Does anyone out there in trainland know the radius of a number 4, 6, 7 and 8 turnout ?
would greatly appreciate any and all info re radius of these turnouts (atlas or peco}
thanks
Rudy ceo Rockbottom Junction RR
You have asked a question that may lead to more education than you intended....
Numbered turnouts, strictly speaking, do not have a radius. The number defines the angle at which the diverging track leaves the straight track. This link :
http://www.ndrr.com/rmr_faq/Introduction/Definitions-and-terms.htm
has a table borrowed from John Armstrong's "Track Planning for Realistic Operations" in the third question down, which describes this and gives the 'substitution' radius for various turnouts, which is the radius which the turnout would be if it had a radius.....in other words if there was a continuous curve between the beginning and the end.
An exception to all of this is the Peco European style turnouts, which are curved though the frog, and do have a radius. That would not be so confusing, except that they now make North American style numbered turnouts as well, so you have to know which you are talking about to know what you've got.
Test on Thursday!
Jeff But it's a dry heat!
The NMRA RP 12.3 (http://www.nmra.com/standards/rp12_3.html for HO) the tightest radius contained within a "straight frog" turnout. It shows as line 11, the closure rail radius. Note that most manufacturered turnouts do not adhere to the NMRA RP very closely.
The Atlas #4 turnout, for instance, is really closer to a #4.5, and has a closure rail radius of about 22". I believe (have not measured to know for sure) the Shinohara #4 turnouts likewise have been lengthened to have a gentler closure rail radius than the table would indicate. Peco turnouts - except the HO code 83 line which does have straight frogs - have curved frogs with a constant radius through the turnout.
The question becomes - what problem are you trying to solve? Are you trying to match a turnout # with a curve radius? I assumed HO because of the Atlas #4 turnouts, but you don't say.
my thoughts, your choices
Fred W
Rudy, numbered turnouts have no radius, as the path through the frog is straight. Now Atlas HO Snap-Swithes have an effective radius of 18", because the diverging leg of the frog is curved. Peco Streamline turnouts also have effective radii for the same reason (though they list them as "short", "medium", and "long"). Also, you should know that the effective radius of a turnout depends on the track geometry of the entire turnout, which varies according to the manufacturer. The number refers only to the angle of divergence of the frog. For example, a number 4 turnout diverges one unit of measure in four units of distance - a number 5, one unit of divergence in 4 units of distance, and so on.
If you are thinking of putting a switch meant for straight track into the middle of a curve, you should be aware that it's not quite as simple as matching the effective curve radius of the switch. It's easier to put one in at the beginning. I found that the Peco Streamline medium-radius turnout, for instance, has an effective radius of about 38" for the diverging leg, and it fits right in with the outside track of my double-track mainline. Mosty manufacturers make curved turnouts, with both legs of the turnout curving in the same direction.
There's a mathematical formula for finding the radius of an arc of a curve based on the length and divergence of a chord on the curve, but it applies to circular curves, which a normal turnout definitely is NOT.
However, that said, I believe that Model Railroader, a number of years ago, published a list of the effective curve radii of the turnouts of various manufacturers. Perhaps a search of their archives would yield some results...
Good luck...
---
Gary M. Collins gmcrailgNOSPAM@gmail.com
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"Common Sense, Ain't!" -- G. M. Collins
http://fhn.site90.net
Last I knew, Bachmann's EZ-Track has fully curved diverging routes on their short turnouts, the ones that would fit well with 18" curves. I don't know if Atlas or Bachmann make non-ballasted turnouts of that configuration...maybe someone does?
I think Gary's reponse is quite useful. You will only ever get an approximation with any of the commercial turnouts, unless you go with the fully curved turnouts and use either the diverging or the "through" route to conform to your curve. Walthers/Shinohara makes them in several lengths and curvatures. I have both #7.5 and #8 curved turnouts by them. Note that I am not very happy with the performance of the frog on my #8. Many things wobble noticeably across it. FYI.
Jeff,
thanks I'am off to dig out John Armstrong's book - appreciate your quick reply.
Keep on tracking.
Rudy
Thanks, appreciate your quick reply
Hey Fred,
Thanks for your quick reply really appreciate it
Gary,
Thanks buddy, appreciate your quick reply
Thanks for your quick reply - really appreciate it - regards
MR had an article some months ago giving the critical dimensions of popular trunouts.
Mark
selector wrote: Last I knew, Bachmann's EZ-Track has fully curved diverging routes on their short turnouts, the ones that would fit well with 18" curves. I don't know if Atlas or Bachmann make non-ballasted turnouts of that configuration...maybe someone does?I think Gary's reponse is quite useful. You will only ever get an approximation with any of the commercial turnouts, unless you go with the fully curved turnouts and use either the diverging or the "through" route to conform to your curve. Walthers/Shinohara makes them in several lengths and curvatures. I have both #7.5 and #8 curved turnouts by them. Note that I am not very happy with the performance of the frog on my #8. Many things wobble noticeably across it. FYI.
I'm not familiar with this brand, but the frogs of #8s are long and the gap in the rail can be longer there, causing the wheels to drop down and then bump up. If your wheel flanges are of uniform depth, one can partially build up the frog so that the wheels don't drop.
Mark, thanks. One of my projects this winter will be to deal with this frog, now six months on the layout. I will see what the flange gauge on my NMRA gauge says about it, and I will try running only some twin axle trucks through it to see what's going on. I suspect you are absolutely right, and that I will have to glue in some nearly mm-thick plastic liners.
Just as a quick plug for the Fast Tracks system, but my handlaid turnouts work so much better because the frogs are correct. During the passage over the frog point and on to the closure rail, the frog guard rails catch the wheels before they can fall in the gap. Makes a huge difference.
-Crandell