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having had a look....NEM #112 gives the recommended spacings, from track centre-line to track centre line, as 46 [mm?] for 'open country' track..and 52 [mm] for yards/stations.

This is for HO.

The distences [from centre line to centre line of each adjacent track] for curves are also outlined....but subject to various criteria.

These criteria are to be found in NEM # 103.

They seem to be......based upon the LENGTH of vehicles used...and these are defined as A,B,&C

What you need to do is MEASURE the length of the LONGEST vehicles you will be using...[ie coaches]

Then compare those lengths with the table on NEM# 103....obviously looking up under the SCALE you are modelling in...[I assumed HO?}

having decided which letter applies to your stock.....you then refer back to NEM#112......which will give you the separation distance...ON CURVES....for the radius of your curves..[referring to the minimum..or sharpest radius you are using]...and the category your longest vehicles fall into....

.for example, if your longest stock falls within category C, and your tightest radius on a curve happens to be 500mm...in HO your centreline spacing will be opened up to 59 mm.

to find out how much CLEARANCE you need to leave...OUTSIDE and INSIDE each curve...you need to refer to table E, on NEM# 103.

again, table E gives you your radius for the curve..and you cross reference that figure, with teh category [A,B,orC] that your longest [coaches] fall into....this gives you a value.

for example, if your coaches fall into category C for length...and the radius of your curve is 500mm.....then cross-referencing gives you a VALUE of 11 [for HO]

now, going to the bottom of page 2, NEM #103.....there is a dsiagram showing how the clearances outside the track line are measured.

the width of clear space required on your curve, is noted at B(1) +2E.

Going to the top of page 1, NEM#103, another diagram defines B(1)...this value is the WIDTH of your coaches [or stock, if using wagons only]....this MAY vary according to age of prototype...or fidelity to scale of your models.

so..to find out how much space to leave outside and inside your curve.... add B(1) dimension to 2X value of E.

thus, in my example......the value of E was 11.....so....the overall amount of clearance needed on our 500mm curve, for a coach in category C [length]...is......2x11 + the width of those coaches.
 

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nip down to a dealers shop with a tape measure......if you currently don't have any stock?

In the bad old days, I used to lay out the curve [track], find the longest coach[with the longest overhang beyond the bogies]...with fingers, clamp a felt tip of suitable colour to an outside end, and push the coach around, marking the board. This gave the minimum outside clearance......then I'd clamp the felt-tip to the centre of the coach, on the INSIDE of the cure, and do similar.

Anything of height within those two lines will get clouted.

For my son's OO gauge layout, i tried to steer him towards short, bogie coaches, due to limited space.....he wanted an autocoach, and this became the marker coach, [hornby]...since it had so much overhang, compared to Thomas stuff...and Bachmann Mk1's...
 
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