# Radius, Diameter or Degrees?



## Tom Bowdler (Jan 3, 2008)

At a recent steamup a semi-lively discussion debated the need for a "standard" when talking about the curvature of our model track. Some folks favored always using DIAMETER as the standard, others espoused RADIUS since most of the time we are using segments less than half of a circle, and one wag (a professional railroader) suggested we could use DEGREES like the full size guys do. 

I think establishing a guideline when talking about curves would be useful so that when a post appears like Tomh's recent query about track spacing and mention is made of "10 ft curves" we would immediately know what he is talking about. 
What do you all think? 
Tom


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## Marauderer (Jan 5, 2008)

*RE: Raius, Diameter or Degrees?*

If a person wants to be a miniature Railroader they would use degrees If they are a garden railroader they will use whatever is convenient that they understand. I think most people understand radius and diameter but not degrees. That doesn't mean they can't learn. /DesktopModules/NTForums/themes/mls/emoticons/w00t.gif It makes an interesting discussion but, I think most garden railroaders do not give a hoot one way or another./DesktopModules/NTForums/themes/mls/emoticons/wow.gif JMNSHO!!


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## DKRickman (Mar 25, 2008)

*RE: Raius, Diameter or Degrees?*

For what it's worth, every other (smaller) scale that I'm familiar with uses the radius as the standard measurement. 

If you think about it, drawing a curve using a compass requires knowing the radius, so that's the most practical known dimension in a smaller scale. I don't know how most people lay track, or plot their track locations on the ground, but I would think that it would still be more useful to define the radius in G scale. 

I definitely agree that there ought to be a single standard way of discussing things.


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## Marauderer (Jan 5, 2008)

*RE: Raius, Diameter or Degrees?*

Posted By DKRickman on 09/01/2008 6:36 AM
I definitely agree that there ought to be a single standard way of discussing things.




I would have to agree with you on this.


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## ralphbrades (Jan 3, 2008)

*RE: Raius, Diameter or Degrees?*

Well I agree -lets use the largest most commonly used method of determining the curvature of track. 

So let us all use *CHAINS*. 

This measurement is still used on British Rails, former Empire & Colonies, and most of South America. 

My 16mm models are all designed to take a (scale) 0.75 chain curves and my Gauge 3 models to take 
a (scale) 3.5 chain curves. Typical "real world" values would be 3 chains and 8 chains repectively. 

Calculation of Super Elevation of curves is thus quite easy: SPEED (mph) divided by CHAINS = SE in 16ths of an inch. 

regards 

ralph


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## Idraw4u (Aug 19, 2008)

*RE: Raius, Diameter or Degrees?*

As a complete newbie to the hobby... you guys are mostly taking over my head… but if my two cents matter, it would seem to me it would be best to use whatever method the track manufactures use “diameter”. After all that is how I have to order curved track isn't it? 

Diameter, radius, degrees and even links(?) would work for those that understand them but the track manufacturers are still going to sell track the way they do and that is where we are all going to first be exposed to curved track terminology. 
In all fairness, for those of us just getting into this we're going to be asking the same dumb questions over and over and confuse radius and diameter (I apologize ahead of time)... For those of you already up to your necks in large scale and have been doing this, your going to use whatever terminology you have been using and are comfortable with. 

So I say whatever is on the side of the box would make it easiest for those of us getting started and it is comprehendible by everyone… even if it is not the most correct for ever situation (flex track, belly bending, etc…). 

But that is just my opinion and we all know what they say about those…/DesktopModules/NTForums/themes/mls/emoticons/whistling.gif. 

Best wishes. 

Todd


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## DKRickman (Mar 25, 2008)

*RE: Raius, Diameter or Degrees?*

Posted By Idraw4u on 09/04/2008 2:41 PM
So I say whatever is on the side of the box would make it easiest for those of us getting started and it is comprehendible by everyone… even if it is not the most correct for ever situation (flex track, belly bending, etc…). 

Best wishes. 
Todd 


Todd, 

That is exactly the point of this thread. Different manufacturers, and for that matter different scales, put different things on the side of the box. Whether it's diameter, radius, chains, degrees, or any of a number of other obscure measurements really doesn't matter as much as that we all - including the manufacturers - can agree to use the same thing all the time. What exactly are R1, R2, and R3, and are they the same for every manufacturer? I've heard not, which is an insane situation. 

For what it's worth, anyone with a basic understanding of geometry shouldn't have a problem with either radius or diameter, but it's been a long time since some of us were in school. 

Chains and degrees have the advantage of scaling easily, but they're not very practical when trying to draft a layout. 

I once again suggest that raduis is the most useful measurement, especially for those of us who are moving up from the smaller scales (and I suspect that number is pretty significant). Since it's used as the standard for the smaller scales, people with any familariaty with them will be in familiar territory. For anyone coming into the hobby completely new, one measurement is as good as any other, so why not one that will at least help a significant portion of the hobby?


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## Idraw4u (Aug 19, 2008)

*RE: Raius, Diameter or Degrees?*

Posted By DKRickman on 09/04/2008 3:08 PM
Posted By Idraw4u on 09/04/2008 2:41 PM 
So I say whatever is on the side of the box would make it easiest for those of us getting started and it is comprehendible by everyone… even if it is not the most correct for ever situation (flex track, belly bending, etc…). 
Best wishes. 
Todd 


Todd, 
That is exactly the point of this thread. Different manufacturers, and for that matter different scales, put different things on the side of the box. Whether it's diameter, radius, chains, degrees, or any of a number of other obscure measurements really doesn't matter as much as that we all - including the manufacturers - can agree to use the same thing all the time. What exactly are R1, R2, and R3, and are they the same for every manufacturer? I've heard not, which is an insane situation. 
For what it's worth, anyone with a basic understanding of geometry shouldn't have a problem with either radius or diameter, but it's been a long time since some of us were in school. 
Chains and degrees have the advantage of scaling easily, but they're not very practical when trying to draft a layout. 
I once again suggest that raduis is the most useful measurement, especially for those of us who are moving up from the smaller scales (and I suspect that number is pretty significant). Since it's used as the standard for the smaller scales, people with any familariaty with them will be in familiar territory. For anyone coming into the hobby completely new, one measurement is as good as any other, so why not one that will at least help a significant portion of the hobby?




