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curved turnout frog number ?

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Posted by rrinker on Friday, November 23, 2018 3:13 PM

 The thing the CAD can do is make sure the tracks extending off any of the turnout legs matches the radius, instead of possibly being kinked or not exactly matchng because the sectional track piece is 18" radius and the turnout is 18.4" radius.

 Frankly, if I couldn;t get accurate dimensions of certain brands of track peices, I wouldn't use them, and go for an alternative method, such as a pinwheel ladder made with Atlas #4, which are really a 4.5 frog, ok for switchers and smaller cars. If I had to make my yard that compact, I'd forget all ideas of long cars.

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Posted by railandsail on Friday, November 23, 2018 7:43 AM

rrinker

 Best they can do is match whatever the manufacturer says the specifications are. If the manufacturers misstate their dimensions, well... but they generally aren't off by a huge amount, which means if you don't try to squeeze in ever last fraction of inch, the plan will still fit as drawn in the CAD program.

I've found (as well as others) that these 'mis-stated curve radii' by the manufacturers are sometimes CONSIDERABLE different than real life.

And as GregC has mentioned somewhere on one of these discussions of curved turnouts, the placement of these turnouts is MORE CRICTIAL than the placement of ordinary turnouts due to their double curves whose connections with other tracks can be thrown off considerable from drawing phase/computer design verses actual model layout real life (I think I said that somewhat correctly?,...I could not find his quote).

Yes, I am trying to cram a lot of trackage into my freight yard/ladder design, but don't real railroads attempt to do the same?

                        

 

 

 

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Posted by rrinker on Thursday, November 22, 2018 7:34 PM

 Best they can do is match whatever the manufacturer says the specifications are. If the manufacturers misstate their dimensions, well... but they generally aren't off by a huge amount, which means if you don't try to squeeze in ever last fraction of inch, the plan will still fit as drawn in the CAD program.

                                   --Randy

 


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Posted by railandsail on Wednesday, November 21, 2018 7:41 AM

RR_Mel

I agree with Carl, I worked up a Peco curved turnout on my CAD a few years ago and couldn’t come up with their specs as printed.  I’m glad I bought the turnouts before I did the drawing otherwise they wouldn’t have fit my CAD driven track work.
 
Mel
 



That was a point I brought up in another subject thread I started on curved turnouts before I discovered this one today,....how do these 'exacting' trackplan softwares deal with nuances of curved turnouts,...(perhaps they are not so exact in some cases?).

I'll have to have a look back thru these discussions at a later date. Appears to be a really educated discussion of the subject, but a little above my pay grade at this time (above my understanding). 

 

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Posted by gregc on Wednesday, November 21, 2018 5:03 AM

gregc
i'm working on laying out a curved turnout and I come up with larger frog numbers than the commercial turnouts of the same sizes.   Do commercial turnouts use stock frogs?

i believe the diagram illustrates how a curved turnout can be made relatively short and with more typical frog numbers by laterally offsetting the centers of the curves. (thanks DaveB)

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Posted by gregc on Sunday, November 4, 2018 5:39 AM

rrinker
The angle to frog number formula is angle = 2 arctan (1/2x) where x is the frog number, and that is anything BUT a linear function.

yes.  the relationship between frog number and angle is non-linear.

rrinker
Not so sure it should?

presumably this is referring to my comment to

gregc
The Catskill site describes prototypical methods which i believe describe a constant radius closure rail from points to frog.  

the following figure (posted yet again) illustrates how a #6 (or any) turnout can have different lead lengths and closure rail radii.  The blue line indicates a constant radius curve and the red line a straight section of rail.   number at left is closure rail radius and middle number the lead length.

 

The Catskill site has a single set of equations for determining the lead length and closure rail radius where the closure rail radius is constant up to the frog for a specified frog #.  This means the tangent line of the closure rail is aligned and parallel with the frog where it meets the frog.

I don't believe a prototype would do it any other way except in a special case.

while a shorter turnout with a #6 frog angle may be necessary in a special case (e.g. industry spur), the drawback is a tighter closure rail radius which may limit the locomotives that can handle that specific turnout.

