these are the recomendations - NMRA RP-12.3
my guess is not all manufacturers. I guess one blatant exception is the atlas snap-turnout.
but i'm wondering why? did the manufacturers finds that things worked better with a different geometry, or maybe that RP simply didn't match prototype turnout dimensions
i've studied them over the years and spent some more time today. In particular, I looked at what radius curve would fit between the points and match the frog angle AND what is the lead length (distance from points to frog). In some cases, i found an awkward fit, even when you consider that the switch points my be at a larger radius than the curve nearer the frog. I found that a shorter lead would work for a #4, but all others required a larger lead.
for the RP values, I also found relatively proportional changes in dimensions between frog numbers 4-6 and 7-10, but an abrupt difference between from number 6 and 7.
I could go into more detail but was hoping someone already went through this and had some understanding. I found some comments made by Andy Sperandeo suggesting better looking turnouts could be made following prototype dimensions
greg - Philadelphia & Reading / Reading
The answer is no.
Sometimes like the Snap-Switch there is no matching standard. The Snap-Switch has an 18" curve through the diverging leg. This matches up with the 18" radius curves. But curved leg switches are not covered by the RP.
Other times the manufacturer just didn't follow the RP. Unlike standards, they will still work although there may be some limitations or in the case of Atlas #4's they are really 4 1/2 to have a larger radius in the closure rail.
Enjoy
Paul
Blatant exceptions aside, I think you'd find that very few turnouts actually meet all the RP requirements. Yet trains operate pretty well over most. Andy's right, a turnout that is constructed to scaled dimensions would look better. There's some question as to whether it would work better. The way mass scales differently than linear dimensions accounts for part of this, but also the fact that a turnout doesn't need to be scale to work properly, fortunately enough.
Mike Lehman
Urbana, IL
In my experience, there is only one way to assure that a specific model turnout meets specifications - NMRA, AREA, ASCE or whatever entity sets the standards for the prototype you follow. Build it yourself.
Manufacturers are sometimes forced to compromise by the constraints of their machinery. Model turnouts are non-standard precision assemblies - not the easiest things to put together economically with relatively inexpensive equipment. (The volume and value preclude high precision automation.) You, armed with file, pliers, gauges and soldering tool, can take the time to do it right. There are no 'seconds' among hand-laid turnouts, since they can be (and are) reworked as necessary to achieve near-perfection.
And then there's the bartender at the abolitionist convention. What if your modeling absolutely, positively has to include a turnout on a superelevated curve? Or three way switches with all routes curved left?
The fact that the price is right (CHEEP!!!) is just gravy.
Chuck (Modeling Central Japan in September, 1964 - on hand-laid specialwork.
so if few manufacturers meet the RP and those who handlay turnouts, such as myself, lay to fit, what value is the RP?
Are there standard turnout designs for the full scale railroads?
gregc so if few manufacturers meet the RP and those who handlay turnouts, such as myself, lay to fit, what value is the RP?
"getting everything mostly right so things don't fail spectacularly every single time you try to traverse this bit of track"?
Thing is, the RP isn't meant to cover situations of "Lap turnout with all three routes swinging left", but more "this is about as small/tight as you can make this piece of trackwork". At least that's how I'm reading it anyway...
gregcAre there standard turnout designs for the full scale railroads?
Yep.
-Dan
Builder of Bowser steam! Railimages Site
I believe that only the Fast Tracks jigs are built to the NMRA RP -- which is actually somewhat unfortunate, in my humble opinion, because they could have been built with a longer lead for better appearance.The RPs are one set of dimensions that “work”, which is why they were published. But individual manufacturers, likely for their own idiosyncratic reasons, chose other sets of dimensions along the way.
Layout Design GalleryLayout Design Special Interest Group
gregcso if few manufacturers meet the RP and those who handlay turnouts, such as myself, lay to fit, what value is the RP?
Think about things if we didn't have a unit of measurement. You could say something's a yard long, but no one but you would know what you meant. With a yardstick, you may not need the precision of even getting it out to measure with, but you do roughly know how long that is and so does everyone else. With the RP, you have a "yardstick" for what will work, roughly. It's roughly the "middle of the road."
Yes, manufacturers do vary. Most I suspect due to manufacturing practices and tolerances more than anything. But there are those who conciously push the envelope of the RPs for a purpose. At least one custom turnout builder uses a rather tight flangeway to avoid wheels dropping as they go through the frog.
An example of where this is an issue are the Shinohara dual gauge turnouts, the only such RTR commerically available turnout in HOn3. Run a string of cars through the narrowgauge side and watch the cars shudder as the wheels hit the primary frog. I don't need to know all the particulars to know that something isn't quite right there, even though cars do just fine getting across -- other than doing the bump thing. My dual gauge install was all in place with Shinoharas before I realized there was both a problem and a solution for it. It was cheaper and easier to just go back to ignoring things my ignorance previously shielded me from...
i tried fitting a curve between the points and the frog. I figured there is a curve of constant radius that extends from the points and ends at the same angle as the frog angle. What I also realized is that this also dictates the lead length, the distance from the points to the frog.
In some cases, I could not fit a curve within the lead specified by RP-12.3. I realize that the curve may not be constant. And if this is the case, i believe the lead length would need to be even longer.
i found some prototype turnout dimensions to compare to
i get the following values when I use 4'8.5" (4.708") as the gauge (which are close to those above)
frog angle radius lead 12 4.8 1350.9 112.69 11.5 5.0 1240.8 107.99 11 5.2 1135.3 103.29 10.5 5.4 1034.6 98.59 10 5.7 938.6 93.89 9.5 6.0 847.3 89.20 9 6.3 760.7 84.50 8.5 6.7 678.8 79.81 8 7.1 601.6 75.12 7.5 7.6 529.1 70.43 7 8.1 461.3 65.74 6.5 8.7 398.3 61.06 6 9.5 339.9 56.38 5.5 10.3 286.2 51.70 5 11.3 237.3 47.04 4.5 12.5 193.0 42.38 4 14.0 153.5 37.73these are the values I come up with for HO frog angle radius lead 4 14.0 17.9 4.85 4.5 12.5 23.1 5.50 5 11.3 28.9 6.16 6 9.5 42.4 7.47 7 8.1 58.6 8.79 8 7.1 77.4 10.11 9 6.3 98.9 11.42 10 5.7 123.0 12.74the leads for frog number 5 and up are longer as well as the radii (except for #6)