails to get point to point, but does give you a reference point.

Not sure my method is correct, but everyone is coming up a little different. :shock:

_________________
Kurt Konrath

SP was king of the road, Cotten Belt will run forever! D&RGW will rule the hills!


Top
 Profile  
 
Display posts from previous:  Sort by  
Forum locked This topic is locked, you cannot edit posts or make further replies.  [ 9 posts ] 

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group