4mm Scale Dimension and Clearance Drawing

[Steve Crow]

Hello, this is my first post so this is probably in the wrong place.

 

Planning for a future project, I attempted to find dimensions, scale and prototype, for structure and platform clearances etc.

 

I found a few different sources (often contradictory) but they were scattered over many sites.

 

To this end, I've attempted to combine all the information I could find into one scale drawing that fits on a A4 landscape sheet.

 

I would really appreciate it if anyone can error-check this. Also any additions or ammendments would be welcome so I can keep updating the drawing.

 

Cheers,

 

Steve

[Stephen Freeman]

So many different dimensions over all the Companies in the UK, it's much easier, at least for the track to use Templot.

[Steve Crow]

1 minute ago, Stephen Freeman said:

So many different dimensions over all the Companies in the UK, it's much easier, at least for the track to use Templot.

I have been learning to use Templot for a few weeks now and find it very useful but it doesn't help with things like structure clearances etc.

[Stephen Freeman]

1 hour ago, Steve Crow said:

I have been learning to use Templot for a few weeks now and find it very useful but it doesn't help with things like structure clearances etc.

If you use the clearance tool (forget the proper name at the moment) but once set with vehicle dimensions (dummy coach?) you can roam it along the track to check for any conflicts.

[Michael Hodgson]

There are a lot of different profiles and clearance specifications for this on the prototype, but regardless of what profile of vehicle you are using, you will need to allow for overhang/underhang of bogie vehicles on curves, and the degree to which the stock encroaches increases as  the radius of the curve gets tighter.  As we model unprototypically tight radius curves, scaling up from official documents doesn't help.

It can all be calculated mathermatically, but in practice it is much easier to select your most awkward coach (possibly the longest) and gauge you clearances against that by running it round the layout - if coach X can clear it, eveything will.

[Steve Crow]

I appreciate that compomises will need to be made with tight track geometry.

 

I should have made it clear on the drawing that nearly all dimensions are minimum.

 

What I was trying to achieve was a sort of guide - a starting point for representing the prototype in P4.

[Steve Crow]

I have amended the drawing and re-labeled it to make its purpose clear.

 

I would still appreciate it being error checked. There has to be some...

[Izzy]

On 01/11/2023 at 11:38, Steve Crow said:

Planning for a future project, I attempted to find dimensions, scale and prototype, for structure and platform clearances etc.

 

I found a few different sources (often contradictory) but they were scattered over many sites.

 

Doesn't the Scalefour society provide these details? They used to at one time. Anyway, back in the '80's I drew these up for a magazine article I wrote. They were drawn up with full size measurements as these are easier to convert to whatever scale is being used, 7mm, 4mm, 2mm etc. I have put them on RMweb before but forget where now but perhaps they will help you in your particular endeavours. 

 

 

 

 

Bob

 

 

[Steve Crow]

Thank you. I'd looked at the Scalefour society but didn't see these.

 

My measurements seem to broadly agree with yours so that's a start.

 

Steve

[Miss Prism]

Scalefour Digest 62.0

 

(assuming it still exists!)

 

[Grovenor]

https://www.scalefour.org/members/digests/dl.php?f=62-0v1-2.pdf

But you need to be a member.

This one is public,

https://www.scalefour.org/p4-standards/

 

Better clearance info will be found on the back page of this,

https://www.railwaysarchive.co.uk/documents/MoT_Requirements1950.pdf

Edited November 3, 2023 by Grovenor

[bécasse]

There is a useful introduction to the great variety of different loading gauges that the big four inherited from pre-grouping companies here. 

[Typographer]

If I may, I think referring the Steve to various sources, though very valuable, might not be what he is asking for. It sounds to me like his diagram requires an old-fashioned proofread, to catch transcription and other errors. It’s very difficult to proofread a diagram you have yourself compiled and designed (you see what you think is there, not what is actually there). But a proofreader needs to read against copy. So if Steve gave the specific sources for the various figures he gives, then perhaps someone out there might double-check them against those sources…

[DCB]

I like the idea of a set of 4mm dimensions but a set to suit Ready to Run rather than scaled down full size or Scalefour.    Passennger Platforms are 3ft or 12mm above rail level  MAXIMUM. Using modern Bachmann / 1970s Airfix 1950s  Horrnby Dublo etc.  stock  (Hornby are all over the place   derived from Triang)  Steam age platforms are often a lot lower and steam era platforms are still common in rural Scotland  and elsewhere.especially heritage railways   Coach floors are significantly higher  than platforms, I would say 80% of model platforms mine included are too .high   

Buffers a tad under 3ft 6" (14mm centre line to 3ft 3"  () 13mm) when springs are worn and stock heavily laden.  (Hornby are often far higher.

