How is track diameter calculated

[Gizzy]

ah R5 is too big i need piko R3 (which is diffirent from LGB r3)

Piko R3 curves will fit nicely inside LGB R3 curves should you want double track….

 

[NorthwestGarrattGuy]

Piko R3 curves will fit nicely inside LGB R3 curves should you want double track….

i cant really squeeze anything bigger than piko R3

 

[Gavin Sowry]

Print these out and use as a template they are for R5.
I use flex track rail and make sleepers/ties from ripped up treated pine boards.

Beware the fundamental flaw on those plans. They are calling it a #5, but are showing a tangential spread for a 1 in 5 turnout.
With a #5, the right angle should be from both legs of the frog, intersecting at a point which is a projection of half the angle of the frog.

 

[GAP]

Beware the fundamental flaw on those plans. They are calling it a #5, but are showing a tangential spread for a 1 in 5 turnout.
With a #5, the right angle should be from both legs of the frog, intersecting at a point which is a projection of half the angle of the frog.

I used the drawings as a template for the rail lengths and layout and that works for me.
I haven't made any smaller but I am looking at building one with a 1" divergence 3" from the point to replace an LGB R1 that is to tight.
Hopefully that will work.

 

[Greg Elmassian]

Where is the flaw? I see where it says 1" divergence 5" from the point (of the frog), that is the definition of a #5.

Greg

 

[Gavin Sowry]

Where is the flaw? I see where it says 1" divergence 5" from the point (of the frog), that is the definition of a #5.

Greg

There are two recognised ways of measuring the divergence. The way shown on that plan is known as the tangential method, as in 1 divided by 5 equals the tan of the angle of the frog. The other method is the intersection method, whereby each leg of the from is measured at right angles to the 5 units, and the angle is 2 times the tan of half the angle.... which is not the same as tan of the full angle in the first method. The intersection method is very American, the tangent measure British. The authoritive book 'British Railway Track', published by the Permanent Way Institute, goes to pains pointing out this difference.
Without having reference books at hand, you will find that a 1 in 5 frog angle is not the same as a #5... I learned, and got told in no uncertain terms about this when I was starting out in Track (50 years ago) and erroneously used AREA data tables, instead of our own (British derived) standards.

 

[Greg Elmassian]

Ahh, so British frog numbers are different?

I'll have to read up, but most US people read as frog number, they don;t usually calculate or specify the angle in degrees.

I'll have to read up on this... in our hobby, it would be interesting to see if there is a significant difference in frog number using the 2 different methods.... angle in degrees I get, but most frogs specified by number are rough calculations where I wonder if the different measuring methods would result in significant differences.

Greg

 

[Gavin Sowry]

Ahh, so British frog numbers are different?

I'll have to read up, but most US people read as frog number, they don;t usually calculate or specify the angle in degrees.

I'll have to read up on this... in our hobby, it would be interesting to see if there is a significant difference in frog number using the 2 different methods.... angle in degrees I get, but most frogs specified by number are rough calculations where I wonder if the different measuring methods would result in significant differences.

Greg

And, to make things even more interesting, there is a prototype practice for having 'radius' frogs. Germans, apparently have used that method... at least, that's what the recently deceased Iain Rice told me when we had a chat about turnouts one time when I met him.

 

[Greg Elmassian]

Yes, I will have to use your term, I have used "curved frogs" as a term, but yours is better. You don't see it here, although I would suspect in mining track or some narrow gauge in a switch yard it must have been done.

I completely understand why LGB did it, with the uber tight curves, you need a switch to be able to exactly replace a curve in the diverging route.

Anyway I will research what you posted, I'm "getting" the math, but right now it seems that the frog number is probably the same from a practical sense with either method once rounded to a whole number in our model case.

If you have a link handy for me to read it would be appreciated.

Greg