Can anyone answer this riddle?

[Julian Roberts]

In the thread "Society Gauge Widening Tool" viewtopic.php?f=5&t=4732 I have been asking a question:

Why is our Gauge Widening Standard 0.22mm at 528mm?

The 0.22mm is the easy bit - it's the scaled down prototype figure minus 12%. But why at 528mm, much less than half the prototype's?

If you have not seen or looked at the thread, and have an answer, please reply on that thread. If you don't have an answer but are interested please look at that thread, don't reply here.

2016-08-17 00.02.12.jpg

[Martin Wynne]

Hi Julian,

528mm is 2 chains radius (scale).

You have to remember that those dimensions were compiled over 40 years ago, when prototype info wasn't so widely known. If you read the old articles you can find several questionable details quoted. If you are looking for perfection in some of the early standards you will be disappointed. For example you can see switch back clearance quoted as 3" (1mm) when it should be 2"(0.67mm).

My guess is that someone had some pre-group info relating to gauge-widening on a specific company, where 2 chains was the bottom limit. Also the 3/4" maximum widening was not always so -- in some cases 5/8" or 11/16". For example on LPTB lines where main line locos also run, max gauge (below 5.1/2 chains) was 4ft-9.1/8in, i.e. 5/8" widening over standard gauge.

I think you are looking for an explanation which doesn't exist -- the standard is just plain wrong, that's all there is to it. More to the point, what is your actual modelling problem?

Note that the model 3-point gauge has no prototype equivalent. Check rail chairs were made in a series with increasing flangeways, typically 1/4" increments. So gauge-widening had to be one of those steps and fixed. It wasn't infinitely adjustable, except where there was no check rail -- which wasn't often because curves under 10 chains radius on passenger lines are required to be fitted with a continuous check rail.

p.s. Just noticed that you don't want me to post this reply here. Why not? Self-appointed moderators make me see red. But I will copy it there for you.

regards,

Martin.

[Martin Wynne]

I have now found the 528mm dimension in the EMGS standards booklet from 1970:

emgs_standards_booklet_1970_1.jpg

emgs_standards_booklet_1970_2.png

Quoted at that time as "the minimum recommended radius for satisfactory running" in EM. Some today may regard 21" as well below the sensible minimum. Times change.

Martin.

[Julian Roberts]

Stunning detective work, Martin!

Three cheers!
Let the discussion continue over on the other thread...




viewtopic.php?f=5&t=4732