RTR OO Locos are up to  40mm wide (10ft)  (9F)  and 9ft near rail level (8F)  and 60mm High 15ft   (Various GWR Tanks)  against 9ft and 13ft 6" scale      BR Mk1s are 9ft 3" (37mm )  and Centenaries 9ft 6" (38mm) wide

Track centre lines should be gauge (19mm) plus 6 feet (24mm)  which is 43mm,  That is a good figure to use  on straight track,  It's what I aim for. OO  Peco is 2" or 50mm spacing  Set track  about 65mm or more.
I might nick your ideas myself and add  under throw and overthrow figures for structures on various radii, or maybe not...

[Izzy]

3 hours ago, DCB said:

 

Track centre lines should be gauge (19mm) plus 6 feet (24mm)  which is 43mm, 

You’re not allowing for rail thickness which with 4mm code 75 bullhead is around 1mm so 45mm is correct, 4 x 11’ 2”. The ‘six foot’ between the outside faces of the rail is just the - minimum - straight line distance that results when the correct gauge is used. It will increase with both track curvature and elevation to allow for end swing and chordial differences. It will also increase with under correct gauge model track which is why going by centre line figures is better/easier.
 

Bob

[DCB]

# Izzy you are right.     I was allowing for rail thickness but in OO (HO) gauge as Peco OO/HO is HO scale track.   P4 EM will look good at 45mm.  OO (HO) should be  19mm + 21mm 40mmish  (for the UK) to look good with 16,5mm gauge but 9Fs and the like will not clear each other at 40mm.   As long as the trains don't actually hit each other the closer the better on the straight for ordinary double track  appearance with OO.  hence 42/3/5mm is better than 50/2 or 60mm     Loops or third tracks which had 10 foot spacing look good spaced 60mm centre lines, Its's something I got wrong and am currently very slowly rectifying on my layout. I use test stock for setting  curve spacing and I don't allow for movements I never make.   A Hornby King leading end throws several millimeters less reversing round a curve than going forward so mine hits the platform on the crossover going forwards, but it never goes across forwards, its always reversing out so it clears,    My Class 156 and M3 sleepers on the outer radius wont clear the King on the inner. Not an issue as they are different time periods and don't run together.   I think you are looking at another 5mm spacing or maybe more if you want a King and a Mark 3 to pass on 3rd/4th  radius compared to a Castle and a Collett 60 footer   I had to chop away a lot of Cotswold stone on the outside railway when I introduced a class 156  to a formerly class 37 and Mk2 coach railway so small differences in throw and length make big differences on curves.

Edited November 5, 2023 by DCB

[Stephen Freeman]

On 03/11/2023 at 15:16, Miss Prism said:

Scalefour Digest 62.0

 

(assuming it still exists!)

 

It does, members only though.

I have discovered thanks to Martin Wynne, that in Templot, you can specify a dummy vehicle dimensions and it will show you an "envelope" along the selected track which will show you the clearances necessary, at least as far as any lineside features such as platforms, though of course matters of height are another matter. The correct spacing for standard double track in 4mm is 44.67mm, though how much double track should be to this measurement is another matter. Former Broad Gauge lines probably more generous as station areas and yards etc etc. Templot is very helpful here.

[4700mm]

I'm only an OLE person so not competant to comment on most of the dimensions but I noticed you're missing the dimension of the running edge to the platform offset which group standard GIRT7020 gives as 730-745mm for most locations. Scaling that down should be fine for P4 but would need to be increased for curves.

[5BarVT]

On 05/11/2023 at 16:42, 4700mm said:

I'm only an OLE person

I wondered whether your username had significance . . .

:-)

Paul.