7mm Flangeways for 31.5mm 0-gauge track

Dog Star

Western Thunderer
Chris Brown (@ChrisBr) and I are interested to understand the clearances used for turnouts which are built for "31.5mm" gauge; that is:- the flangeway between the Vee and wing rails of a common crossing... the distance between a stock rail and an adjacent checkrail at the 'CC' chair positions... and the clearance between the end of a switch rail and the adjacent stock rail.

If there is a standard, or preferred, value for these dimensions then what are those values and from what source?

In practice, what values are used by modellers of the "31.5mm" persuasion?

thank you, Graham
 

martin_wynne

Western Thunderer
If there is a standard, or preferred, value for these dimensions then what are those values and from what source?
Hi Graham,

I suggest you use the dimensions given for 0-MF in Templot -- 31.5mm gauge with 1.5mm flangeways. This gives a check gauge of 30.0mm min, a convenient round figure to remember and work with.

0-MF (31.5mm gauge) is a good compromise for use with the widest possible range of wheels, and is now being widely adopted. It allows for a flange thickness up to 1.0mm for traditional 0 gauge wheels set to 29.0mm back-to-back. For "industry-standard" Slater's-type wheels at 29.2mm back-to-back, flange thickness can go up to 0.8mm max. Check span is 28.5mm matching G0G-Fine, allowing a good clearance under BB on sharp curves, and a practical tolerance up to 28.6mm. The 1.5mm flangeway plus prototypical 3/4" blunt nose gives a minimum wheel width for full support at crossings of 3.4mm compared with the G0G-Fine minimum wheel width of 3.5mm.

In summary, your track gauge tools need to produce track as follows. It is always preferable to have a check gauge tool separate from the track gauge tool, and to set the crossing flangeway (but not the check rail flangeway) with a suitable feeler gauge or precision shim.

track gauge 31.5mm minimum
check gauge 30.0mm minimum
check span 28.6mm maximum
crossing flangeway 1.5mm maximum

regards,

Martin.
 

Steph Dale

Western Thunderer
Graham,

This is something the Guild were looking at when I was leading the Technical Committee. With luck Richard will be along in a minute with an update and the benefit of his experience building and operating a layout to this deviation.

Steph
 

Dikitriki

Flying Squad
Hi Graham,

I used the dimensions Martin has given in his post. In fact I checked them via the Templot club before I did anything. The only thing I would add is that the clearance between switch rail and stock rail was a minimum of 3mm. I sometimes found, if the switch rail was particularly flexible, that I needed a little more to avoid the back of the wheel just kissing the outside of the switch rail further along, but each clearance was set by empirical testing. Remember my Switch rails were continuous rather than split/hinged/whatever the correct expression is.

Richard
 

martin_wynne

Western Thunderer
Hi Richard,

The scale switch opening at the switch blade tips is 4.1/4" = 2.48mm for S7.

To look the right curve on a flexible switch blade, it needs to open by about 2.4 times the flangeway gap, which for 0-MF would make it 3.6mm.

However, that would probably look a bit much in relation to the track gauge, so I suggest 3.0mm as a minimum 0-MF opening, as you found.

Alternatively, it needs to open by a scale 2.5" more than the flangeway gap, which for 0-MF makes it 2.96mm. So again 3.0mm is about right.

p.s. "split/hinged/whatever the correct expression is" = loose-heel. :)

regards,

Martin.
 
Last edited by a moderator:
Top