# Meaning of RADIUS CURVE



## Bob Allen (Dec 14, 2018)

What does RADIUS CURVE mean. I see different lengths.


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## cv_acr (Oct 28, 2011)

Basic math terms describing the size of a circle:

"Radius" is the distance from the outside to the center of a circle or arc.
"Diameter" is the distance across from side to side of the circle. (or, twice the radius, obviously)
"Circumference" is the full distance around the circle if you were to complete a journey all the way around the outer edge.

With track we measure radius from the center of the circle to the center-line of the track.

'18" radius curve' then of course means a curve with a radius of 18 inches. This is what most standard sectional track contained in train sets is, although it's generally considered a fairly tight curve.


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## Bob Allen (Dec 14, 2018)

Thank you


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## ogaugenut (Dec 27, 2012)

Depends a little on what scale you are in. In O gauge, most curves are referred to by diameter such as O72, O36, etc, but many people refer to this as radius.


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## Bob Allen (Dec 14, 2018)

*HO*

RADIUS CURVE H.O. in inches


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## traction fan (Oct 5, 2014)

*Track radius*



Bob Allen said:


> RADIUS CURVE H.O. in inches


 Bob Allen;

When drawing a track plan, remember what cv acr said about the radius being measured from the center-line of the track. (If you are using Atlas snap track that would be the point where the nail holes in the ties are.)
A 180 degree, "U-turn," curve made up of 18" radius curved track sections will occupy about 38" of table width plus more space to accommodate the considerable overhang of cars and locomotives rolling through this tight a curve. An 18" radius turn-back (180 degree) curve will fit into the 4' width of a 4' x 8' sheet of plywood OK, but the 22" radius curves that are often used for an outer loop of track, will be crowding the edges of the 4x8 and, practically speaking, would be better off on a slightly wider table. In short, don't take the 18", 22", etc. radius designations as absolutes. Allow as much extra room beyond those dimensions as you can.

Traction Fan :smilie_daumenpos:


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## tjcruiser (Jan 10, 2010)

ogaugenut said:


> Depends a little on what scale you are in. In O gauge, most curves are referred to by diameter such as O72, O36, etc, but many people refer to this as radius.


True.

And in O, diameter is not necessarily measured to the center of the track between the rails. It's confusing. O27 is 27" diameter to the outside rail of the circle; however, O72 is 72" to the center rail (of 3 rails) of the circle.


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## tr1 (Mar 9, 2013)

*6axcel on a small radius curves(18")*

Is it possible to successfully modify a 6axcel athern U-boat diesel truck, in order to negotiate a 18" radius curves ?
Regards,tr1


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## mesenteria (Oct 29, 2015)

Yes. Grind down the flanges on the middle axles of both trucks...that may work. Or, simply replace those axles with 'blind' wheelsets if you can find them. Blind being the rails' term for flangeless wheels.

But, that may only solve one problem and leave another. That would be coupling. With the ends of the 'boat' sticking out over the outside rail on such sharp curves, your couplers would probably want to drag the rolling stock to which they are coupled out and over the rails...and that's IF they stay coupled at all.


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## rickbz28 (Jan 10, 2016)

tr1 said:


> Is it possible to successfully modify a 6axcel athern U-boat diesel truck, in order to negotiate a 18" radius curves ?
> Regards,tr1


Your question got me thinking and led to a little experimentation.
The following Athearn diesels pulling a 12 car train with a Genesis 57' reefer coupled to the engine all ran through a 18" radius curve and a number 4 turnout without any issues what so ever. No derailing of the loco or any of the cars. The test was run both in forward and reverse.
U28C blue box
AC4400 blue box and RTR
SD40-2 blue box and RTR
SD50 RTR
SD70I Genesis
DD40 blue box
Also the following KATO without issue
SD40-2
SD80MAC
I will say that some of them don't look very good on that radius curve but all successfully traveled through without problems.
Hope that helps.


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## Bull6791 (Dec 14, 2015)

Lionel fastrack/Radius curve question: my platform is a 4x8 sheet of plywood. I am using Lionel fastrack. I have one oval/circle on my plywood. The oval has 36”curves. 
My question is if I wanted to make a second oval/circle what curves would I need. Should I use 48” curves on outer oval and 36” curves on inner oval. Should I use 36” curves on outer oval and 31” curves on inner oval. I want to get 2 or 3 ovals on my platform. I just don’t know what curves I would need. 
I already have one oval with 36” curves on my 4x8 platform. Thanks for the help.


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## Tom_C (Jan 8, 2016)

Bull6791 said:


> Lionel fastrack/Radius curve question: my platform is a 4x8 sheet of plywood. I am using Lionel fastrack. I have one oval/circle on my plywood. The oval has 36”curves.
> My question is if I wanted to make a second oval/circle what curves would I need. Should I use 48” curves on outer oval and 36” curves on inner oval. Should I use 36” curves on outer oval and 31” curves on inner oval. I want to get 2 or 3 ovals on my platform. I just don’t know what curves I would need.
> I already have one oval with 36” curves on my 4x8 platform. Thanks for the help.


Radius is the distance between the center of a circle to the edge of the circle. I think most track is measure to the centerline of the track, so a 36 inch circle will be to the center of the track.

As has been suggested, download anyrail or scarm and you can use the track libraries built into the software to layout your track on the size of your platform, and it will show you exactly what you can do.

I posted a picture of anyrail that I laid out for you showing what you could do. Someone else also linked you to a track plan showing 2 ovals on a 4.5'x8 board.


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