Fast Tracks

I am decent with math but I cannot seem to get it concerning turnout measurements. I understand the part about the 1 unit over x "X" units of length = turnout size. What I don't understand is how to figure it so it works on HO turnouts. Here is what I come up with:

Using the rail gauge as 1 unit and multiplying it by the # of the TO I cannot make it match the turnouts I am making, using Fast Tracks fixtures. I am sure all the good methods for whoever makes TO's by whatever fixture or guide come out to the same size.

Thus: using HO gauge at .6494" NMRA min. spec. x 8 (#8 TO) = 5.195". The #8 I measured actually was 8.750" from the frog point to the point rail point on the diverging rail with the HO gauge at .657 or so.

Inversely: 8.750" divided by .649" = 13.48". Would this make it a #13-
1/2 turnout? Or are the dimensions used set by NMRA even if they do not match real world numbers?

I even used the 4' 8.5" (I hope this is correct) real rail gauge. Multiplying this by 8 = 37.367' (37' 4") for a real world #8 TO frog-to-point length. This method produced the same frog-to-point length of 5.195" in HO scale.

Where am I missing it? I just want to know, I am not going to try to change the world.

UPDATE added after original info above:
I think I may have found the discrepancy in my calculations and thinking. The frog point-to-closure rail point is the wrong place to measure? In looking closer at the NMRA spec sheet a "light" came on. The measurement is actually taken from the frog point back. (Away from the closure points). Using this makes the measurements work. You could really make the point rails any length you wanted to and a #8 would still be a #8. The NMRA standards show the point rails to be 9" for a #8 but the measurement is taken from a theoretical frog point location which is just behing the actual frog point (where I measured the 8.750").

Hope I haven't confused anyone, but it makes sense to me now.

I find this interesting just because I find it interesting. I think what your conclusion (which I agree with) says is that the key is the angle of the frog. The point rails divirge from the stock rails at a smaller angle, and then curve to the frog angle (at least part of the way), so the distance from the frog back to the points will be longer than if the points left the stock rails at the frog angle, which is what you found when you measured. I need to think some more......

The 1:X turnout only reflects the FROG point rails angles and has nothing to do with the frog point to the switch point distance (the lead). The lead is a geometric function that includes the closure rail radius and Co-Sine of the frog angle. The point of intersection (theoritical) will be about 2/3 the distance of the turnout lead. If you want to really get into turnout geometry and the math, there are two good calculator programs available. One is an actual commercial calculator in programatic form and the other is a very nice and complex spreadsheet.

Templot is the commerical program and is very extensive.

The Spreadsheet is one developed by Horner. This can be downloaded from the web.

These are widely referenced in the yahoo e-lists and a good search will find them easily (mine are now on my system hard disk and I can't recall the actual links).

_________________
-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.

Took just a minute to locate:

David Honner's excellent Excel spreadsheet -
http://www.urbaneagle.com/data/Turnout_Calculator.zip

Martin Wynne's Track Design Software -
http://www.85a.ision.co.uk/index.html

_________________
-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.

Thanks for the information lead. I downloaded it. I am familiar with Excell so I should not have a problem using it. My main objective is to learn as much as I can about something that interests me.

I downloaded and tried out the turnout calculator spreadsheed in Excel. It loaded OK but I need to go thru it carefully to learn it. It has to have a CAD program to make printouts. Any recommendations, good but inexpensive, on a program? I have a house planning CAD type program, haven't checked it yet. Also, what kind of a printer? Hope it doesn't take a plotter! They are ExPeNsIvE!!

What/how would I get the CAD program to use the Excel info?

Thanks for the help.

I use the cad program called 3rdPlanit. The turnout calculator excel program provides four values that are used to customize standard turnouts inside 3pi. It is much easier to modify an existing straight turnout by changing a few parameters. Custom curved turnouts are another story. They are really a matter of trial and error.

One method for curved turnouts is to scan the actual piece. Import the image into 3rdplanit. Then lay a turnout on top and modify the parameters until it matches. Very tedious.

You could take the Fast Tracks pdf files, save them into a jpg format and then import into 3rdplanit. 3rdPlanit can import dxf and csv files. If we could get a centerline drawing for the Fast Tracks fixtures, you could import the dxf file and get an approximation of a turnout with line segments. It wouldn't function like a turnout when running trains inside 3pi, but maybe that doesn't matter.

Here is a link to the 3rdPlanit program website.
http://www.trackplanning.com/

Here is a link to files created by 3pi users.
http://3pi.mrld.info/superark/