 

RP 12.31 specifies a #6 turnout lead length of 6.5" for which the shortened closure rail radius is 30".   I'll guess that this was a pragmatic compromise; a shorter turnout and a 30" radius that is more than adequate for most modelers.

But, as the following figure illustrates, a properly laid out #5 turnout has a closure rail radius of 33" and is just a bit longer, 6.6", than an RP 12.31 #6 turnout.

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Posted by gmpullman on Saturday, November 3, 2018 9:16 PM

 

 

gregc

engineers often use less time consuming approximations that are "good enough".

 

Well, I don't know if this will help or hinder the discussion but I'll toss it out for your perusal:

 ICS_frog_33 by Edmund, on Flickr

 ICS_frog_34 by Edmund, on Flickr

 ICS_frog_35 by Edmund, on Flickr

 ICS_frog_36 by Edmund, on Flickr

 ICS_frog_37 by Edmund, on Flickr

 ICS_frog_38 by Edmund, on Flickr

 

If you're not put to sleep yet, I can post the chapter on crossovers, too.

Regards, Ed

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Posted by rrinker on Saturday, November 3, 2018 6:43 PM

 Not so sure it should? The angle to frog number formula is angle = 2 arctan (1/2x) where x is the frog number, and that is anything BUT a linear function.

                            --Randy

 


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Posted by gregc on Saturday, November 3, 2018 12:57 PM

thanks. 

I wasn't aware that the RP had been updated in 2015.  My notes are from 2014.

while the rp 12.31 values are better(?) than the rp 12.3 values from 1961, i still see inconsistencies from frog # to #.

the lead length doesn't increase proportionally (nor exponentially) (see jumps between #6 and 7 and #10 and 11).

I don't understand the value of what they call the "curved rail radius (11)" which I assumed means the closure rail and is shown in red, drawn to the frog.  It doesn't seems to align with the frog and alignment varies from # to #.

I haven't figured out what the ordinate points are referring to.   They didn't line up with the curve rail radius.   And the RP specifies a section of straight track.  Any section of straight track will reduce the closure rail radius.

The Catskill site describes prototypical methods which i believe describe a constant radius closure rail from points to frog.  

 

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Posted by rrinker on Saturday, November 3, 2018 11:31 AM

 Are you looking at the correct specs? If you go to the STandards and RPs sectioon ont he NMRA site, there's a ZIP file full of PDFs under RP13 which has individual PDFs for each scale in straight and curved turnouts. The HO one ate 12.32 for straight and 13.33 for curved turnouts, updated 2015.

 Manufacturer dimensions can and will vary - this is only an RP, not a Standard, so strict adherence to the numbers in the tables is not a requirement. 

                                --Randy


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Posted by gregc on Saturday, November 3, 2018 8:23 AM

this diagram illustrates the NMRA turnout dimensions described in RP 12.3 as of a few years ago (i don't believe the radius is correct, but the lead length (middle number) is accurate).

i hope you agree that there appear to be some inconsistencies

However, it looks like the NMRA has updated their spec, NMRA RP-12.2 Turnout Dimensions.     And while at least the lead lengths for the smaller turnouts appear more correct, there still seems to be some inconsistencies (easier to see graphically)

#4   6 13/16
#5   7  5/8
#6   8  3/8
#7  11  3/8
#8  12  3/16
#9  12 15/16
#10 13  5/8

 

when using equations from the Catskill site, the turnout dimensions change more consistently.

 

selector
 
gregc

 do all all turnouts have to be the same

From the frog point, yes.  The frog number is what matters, and the ratio of divergence AT the frog is the basis for the frog 'number'.

 

deviations in the closure rail, either an inconsistent radius or straight sections leading to the frog, can result in turnouts of different (lead) lengths.

while the frog # should be all that matters, it looks like model turnouts, including curved turnouts as discussed, have some deviations.   At this point, how can they meet NMRA specs when those specs seem to be changing?

