Scale

[Bruce EdneyParticipant @bruceedney59949]

Hi

Being new to model engineering I am wondering if someone could please explain model scaling. I get the 1:48 type (1 inch in model = 48 inches in full size) scaling but how does the 3" scale (and the like) for a traction engine work?

Thanks in advance

Bruce

[Bruce EdneyParticipant @bruceedney59949]

[Thor 🇳🇴Participant @thor]

Hi Bruce,

Have you read this explanation here for locomotives?

Thor

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Bruce Edney on 18/04/2015 03:49:03:

… but how does the 3" scale (and the like) for a traction engine work?

.

Bruce,

I'm sure that JasonB will correct me if I'm wrong:

It's simply a matter of adding the phrase "… to the foot"

MichaelG.

[Bruce EdneyParticipant @bruceedney59949]

Ah that makes sense

Thanks guys

[IanTParticipant @iant]

In terms of taking a full size "drawing" and scaling it (for instance for traction or stationary engines) – Michael's "to the foot" is absolutely correct. This is also exactly true for railway locomotives but there is very often a mismatch between the scale used for the engine versus the track gauge being used.

So for anyone trying to model railway stock "to scale" then (and sorry Thor) the Wikipedia link provided gives (I think) a very poor explanation of how railway "scale" should be calculated.

Historically, the 'scales' used in both the smaller and larger model gauges did not closely relate to the prototypical gauge being modelled. They were simply rough approximations. For instance in the link – 1/24th 'scale' is mentioned. This was the original 'scale' used for 2.5" track (Gauge 3) but actually a much closer measure (and the one used these days for standard gauge 2.5" models) is 17/32" – and when you see vintage 1/2" stock besides modern 17/32" stock you can see a real difference.

The only correct way to calculate the correct scale is to divide the model track gauge into the prototype track gauge. So a standard gauge engine running on 2.5" track should be built to a ratio of 1:22.6 (e.g. 56.5"/2.5"  which is actually very near to 17/32 (or 13.5mm if you prefer). For a narrow gauge engine – then simply use the original gauge used (24", 36" etc.) to achieve the same result. So a 2ft N/G engine on 2.5" track should be built to a scale of 1:9.6 (1.25" to the foot).

Sorry to bore anyone out there who already knew all this (or simply wasn't interested) but it's something that seems to confuse a lot of people and there's quite a lot of misinformation floating around out there on the web in this area.

Obviously two mugs of coffee is too much for at this time of day! Must be Shed Time!

IanT

 

Edited By IanT on 18/04/2015 09:23:02

[RobboParticipant @robbo]

What is confusing is the use of the word "gauge" to refer to both the scale of a model and the size of the track width.

The two do not correspond, eg 16mm gauge models don't run on 16mm gauge track.

[IanTParticipant @iant]

Well – It seems to confuse a lot of people Robbo.

One way to think of it – is that all full sized engines were built to the same "scale" (e.g. 12" to 1 foot) but that they ran on a number of different track "gauges" (e.g. standard, narrow and broad gauges). The two measures are quite different really.

For any railway model to be accurate in scale terms there should be a close relationship between the 'scale' used to build the model and the track 'gauge' it is going to run on (or be associated with)

"16mm" is simply a catchall expression to describe narrow gauge models that generally run on 32mm or 45mm track – but the prototype N/G gauges varied somewhat, so 16mm engines tend to be very much scale approximations in many cases.

In Gauge '3' – we model standard gauge prototypes on 2.5" track, so there is not the same room for any confusion – the scale ratio is very clearly 1:22.6.

As perhaps an interesting aside (?) when I used paper & pencil to draw my models, I worked to 13.5mm to the foot to convert things to "scale" – very close but not exact. Now I use CAD – I can draw at "full size" and then scale everything exactly using a ratio of 1 to 22.6.

I was involved last year (with other G3S members) in developing a low-cost G3 battery electric 'Sentinel' kit. I did all the CAD work for it and it was quite pleasing somehow to be able to tell people at the AGM that it was built "exactly to scale" (OK – I'll admit small things do please me)

Regards, IanT

PS Unfinished prototype Sentinel kit at G3 AGM in February.

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