Kenneth I see your point. 
Humm… That just adds to the confusion for a newbie. 
I think it safe to say that anyone that knows what a diameter is should know that a radius is ½ that dimension. 
So going with that logic… If you standardize the terminology amongst users on this site to mean a curve of any size is measured in “Radius” that would work for any scenario. 

Being new to this hobby and to this site, it seems to me that more people/manufactures refer to diameter when talking about curves then radius. But radius would seem to have more use and be more appropriate in more cases. 

Your quest continues…. 
I am happy to refer to them in whatever manner you guys want. 

Todd


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## BigDigger (Jan 3, 2008)

*RE: Raius, Diameter or Degrees?*

First keep in mind that many of us use "flex" type track or hand lay our own. We need a way to measure our curves for consistancy when building them. 

Indeed degrees is what is used in prototypical construction of railroads, highways etc. Generally, using radius is the easiest way to lay out a curve as long as there are no obstacles, however in heavy timber or mountainous areas for example and the methods for surveying used for years before GPS technology, radius would be inefficient, therefore degrees is used for curves in 1:1. 

In model railroading radius is the easiest and most accurate way to lay out curves. Laying one out in degrees (in our chosen scale) would be cumbersome at best. Could be done but I don't know why. In other words trying to lay out a curve in scale as a surveyor would do in 1:1 would be alot of work compared to laying out one using radius. 

Diameter is of course twice the distance of the radius of a given curve. This is where the confusion usually occurs, the difference between diameter and radius. So if it's a 10 ft diameter curve that curve has a 5 ft radius. Diameter is the total distance across a curve or circle. 

IMHO each one of these measurements are indispensable in our hobby. Using prototypical curve measurements in degrees and then converting that to radius or diameter in scale of your choice if you wish. Or knowing that your 5 foot radius or 10 foot diameter curve in 1:20.3 is actually 59 degrees in 1:1. 

The following link is one Rick Blanchard has on his site for degree and radius conversions. 

http://www.urbaneagle.com/data/deg-curve.txt 

David


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## Guest (Sep 6, 2008)

flex track, belly bending, etc…


don't start to standardize belly curvatures, please!


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## Torby (Jan 2, 2008)

Is that an R1 or an R8 belly


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## Guest (Sep 6, 2008)

that is no "R"belly. it is more of a diameter-belly


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## John Gates (Jan 4, 2008)

Seems like a no brainier here. Over 90% of the model railroading family has used RADIUS scene before I started.


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## John J (Dec 29, 2007)

I thought that when you "HAND LAIED/SPIKED" your own track you made curves as needed. There fore Curvature such as Diamater, Radius,or degrees did not count. Have I made the wrong conclution? 

I vote for 10 ft 20 ft Diamater ECT


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## DKRickman (Mar 25, 2008)

Posted By John J on 09/08/2008 5:44 AM
I thought that when you "HAND LAIED/SPIKED" your own track you made curves as needed. There fore Curvature such as Diamater, Radius,or degrees did not count. Have I made the wrong conclution? 
I vote for 10 ft 20 ft Diamater ECT 

You may lay the curve to suit your needs, but there's still a minimum curvature that you need to be aware of. How you define such things for yourself is your own business, but if you wish to discuss it with anyone else, a standard terminology is useful. 

We wouldn't get very far as a society if every one of us measured speed, distance, temperature, time, money, etc. differently.


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## davidarf (Jan 2, 2008)

Kenneth 

I agree, a standard is very helpful - so long as the standard is meaningful. I always use radius when working up drawings in CAD or laying out track in the garden, but I am also comfortable with diameter. What I cannot see any sense in is meaningless numerical references that require a conversion table to get them back into the real world sizes. So please can we see an end to the use of R1, R2, R3. I put these in the same time wasting rubbish bin as SWG and numerical drill sizes. 

Sorry for the winge folks, but it is a pet hate of mine.


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## jimtyp (Jan 2, 2008)

For someone fairly new to the hobby I prefer Diameter because that way I know how far apart the rails will be on a curve. If the track is 10' diameter, then I know I need to allow for a 10' space. If the track is given in Radius, for example 5' radius, then I can double it and then know I need to allow for a 10' space, so not so bad. For degrees or chains the math gets more difficult for me. 

I also do not like the R ratings as I can never remember what they stand for. 

I realize that for fine modelers that something like degrees or chains would be more exact to replicate a particular location, but if you are that advanced at modeling I think it is easier to do the math and with flex track and rail benders you can get exactly the degrees and chains you'd like. 

P.S. BigDigger, thanks for the link to the conversion chart.


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## Oldman (Sep 20, 2008)

To me it doesn't really matter how someone figures there curves but for myself, I always figure curves in radius. It is verry simple to draw, lay out and figure. The thing that folks DO need to do though is, whenever they are writing in these forums, specify what unit of measure they are using, be it radius, diameter, MM, chains or whatever. That way we aren't guessing. I find it somewhat annoying when they reference a 10' circle and always wonder if they mean radius or diameter.


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