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Posted by selector on Friday, November 2, 2018 6:34 PM

gregc

 

 
selector
A #6 frog diverges one unit toward the diverging route for every six units of length

 

let's make that unit 1/10"

see http://www.catskillarchive.com/rrextra/tkwk10.Html previously posted

do all all turnouts have to be the same

 

From the frog point, yes.  The frog number is what matters, and the ratio of divergence AT the frog is the basis for the frog 'number'.

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Posted by 7j43k on Friday, November 2, 2018 5:52 PM

I've noticed.

 

Ed

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Posted by gregc on Friday, November 2, 2018 2:56 PM

engineers often use less time consuming approximations that are "good enough".

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Posted by 7j43k on Friday, November 2, 2018 1:43 PM

gregc

it's called a limit.   But i'm determining the frog angle from the tangents to the curve where the rails intersect and calculating the frog # from the angle (see link posted above 3x).

 

 

Go ahead.  Do it the EASY way--the "engineering" way rather than the "mathematical" way.

 

 

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Posted by dante on Friday, November 2, 2018 1:10 PM

For what it's worth, I have many W/S curved turnouts in all sizes, most purchased in the last few years, and I offer the following info:

The published larger radius numbers are correct, but the diverging radius numbers are consistently 2" too high (e.g., 24/20 is actually 24/18).

The frogs are curved and there is no straight track segment after the frog. The curve is continuous, through the points, frog and beyond.

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Posted by gregc on Friday, November 2, 2018 12:57 PM

riogrande5761
So just curious, if a commercial turnout can be made to operate smoothly and reliably, what is the motifvation for handlaying?

i have a small layout.   I've hand laid all my track.   Trying to fix some awkward trackwork exposed since adding a new loco.   A true 22"/25" turnout would really be nice.   

I don't think it will be difficult but taking some planning.   working on a rail bender to make it easier.  Looking forward to smoother operation out of a siding.

7j43k
But as you make that distance smaller, the error shrinks.  You have now entered the land of integral calculus.  And, yes, you DO get a number.

it's called a limit.   But i'm determining the frog angle from the tangents to the curve where the rails intersect and calculating the frog # from the angle (see link posted above 3x).

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Posted by 7j43k on Friday, November 2, 2018 11:46 AM

Oh, yes.  The frog in a curved turnout does have a "frog number".  As you know, the frog number is derived from dividing the distance between the diverging rails into the length from the frog point to that chosen measuring point*.

With a curved turnout, that distance from frog point to measuring point is curved, and throws the frog number off.  But as you make that distance smaller, the error shrinks.  You have now entered the land of integral calculus.  And, yes, you DO get a number.

I got a C in that class 50 years ago.  That means I still remember enough to make my assertion, but not enough to show y'all the formula.  Lucky me.

 

Ed

 

*My personal (prototype) frog-measuring device is always with me:  my shoe.  I go out to the spot where my shoe length matches the rail spread.  Then I toe-to-toe back.  That's how I found that most SP industrial siding switches are #7.  Not #6.  Not #8.

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Posted by selector on Friday, November 2, 2018 11:42 AM

Handlaying permits closer tolerances, especially at the frog, which permits the use of closer-to-scale tires and flanges.  Tim Warris explains this in his very first ever posted video on his site.  If you don't mind Code 110 tire profiles and wheels dipping between the deflection of the closure rails and their adjunct guard wings and the gap to the frog point, then the commercial ones that don't have filling in that gap will still work.  But also the commercial turnouts have more variance and a slightly wider-than-true-gauge setting so that people don't routinely have to tweak the separations of flanges on all of their wheelsets...the turnouts will work with a probability of 95-97% regardless of the code of wheels sets...except for the close-to-scale ones.

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Posted by 7j43k on Friday, November 2, 2018 11:36 AM

One thing to keep in mind:

A reason that "regular" switches are designed with straight trackage through the frog area is to minimize lateral forces at that location.  Those lateral forces have a tendency to increase the liklihood of picking the frog (yes, it is impossible.......).  So with, say, a 20 degree crossing (note I am saying "crossing", not "switch") with straight track all around, you could pretty much roll right over it WITHOUT any guard rails.  Of course, no one's going to leave them out, because!

