Track centers on turnout return curves?

[Chris750]

I am reading a manual put out by CN rail about turnouts and such for industrial rail and on one page they have "turnout return curves" which shows a #8 turnout with the straight track and diverging track On the turnout they have "track centers" and then 13', 13-6", 14', 14-6" and 15'. The only thing I can think of is this is the distance from the center of one track to the center of the parallel rail but I am unsure. And if so, why would the tracks have different distances between them for the same turnout? For example, why would you build a #8 with 13' between tracks, and then a #8 with 15' between tracks?

It doesn't matter which turnout they show (8,10,12,20) they all have the TC and same measurements.

Thanks.

 

[DaveL]

I just hate being a Smarty, but........

I just Googled "turnout return curves" and the spacing you refer to is between the main and the siding AFTER the siding curves back to parallel the main line.

DaveL

FWIW...I also learned a new RR term. I had never seen "turnout return curve".

 

[Chris750]

I can't find anything in google that talks about it and I did another search (I hate google). Can you post a link?
I hope I don't get in trouble for posting this image from their PDF.

 

[DaveL]

Methinks this will do the trick.......excellent information !!

DaveL

http://www.templot.com/martweb/mintut1a.htm

 

[Pencil42]

The only thing I can think of is this is the distance from the center of one track to the center of the parallel rail but I am unsure.

Yep, that's correct.

And if so, why would the tracks have different distances between them for the same turnout? For example, why would you build a #8 with 13' between tracks, and then a #8 with 15' between tracks?

You've got it backwards. Railroads have differing track centers for various reasons, including the speed, intended usage, even when the track was laid. That diagram is showing how to put a switch between two parallel tracks, and is giving the dimensions for each of the standard centers they use. So, if you have two tracks on 15' centers and want to put in a #8, they give the dimensions. If you have parallel tracks on 13' centers and want to put in a #12, they give the dimensions for that also.

 

[Chris750]

I just found that in a BNSF turnout PDF, they show it for high speed with the arrows between the track centers and a space of 16-5". Using the above make the turnouts look very nice, I also use this too:

By using the point length, length and limits of turnout and calculating the angle of F (#8 = 9', #10=8', #12=8', #15=8', and #20=6') I can get realistic turnouts easily without a template. I now also use the first document to gentlely bring the turnout into the parallel track using the distances shown at A,B,C,D etc.

 

[BuilderBob]

The table tells you this:
For a 13' track centre, a No. 8 turnout extended for distance X (35' 10") from the frog will create a track centre of A (4' 6 1/2"). That point (BC) is the start of the return (Begin Curve). The return curve is defined by B at a further 25', C at a further 25' and D at a further 10' 0 1/2". That point (EC) marks the end of the return (End Curve). The actual return (BC to EC) is the same curvature for a particular size turnout for any track centre - the distance X (not the curvature of the return) controls the resulting track centre.

For other turnouts the number of 25' steps and the size of final step varies, but because the measurement points are standardised at 25', then the track centres at those points are unique to each turnout. The result is that the curvature of the return matches the curvature of the diverging rail at the turnout.

 

[Chris750]

The table tells you this:
For a 13' track centre, a No. 8 turnout extended for distance X (35' 10") from the frog will create a track centre of A (4' 6 1/2"). That point (BC) is the start of the return (Begin Curve). The return curve is defined by B at a further 25', C at a further 25' and D at a further 10' 0 1/2". That point (EC) marks the end of the return (End Curve). The actual return (BC to EC) is the same curvature for a particular size turnout for any track centre - the distance X (not the curvature of the return) controls the resulting track centre.

For other turnouts the number of 25' steps and the size of final step varies, but because the measurement points are standardised at 25', then the track centres at those points are unique to each turnout. The result is that the curvature of the return matches the curvature of the diverging rail at the turnout.

Awesome, thanks. I was doing it right but I didn't catch on to all the annotations like BC = begin curve.