Hi Will
Will L wrote:Julian Roberts wrote:P4 has 12% extra slop built in to it, but roughly half of that extra slop disappears on curves - just when we need it most.
Julian, I think the point you are missing may be that the 12% extra slop is all about the practicalities of making functional point work easier and nothing at all to do with the need for gauge widening. However once you’ve got it, the need for gauge widening is less.
OK if, for the purposes or modelling veracity, you want to replicate prototype exactly then that is your right. But, despite the rhetoric, the P4 standards are not an exact scale reduction of the real railway. They are actually a practical working set, proven over time to work and for the generality of users don’t need the tweaking you suggest.
Hi Bill
If you want modelling veracity, and you want to replicate prototype exactly then surely you should be modelling in S4?
Thanks for your thoughts!
Problem with a Forum is to have to keep repeating myself. No, I am not wanting to go S4 nor replicate the prototype just for modelling veracity, the issue here is completely invisible and totally minute, we are talking here the equivalent of how many angels can dance on a pinhead, a difference of 0.1mm at a curve of 4' 6".
What I am trying to talk about making things easier for ourselves. An equivalent in music is that when there is a very difficult passage with a lot of notes, in their anxiety people tend to rush as they get near the passage, so that means they've got to play them even faster. Music is a bit like the circus, making things look or sound easy that are really very difficult. Practising to perfection is a lot about learning to give ourselves room, or find tiny ways to make it easier.
There is 12% more slop in P4 but about 50% less gauge widening on curves. So we give ourselves more room with one hand, and then take half of it away with the other! Many people here have said they were unaware that it was the case, that the P4 gauge widening is 50% less. Did you know?
Yes lots of people make it work - but I bet there are lots of others who can't, and give up, or try EM flanges etc, that we don't know about. P4 still has an air of mystique about it, as it were the icy mountaintop of 4mm modelling. People like you, Keith, Allan, Tim Venton are master modellers. But one sees lots of references to "running was improved" by such and such a tweak from ordinary mortals! - people are always looking for ways to improve the reliability of running, surely.
As far as I can see by looking at the graph (that originally Alan Turner came up with) and figures, the gauge widening standard is predicated on a toy train minimum radius of 21", from the days 50 years ago when such a curve was more normal in modelling. I wonder if it might have been to do with the EM standard which is 0.2mm at 610mm radius. Their triangular gauge is just 1mm shorter.
But you say it was intentional for the kind of radii we normally work to, 4ft minimum the general recommendation.
The thing about this is, that the gauge widening progressively gets wider as the radius decreases, so a 50% difference is a gradually increasing figure. Meanwhile the 12% extra slop figure stays constant. This means that gradually the P4 slop completely disappears, so that by the time we are down to 4 foot radius the Running Clearance is starting in some situations to be
less than the prototype. So, relative to the real thing, as the track curve incresases the rails become tighter and tighter on the wheels.
It is all obvious if you look at the graph - the blue line (for the Society standard) and yellow line (that represents the averaged out prototype) diverge as the radius narrows. Both these lines were made up by Alan - they both require a tiny bit of correction, but the message will hardly change:
Gauge Widening Graph 1.pdf
I don't know how to convert these files to PDF which would make them visible here - but here are photos of the pc screen
2016-08-08 09.29.03.jpg
The spreadsheet gives numbers:
Gauge widening Spreadsheet.xlsx
2016-08-08 09.31.32.jpg
I've done some maths from the spreadsheet and the Track and Wheel Standards. Here are some running clearance figures. As BB is expressed as a range (17.67-17.75 in P4, 17.87-17.89 on the prototype) there is an analagous range to the figures:
PROTOTYPE with prototype gauge widening*****************P4 with Society Gauge Widening***************P4 with prototype gauge widening
Straight track: 0.18 - 0.2***************************************0.28 - 0.36****************************************0.28 - 0.36
8 foot curve: 0.283 - 0.303*************************************0.325 - 0.405*************************************0.383 - 0.463
4 foot curve: 0.3844 - 0.4044**********************************0.3694 - 0.4494***********************************0.4844 - 0.5644
Edit: As these numbers go out of place on my mobile phone here are the figures handwritten as a table, which I don't know how to do on a pc:
Running Clearance in P4.jpg
[Well I don't know if my maths is correct. Example: For P4 straight track 18.83 - 17.67 (BB) - 0.8 (flanges x 2) = 0.36. Or with 17.75 BB the result is 0.28] [Prototype at 4 foot: 18.83 + 0.2044 (widening for 45 mm tool) = 19.0344. Minus BB 17.87 and two flanges 0.38 each = 0.4044. Or with BB 17.89 the result is 0.3844)]
The P4 BB, using prototype gauge widening, would keep the Running Clearance comfortably above that of the prototype.
Obviously a wider gauge of, for example, 0.1mm at 4' 6" is hardly going to make a vast difference. Of course it doesn't mean you can do without adequate sideplay, compensation or springing, all the things necessary for proper running. But might it be a tweak (and no more) that the generality of users could benefit from? It doesn't imply any criticism of any other aspect of the standards - at least not as far as I know.
Things have come on a lot in this hobby in the last 50 years. People always argue against change on the grounds that things are perfectly good as they are. Increasing the length of the triangulation would not change anything else at all in the standards. The difference it would make is minute. Not worth the effort of writing this probably...
However, just to return to a bit of sanity and reality, Richard Chown, got back to me (thanks Richard!) with the information that the curves I mentioned, at Carstairs and Cowlairs, are far less sharp than I was expecting - around 10 and a half chains at Cowlairs, more at Carstairs with various other considerations. So these sharp curves being discussed above are way out from being realistic - but that doesn't mean we never use them.
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