Walthers states that their 20"/24" curved turnout has a #6.5 frog. I figure it to be a #10.5.
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?
Knowing the intercept of where the frog is located and the centers of the curves, I calculate the angle of the line between the curve center and intercept. The lines tangents to these are parallel to the corresponding frog rails. The difference between the angles is the frog angle from which the frog number can be calculated.
why are the frog numbers different?
greg - Philadelphia & Reading / Reading
Model track manufacturers seem to use their own terminology when labeling curved turnouts. If you are measuring the ratio of the distance to width, is that how you came up with 10.5 for your Walthers #6.5?
Using commercial turnouts, we pretty much have to make a "best-fit" for whatever are available on the market; either that or custom build your own using FastTracks.
Rio Grande. The Action Road - Focus 1977-1983
Look at your drawing. You show the whole turnout being more than 15 inches long. It is not. If you get your hands on the turnout, which I highly recommend, you'll find that it's the radius they lie about rather than the frog.
I have the right to remain silent. By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.
My guess is that in the case of curved turnouts, the term 'substitution radius' has more application and meaning because of the twin curved routes, something a conventional turnout won't offer the user. You can't practically insert a true NMRA-compliant #6 turnout into a 44" radius curve without a compromise at the turnout, a kink if you will, but that's not true for a curved turnout with the same frog number. At least, it 'should be' true for a curved turnout with the appropriate twin curved paths.
carl425If you get your hands on the turnout, which I highly recommend, you'll find that it's the radius they lie about rather than the frog.
if the commercial 20"/24" curved turnout is not really 20"/24" then any comparison is invalid.
selectorYou can't practically insert a true NMRA-compliant #6 turnout into a 44" radius curve without a compromise at the turnout, a kink if you will, but that's not true for a curved turnout with the same frog number.
I don't think that is correct for most (if not all) commercial curved turnouts. There is still a small amount of difference from a true curve radius owing to the points and frog. Much closer ̶t̶h̶a̶t̶ than a straight turnout -- but not exactly a circular curve.
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Byron, don't you have that ackwards? A curved turnout will be a much better fit into a curve than a standard NMRA type. The diverging route past the frog is straight for an inch or more. If one chooses to mangle the turnout and clip the rails almost immediately after the frog, then you could add curved rails from that point on. Personally, I'd just use a curved turnout.
cuyama selector You can't practically insert a true NMRA-compliant #6 turnout into a 44" radius curve without a compromise at the turnout, a kink if you will, but that's not true for a curved turnout with the same frog number. I don't think that is correct for most (if not all) commercial curved turnouts. There is still a small amount of difference from a true curve radius owing to the points and frog. Much closer that a straight turnout -- but not exactly a circular curve.
selector You can't practically insert a true NMRA-compliant #6 turnout into a 44" radius curve without a compromise at the turnout, a kink if you will, but that's not true for a curved turnout with the same frog number.
I don't think that is correct for most (if not all) commercial curved turnouts. There is still a small amount of difference from a true curve radius owing to the points and frog. Much closer that a straight turnout -- but not exactly a circular curve.
i think selector referring to closure radius
i don't believe this is suggesting that such a turnout can fit cleaning into a curve of the same radius
i do believe it is indicating what the tightest radius is for purpose of determining if a locomotive can handle the turnout. Locomotives have maximum track curvature limits
i'm planning on laying a curved turnout. I plan on making the frog match the inner/outer curve radii, which will be tight (hence the ? about frog #).
i see no need to "straighten" the rails around the frog (which I did with other turnouts i laid). I believe the guard rail should guide the truck, maybe widen the gauge a little.
selectorA curved turnout will be a much better fit into a curve than a standard NMRA type
That's exactly what I said -- or meant to say.
A curved turnout will fit better, but not perfectly, into a circular curve. I see that I accidentally typed "that" instead of "than", which may have created confusion.
gregc i see no need to "straighten" the rails around the frog (which I did with other turnouts i laid). I believe the guard rail should guide the truck, maybe widen the gauge a little.
Re: the prototype
I suspect the reason the rails are straight while running through the frog is that the designer/builder of that switch was using an off-the-shelf frog. Which is based on two intersecting straight lines.
A custom curved frog would likely cost much more than a standard one.
So, ya pays yer money and takes yer choice.
Ed
Likely true, remember the number for the frog is derived from the separation per unit distance for the FROG, not the whole turnout. Curve the rails past the frog to some radius and you may get a number completely different from the frog - you need to draw straight lines from the frog to determine the frog number.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
rrinkeryou 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 is directly related.
But it's more correctly (I think) the cotangent of the angle.
Is the frog number or angle of a frog in a curved turnout even relevant? I figured the minimum implied radius is the constraint. Implied radius of the diverging route is sort of the same issue with straight turnout but that's traditionally explained by the frog # when talking about straight turnouts.
- Douglas
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?
rrinker you need to draw straight lines from the frog to determine the frog number.
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'.
selectorA #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
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.
riogrande5761So ultimately is this all academic? if I don't want to roll my own,
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.
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.
rrinkera 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.
rrinkerToo 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.
rrinkerReverse 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?)
rrinkerif 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
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.
riogrande5761 So ultimately is this all academic? if I don't want to roll my own,
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.
DoughlessI 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.
Doughlessare 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
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?
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.
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.
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.
*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.
riogrande5761So 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.
7j43kBut 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).
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.
Dante
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.