Can anyone tell me the radius for # 4,#6 and #8 switches in HO.I want to run #8’s on my mainline and #4’s on my shortline.Need to know if I’m accurate in my trackplan design.Enough room is always an issue.
Thanks
Terry
Terry,
There is no real radius for ‘numbered’ switches. Protoype switches are constructed with a straight divirging route. For example, a ‘#4’ turnout will divirge from the mainline 1 unit to the side for every 4 units forward. This results in about a 14 degree angle. A #6 is more gentle and a #8 moves away at an even more gentle angle. There really is no ‘replacement’ radius that you can use to ‘drop’ them into a curve. The NMRA has a table with approximate replacement radius info, but not all manufacturer’s have the same dimensions. here is the table:
http://www.nmra.org/standards/rp12_3.html
The closure radius for a #4 is about 15". for a #6 it is about 43", amd for a #8 it is about 67". These numbers are approximate and vary with each manufacturer. The Atlas ‘Snap Switches’ do have a constant radius(18") through the switch and can be placed in an 18" radius curve.
Jim Bernier
#4s are awfully tight, even for branchlines. NMRA also has recommendations for turnout size and track radii for various types of locomotives rolling stock which you should consult… I suggest you use #5s instead if at all possible.
Mark
If your using the Atlas #4 snap switches then I believe that they are 18" radius, I’m not sure about the #6 or 8 .
bill
Atlas #4’s are actually 4 1/2’s.
The NMRA table has two radii, the larger switch radius and the smaller closure rail radius. The switch radius is large enough to not be a problem, but the closure rail radius affects how the fixed length wheel base parts of the rolling stock does. This is mainly an issue for steam locomotives with their longer wheel bases.
Number 8’s on the mainline will handle everything. #5’s (or Atlas #4’s) are probably a better choice for the shortline, although regular #4’s can work as long as you limit your equipment.
NMRA RP 11 http://www.nmra.org/standards/rp-11.html can provide guidance.
Enjoy
Paul
Atlas “snap switches” use an actual curve through the frog and thus have a real radius (sort of like Lionel switches which simply meld a straight with a curve so that they are interchangable in track plans). In that sense they differ from true Atlas #4s.
I think Peco’s catalog shows the equivalent radius for their turnouts especially the curved turnouts. I seem to recall that the large curved turnout is said to be a 30 inch radius and a 60 inch radius. Whether this is exact or Peco’s best approximation is not clear, but I think they also show radius for their regular turnouts as well as they Ys
Dave Nelson
Please let me throw in my own questions. What do you think is the smallest turnout # to be used on prototype mainlines? I am modelling the late steam era with these monster engines, have a large room and therefore don’t want to accept any compromise in curve radii.
Same question on normal curves: what do you think would be the smallest H0scale radius to be prototypical?
Thanks and Regards
VAPEURCHAPELON
Someone will correct me if I am wrong, as this is kind of from memory, but I think the smallest switch you’ll find (low speed, etc.) in the prototype world (not including trolleys and the like) is probably near a #10. As far as curve radius, I believe that Horseshoe Curve (pretty sharp), is around 9 degrees, which translates to nearly 90 inches in HO.
before you get started …
CURVETURE imposes restictions on tracking.
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LOWER Numbered (#) turnouts need shorter wheelbases and slower speeds to navigate. HIGHER numbered tornouts allow longer wheelbases and higher speeds.
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SIZE of your LAYOUT determines maximum curveture. A 4X8 limits us to 22"r. maximum curves.
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SIZE of your ROOM determines SIZE of your layout, or design.
THAT being said, #4s are used for yards, #6s for most mainlines, #8s are higher-speed #6s, and 90% of today’s equipment will run on 22" radius.
ATLAS ‘snap’ switches are for beginners and form a 36"d. circle (18" r.) which limits what will run properly to 4 axle locos and 40’-60’ cars.
ARE there exceptions? Sure, but they’re exceptions.
Thanks…Great info and reference.I appreciate it.
My mainline will be a 44 inch radius outside track and 41 1/2 inside track exposed.Shortline will be 18 inch radius.
Terry
If by not accepting “any” compromises in curve radii you mean you will settle for nothing less than full size prototype high speed turnouts and curves you are looking at quite an undertaking. A number 10 switch, which is huge in HO, would be a slow speed switch on the real thing. A normal speed number 20 switch in HO would be – what? – maybe longer than a yardstick? My layout has 40" curves but I am under the impression that I would have to quadruple that number to even approach what the C&NW had in South Milwaukee WI which is what I am modeling. I did not want to compromise excessively but I am accepting reasonable compromise, since after all the wheels and flanges and mechanics of my cars and locomotives have a high degree of compromise built in. And the fact that my basement has walls forces a certain degree of compromise as well.
Dave Nelson
i’ve designed & surveyed some prototype turnouts and a #7 is just a little tight for mainline power at 15 or 16 degree closure rail curvature (from tangent). on the other hand, NP had some #5’s on industrial trackage, and the tacoma municipal bert line had #4’s on its shop lead, used by alco S-2’s. my hero, william c. van horne, before he went north to the canadian pacific in 1881, was gen. mgr of the milwaukee road, and when a draftsman told him a #7 was too sharp for road power, asked what the frog number worked out to for a 14 degree closure rail, and found it was #7 - 1/7. i’ve surveyed in quite a few for new construction in the 1960’s-70’s! the HO equivalent would be atlas’s #4 - 1/2 which they sell as a #4; it has a curve radius of about 22" compared to about 16" for a true #4. and if it’s a wye, you can use a frog number 70% of the equivalent from tangent; i.e., #5 wye equals a #7 straight, a #7 wye equals a #10, etc. -big duke
Bigduke,
I am a little confused by your measurements. A #6 turnout is a 9.5 degree angle of divirging. The Atlas ‘#4’ which as you mentioned is really a #4.5 and divirges at a 12.5 degree angle. A 14 degree angle works out to about a #4 turnout. Wye or ‘Equallateral’ turnouts are simply 1/2 of the frog number for the divirgence. A #5 Wye divirges like a #10 to each side. Now, the total length of the turnout may be only about 70 percent of a normal #10…
Jim