Because of the lateral forces in a curved turnout, it would make sense not to push the envelope in the frog area.  Put another way:  a curved turnout is not just a bent straight one.

I recommend trying to have the radius of the curves through a curved turnout be "gentle".  Especially the inner one.  Which is, of course, the tighter one.

 

 

Ed

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Posted by riogrande5761 on Friday, November 2, 2018 11:02 AM

this discussion has made me realize that perhaps the frog # of a curved turnout is irrelavent.

That is what I've been thinking as I read through this topic too and maybe why it's kind of pointless to get too tied to curved turnout numbers as labeled by manufacturers.  Again, why have looked more at radii as a point of reference.

I wonder if Fast Tracks has templates for curved turnouts so you don't have to engineer a home-made curved turnout from scratch.  That is definitely beyond my skill and attention level.

There are a number of roll your own turnout types at MRH, maybe that would be a good place to raise this discussion.

I'm trying to roll my own and am trying to reconcile the inconsistencies i read about with commercial turnouts

So just curious, if a commercial turnout can be made to operate smoothly and reliably, what is the motifvation for handlaying?  More accurate appearance?

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Posted by gregc on Friday, November 2, 2018 11:00 AM

Doughless
I think some of us are saying that calculating a frog # of a curved turnout won't compare well to a straight turnout,

this discussion has made me realize that perhaps the frog # of a curved turnout is irrelavent.

as I said above, the frog # of a standard straight turnout has a fixed closure rail radius and lead length.   again, rail radius limits the locomotive that can be used.   Lead length may be most critical in yard design.

so selecting a frog # captures those two parameters.

the frog # as I calculated it for curved turnout captures neither.   The closure rail radius is ideally the inner curve radius and the closure rail length (frog position) depends on both radii.

 

Doughless
are you trying to estimate the inner radius of a commercial curved turnout by calculating its frog #

the important thing for me was to locate the frog position on a curved turnout i plan to build.   I calculated the frog # to compare my calculations to commercial turnouts.   Based on comments in this thread, my understanding is commercial turnout radii are not accurate.

 

this discussion has given me an even better understanding of turnouts and an appreciation for the limits of commercial products.

thanks

 

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Posted by Doughless on Friday, November 2, 2018 9:11 AM

gregc

 

 
riogrande5761
So ultimately is this all academic?

if I don't want to roll my own,

 

Not for me.  I'm trying to roll my own and am trying to reconcile the inconsistencies i read about with commercial turnouts.

 

I think some of us are saying that calculating a frog # of a curved turnout won't compare well to a straight turnout, other than the lower the number the frog is, the tighter the inner radius will be.

I get your point about comparing to commercial turnouts, but are you trying to estimate the inner radius of a commercial curved turnout by calculating its frog #, or is there another way to measure inner radius?

Perhaps we see it a different way than how you're seeing it.

Carry on and good luck.

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Posted by gregc on Friday, November 2, 2018 8:54 AM

rrinker
a curved frog wouldn;t have an 'angle' since it's curved,

a frog is simply the crossing point of two rails.   I don't believe there is any requirement on length.

rrinker
Too shallow a frog angle (higher number) with diverging curves that are sharper than the substitution radius of an equivalent straight turnout, or the closure rail radius of an equivalent straight turnout, would be next to pointless, as who cares if the larger rigid wheelbase loco cna negotiate the frog if it can;t negotiate the tight diverging curve?

on a straight turnout, the frog is straight.   The curve radii is maintained on a curved frog.   I don't think there is any doubt that a loco can't negotiate frog if it can negotiate the closure rail

the figure with the multiple #6 turnouts posted above shows that there is a maximum closure rail radius in order to obtain the proper angle at the frog and that sharper closure radii are possible by having a straight section leading to the frog with the benefit of having a shorter lead length.

the frog number dictates the maximum closure rail radius and that radius limits the the locomotive.

