Newbie Question: What are the actual radii of the various curves?

[T140V]

Returning to the hobby after a break of just over half a century and blimey, things have moved on a bit haven't they? I'm currently designing my layout and TBF I'm a bit confused as to how curve radii are actually measured. Take 3rd Radius curves as an example.

 

A standard piece of Peco Settrack 3rd radius is described as being 505mm / 19.75", but a 3rd Radius Tracksetta template is listed as having a radius of 21".

 

Does this mean that the two curve radii are actually different, or is it just a question of what is actually being measured? I had assumed that it would be correct to measure the radius at the centre line of the track. My worry is that I was hoping to use set track sections in some places and then use flex track in others, but if the radii are actually different it's going to complicate my track planning somewhat.

 

Many thanks for any and all enlightenment.

[RobinofLoxley]

While I don't know the answer to the original question, thinking it's to do with the reference point of measurement, mixing setrack and Flexi is commonplace. It's more a question of keeping gauge of track separation especially with streamline or similar turnouts. Generally you would use Flexi for 'free form' curves, not using Flexi to duplicate a setrack curve which in any case is not a good idea for reasons I won't go into here for sale of brevity. If you thought about creating a section of a setrack curve from Flexi do that by cutting a bit of setrack. 

 

If you have a play with Anyrail or a similar planning software - There is a free version to try - you will see how easy mixing track types is.

[Dungrange]

@T140V - Welcome to RMWeb

 

The quoted radii is the centreline radius.  Tracksetta templates are not available for the Set Track geometry.  If you want curves to the Set Track geometry, then these are available pre-curved and ready to lay without the need for buying Tracksetta templates.  Tracksetta templates are intended to be used with flexible track so that you can lay smooth larger radii arrangements and these go up in increments of 3" or 6", which differs from Set Track track centres (67mm).  You can use both in a layout if you want.  It's quite common for people to use flexible track with gentler flowing curves in the 'scenic area' and then use Set Track curves at the ends of layouts to fit their plans into the space available.  Just try to avoid first radius if you plan to use newer or larger locomotives and stock, since most aren't designed to go round first radius curves.

[Harlequin]

Here's Peco's Set Track geometry:

 

One other thing about mixing set track and flexi to watch out for is that Set Track always uses Code 100 rails whereas flexi track is available in either Code 100 or Code 75. You can get adapters to join Code 100 to Code 75.

 

Edited May 22, 2023 by Harlequin

[RobinofLoxley]

4 hours ago, Harlequin said:

Here's Peco's Set Track geometry:

 

One other thing about mixing set track and flexi to watch out for is that Set Track always uses Code 100 rails whereas flexi track is available in either Code 100 or Code 75. You can get adapters to join Code 100 to Code 75.

 

Actually that has Hornby code numbers but the dimensions are the same

[spamcan61]

Personally I find Anyrail very useful for 'sketching out' a trackplan as it does all the measuring for you.

 

https://www.anyrail.com/en

[T140V]

Thanks all. I had naively assumed that a 2nd or 3rd radius curve would have a standard dimension, but now that I know I can plan accordingly. As a Mac user, I'm using Rail Modeller Pro for track design which is ok but has some glaring issues when it comes to design (like you can't define a Tracksetta 21" radius curve for example) - so much so that I've started using Inkscape for some aspects of the design.

 

Because of the physical constraints of the location I'm going for Set Track in a couple of places and will be down to 2nd radius for a couple of turns. Not too worried as I'm modelling a rural branch line so no big stuff.

[5BarVT]

14 hours ago, T140V said:

As a Mac user, I'm using Rail Modeller Pro for track design which is ok but has some glaring issues when it comes to design (like you can't define a Tracksetta 21" radius curve for example) - so much so that I've started using Inkscape for some aspects of the design.

I use XtrackCad for layout design - it’s available in a macOSX version.  Has a bit of a learning curve, but not as much as Inkscape!

it has setrack pieces defined and flex can take any radius you want to specify.
Paul. 

[Harlequin]

14 hours ago, T140V said:

I had naively assumed that a 2nd or 3rd radius curve would have a standard dimension

 They do. See technical drawing above.

 

[spamcan61]

1 hour ago, Harlequin said:

 They do. See technical drawing above.

 

..but not between Setrack and Tracksetta, it seems (news to me)

[Harlequin]

1 hour ago, spamcan61 said:

..but not between Setrack and Tracksetta, it seems (news to me)

 

I see what you mean but anyone who uses the term "2nd Radius" (for instance) in terms of trackwork or minimum radii for rolling stock is always referring to the Set Track geometry.

 

Tracksetta appropriating the same terms for different radii is confusing but the most widely understood Set Track meaning is still the "standard dimension".

 

[Flying Pig]

24 minutes ago, Harlequin said:

Tracksetta appropriating the same terms for different radii is confusing but the most widely understood Set Track meaning is still the "standard dimension".

 

 

I'm not sure who makes Tracksetta now, but it is listed on Peco's website by radius only.  There do appear to be some retailers claiming for example that 21 inches is "commonly known as 3rd radius", but this is incorrect and misleading and they really should know better.