rrinker
Reverse I think would be true as well, why have a #4 frog feeding 60 and 32" radius curves, if the loco can get though the curves but not the frog? 

how can it not get thru the frog as long as the closure and diverging rails are aligned with it? (see above re: closure rail limits)

rrinker
 If the frogs on commercial curved turnouts are curved - unless everyone agrees where to draw intersecting straight lines, any measurement of angle and thus frog number are somewhat subjective

simple geometry determines the point at which the two curved rails of different constant radii intersect.   The tangents of the curves at the intersection point determine a frog #.  (but are they constant?)

rrinker
if they can;t even agree to what the diverging rail radii are, and publish unrealistic numbers, good luck reconciling it all.

i already agreed that if the commercial turnout radii are not correct, a comparison is invalid.

 

i can see, as others have stated, how deviations from true curves, for practical reasons, reduces the length of the closure rail and hence the overall size of a commercial turnout.   Maybe it's irrelevant to discuss frog # with curved turnouts.   Isn't it the curve radii that matter?   But ignoring the deviations may lead to problems with long wheelbase locomotives.

fortunately, i don't have to live with those constraints.

 

The following table shows the frog location and # for curved turnouts that are from 1 to 4 inches different in radii based on the method I used to determine the frog position for the turnout I'm planning.   The smaller the difference in radii or the greater the radii, the longer the closure rail and higher the frog #

      rad0  rad1      x      y    a0     a1     da    frog
      18.0  19.0  17.39  12.22   71.6   68.7   2.9  # 19.7
      20.0  21.0  19.28  13.54   71.5   68.8   2.6  # 21.8
      22.0  23.0  21.16  14.86   71.4   69.0   2.4  # 23.9
      24.0  25.0  23.04  16.18   71.3   69.1   2.2  # 26.0
      26.0  27.0  24.92  17.50   71.2   69.1   2.0  # 28.2
      28.0  29.0  26.80  18.82   71.1   69.2   1.9  # 30.3
      30.0  31.0  28.68  20.15   71.0   69.3   1.8  # 32.4

      18.0  20.0  14.09   6.27   50.2   45.8   4.5  # 12.8
      20.0  22.0  15.58   6.94   50.0   46.0   4.1  # 14.1
      22.0  24.0  17.06   7.60   49.8   46.1   3.7  # 15.5
      24.0  26.0  18.55   8.26   49.7   46.3   3.4  # 16.8
      26.0  28.0  20.04   8.92   49.5   46.4   3.2  # 18.2
      28.0  30.0  21.52   9.58   49.4   46.5   2.9  # 19.5
      30.0  32.0  23.01  10.24   49.3   46.6   2.7  # 20.9

      18.0  21.0  12.17   4.29   41.6   36.1   5.5  # 10.4
      20.0  23.0  13.43   4.73   41.3   36.3   5.0  # 11.4
      22.0  25.0  14.68   5.17   41.1   36.5   4.6  # 12.5
      24.0  27.0  15.94   5.61   40.9   36.7   4.2  # 13.6
      26.0  29.0  17.19   6.05   40.8   36.8   3.9  # 14.6
      28.0  31.0  18.44   6.49   40.6   37.0   3.7  # 15.7
      30.0  33.0  19.70   6.94   40.5   37.1   3.4  # 16.8

      18.0  22.0  10.95   3.30   36.7   30.4   6.3  #  9.0
      20.0  24.0  12.06   3.63   36.4   30.6   5.8  # 10.0
      22.0  26.0  13.16   3.96   36.1   30.9   5.3  # 10.9
      24.0  28.0  14.27   4.29   35.9   31.0   4.9  # 11.8
      26.0  30.0  15.37   4.62   35.7   31.2   4.5  # 12.7
      28.0  32.0  16.48   4.95   35.6   31.3   4.2  # 13.6
      30.0  34.0  17.58   5.28   35.4   31.5   3.9  # 14.5

 

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Posted by rrinker on Friday, November 2, 2018 7:10 AM

 If the frog were curves at the same radius as the diverging rail in the curved turnout, then I might say that the frog 'angle' is the same as the diverging rate of the rails - but a curved frog wouldn;t have an 'angle' since it's curved, so assigning a number to it would not be in direct comparisoon to a straight turnout - possibly how model manufacturers get away with using rather arbitrary numbers. But if the frog is straight, a true angle between two lines, then it has a number that stays the same regardless of the radius imparted to any rails on the diverging side. Too shallow a frog angle (higher number) with diverging curves that are sharper than the substitution radius of an equivalent straight turnout, or the closure rail radius of an equivalent straight turnout, would be next to pointless, as who cares if the larger rigid wheelbase loco cna negotiate the frog if it can;t negotiate the tight diverging curve? Reverse I think would be true as well, why have a #4 frog feeding 60 and 32" radius curves, if the loco can get though the curves but not the frog? 

 If the frogs on commercial curved turnouts are curved - unless everyone agrees where to draw intersecting straight lines, any measurement of angle and thus frog number are somewhat subjective For there to be any consistency, each manufacturer would need to agree to measure from the same points within the turnout. I think that accounts for much of the variation in listed frog numbers. And if they can;t even agree to what the diverging rail radii are, and publish unrealistic numbers, good luck reconciling it all.

                             --Randy

 


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Posted by gregc on Friday, November 2, 2018 6:56 AM

riogrande5761
So ultimately is this all academic?

if I don't want to roll my own,

Not for me.  I'm trying to roll my own and am trying to reconcile the inconsistencies i read about with commercial turnouts.

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Posted by riogrande5761 on Friday, November 2, 2018 5:56 AM

So ultimately is this all academic? 

For curved turnouts, to me what really maters is how longer rolling stock is able to reliably operate through ether of the routes so I tend to focus on radius here.  Since many seem to report the inner radius is actually somewhat smaller than the manufacturer stated radius, if I don't want to roll my own, I try to use the largest available. 

I'm using a 32 inch minimum mainline radius for my layout so apparently the reported inner radius of some curved turnouts (such as the Walthers #8) is, depending on who you ask, something like 28 or 30 inches.  Some even believe the Peco #7 with it's stated 36" radius is closer to 30 inches also.

If the above is true, then the curved inner radius is smaller than the minimum I am trying to keep to, but my guess is if I use 32 minimum except for where the turnout is, that inner curve on the curved turnout is short enough to probably not have adverse affects on any rolling stock which might have issues below 32" curves.

AFAIK, I don't have any rolling stock that cant handle radius's significantly lower, like 28, even 26, but thats why it's helpful, if space allows, to use a minimum that has some built in margin for longer rolling stock over what is factory recommened.

I don't have any Walthers Empire Builder passneger cars, but recently I read a long forum discussion started by a modeler who was asking if his 9 car EB could run reliably on his 32 inch minimum curves.  Walthers apparently reports a minimum of 24" is recommended but hobbyists have found those EB passenger cars often don't actually work well on 24 inch curves.  In reality they really seem to need something like 28" radius or more, 32" being totally fine by a number of experiencial reports.

 

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Posted by gregc on Friday, November 2, 2018 3:58 AM

selector
A #6 frog diverges one unit toward the diverging route for every six units of length

let's make that unit 1/10"

see http://www.catskillarchive.com/rrextra/tkwk10.Html previously posted

do all all turnouts have to be the same

greg - Philadelphia & Reading / Reading

  • Member since
    February 2005
  • From: Vancouver Island, BC
  • 23,321 posts
Posted by selector on Thursday, November 1, 2018 9:19 PM

gregc

 

 
rrinker
you need to draw straight lines from the frog to determine the frog number.

 

do you?  Isn't the frog number ultimately the angle that the rails intersect at?

 

It may be on the prototype, in which case typical frog numbers would be puzzling to most modellers.  In our hobby, though, the frog number is simply the ratio of through axis progression over the divergence at the frog point and beyond.

A #6 frog diverges one unit toward the diverging route for every six units of length the rolling item moves parallel to the main axis...the through route.  Think of it as the ratio of 'through over run', and like the inverse of 'rise over run'.

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