[T140V]

On 24/05/2023 at 12:13, Flying Pig said:

 

 

I'm not sure who makes Tracksetta now, but it is listed on Peco's website by radius only.  There do appear to be some retailers claiming for example that 21 inches is "commonly known as 3rd radius", but this is incorrect and misleading and they really should know better.

And it is exactly this that led to my confusion. I had seen the Tracksetta 18" listed as 2nd Radius, 21" as 3rd radius, and so on. 

But now I know they are actually different, it was matter of minutes to draw up the necessary templates to use in Inkscape to do the track plan. 

[davknigh]

I have to wonder why the terminology of first, second and third radius was used instead of simply stating the radius of the curve. Why introduce arcane terminology when a simple figure will be much more clear, especially to the novice?

 

Cheers,

 

David

 

 

[Derekl]

On 24/05/2023 at 12:13, Flying Pig said:

I'm not sure who makes Tracksetta now, but it is listed on Peco's website by radius only.

Peco makes it now - I have only seen it described as the curve radius.

[PeterStiles]

10 minutes ago, davknigh said:

Why introduce arcane terminology when a simple figure will be much more clear, especially to the novice

 

You're talking about an industry that freely mixes metric and imperial measurements on a daily basis?

 

I think 1st, 2nd and 3rd radius are far easier to manage than "xx millimetres" (or "yy inches").

 

I think we should feel lucky that the major manufacturers in the UK use the same terminology for curve-radii - look at the 'n' gauge situation in Japan where the two main manufacturers of track offer incompatible options... Or at "G" scale where the main culprits offer slightly different geometries..

 

(4mm to 1 foot is not exactly sane is it?)

 

 

[PeterStiles]

maybe I should think of a different word than sane....

[Dungrange]

On 26/05/2023 at 14:49, davknigh said:

I have to wonder why the terminology of first, second and third radius was used instead of simply stating the radius of the curve.

 

I have to say I've never seen Tracksetta templates sold as anything other than the radius in inches, and has been highlighted, Peco don't claim that they match the set track geometry and I don't think ever have.   I suspect that it's simply some retailer or E-bay seller that has thought it would be "helpful" to highlight that an 18" Tracksetta (radius 457 mm) is similar to a second radius set track curve (radius 438mm) and a 21" Tracksetta (radius 525 mm) is similar to third radius set track (radius 505 mm).  That might be helpful if properly explained, but not when we live in a 'sound bite' world where equivalence is then implied.  Others may have copied from whoever had the 'idea'.

 

As for the terminology in relation to set track, I think 1st, 2nd, 3rd and 4th makes perfect sense.  Hornby et al are selling this track into a child's market place and it is easier for children to know that there are four different radii known as 1st, 2nd, 3rd, and 4th rather than track with radii of 371 mm, 438 mm,  505 mm and 572 mm.  It's also easier for adults - I was able to write 1, 2, 3 and 4 with ease, but I had to look up the radius of each before posting.

Edited May 30, 2023 by Dungrange
wrong write!

[davknigh]

I suppose my reaction is partly due to outside influences from my own side of the pond where all set track is done in inches.  

 

 https://shop.atlasrr.com/c-486-h43.aspx

 

Up in the snowy north where I live we don’t have anyone who manufactures RTP track so our education in the mysteries of metric is wasted when it comes to making purchases.

 

As far as “sane” goes, I model in P4 so I’m hardly qualified to judge others…

 

Cheers,

 

David

[DCB]

On 26/05/2023 at 19:49, davknigh said:

I suppose my reaction is partly due to outside influences from my own side of the pond where all set track is done in inches.  

 

 https://shop.atlasrr.com/c-486-h43.aspx

 

Up in the snowy north where I live we don’t have anyone who manufactures RTP track so our education in the mysteries of metric is wasted when it comes to making purchases.

 

As far as “sane” goes, I model in P4 so I’m hardly qualified to judge others…

 

Cheers,

 

David

Best to use British Metric, 1000 mil equals a Meter. 1000 Meters equals a Klometer (Clom - Eater) or Click Also 300 mil equals a foot.  Otherwise you get your Dessis and Dekkas mixed up and that makes a real porridge of your calculations.

Edited June 9, 2023 by DCB

[woodenhead]

Well I am disappointed this evening.

 

Thought I had space to pop in a little OO roundy roundy for simple freight operations into my office/layout room.  I now remember why I model in N.  So the available space will at best allow me 2nd radius curves and with that it is eating into the space whilst at the same time wasting space - and no space for anything beyond a simple loop and a fiddleyard down one long side.   The plan sp far on XTrackCAD actually is just under the second radius at 89cm, so it actually needs to be widened meaning even less.

 

It would have been nice to have done something so I could use my stock, but I guess not.  Maybe if I want roundy I rebuild the N as such, that would be a nice space for  2 track mainline without taking up as much real estate within the room.  OO will remain a pipe dream / small affair.