Thanks for your reply a couple of days ago.
Alan's graph (April 22nd) shows that a track gauge 45mm long (whether triangular, rectangular, or 'Mint'), 50% longer than the Society gauges, is the length needed to give minimum prototypical widening. The 54mm I had suggested I now see is a maximum.
Although he says it is a simple calculation, I have not the skills needed to fill in the graph to show how far away our 29.75mm gauges are from his minimum.
Regarding what you said,
One of the objectives of the P4 standards is to have a consistent set which ensures that locos built to P4 standard will run satisfactorily on P4 layouts.
While I would admit to coming from the "getting at all right"tendency and thus suspension free vehicles and over size flanges are not my thing
please can I assure you that I am in exactly the same boat as you are. But, if you don't mind bearing with me, it seems to me that there is not a very consistent P4 approach on gauge widening, except the standard of 0.22mm maximum. Nor is there official endorsement of the gauge widening tool. If you look at the Scalefour Digest 1.2 Track and Wheel Standards, it has below the table of standards, and note the asterisk:
* These dimensions are controlled by construction gauges.
The asterisk, which appears by the track, check, and crossing flangeway dimensions, is absent from the gauge widening dimension. Somewhere on this Forum Russ Elliott says about the gauge widening tool something along the lines of, "the accuracy of the use of these artefacts cannot be verified"
Edit: I am misquoting Russ here. He says:
and ultimately it depends on the inherent accuracy of a check gauge, which is unknown since the accuracy of those artefacts is impossible to validate.
See his post on May 5 2012 atviewtopic.php?f=5&t=2021&hilit=gauge+widening+through+the+crossing
End of edit.
I have only recently gone into track making and was perplexed (meaning confused) about different approaches to gauge widening, as not everyone uses the triangular gauge. Looking at the website, it looks as though there have been some changes over the years on the issue. If you look at the Protofour Manual "Gauges for Tracks and Wheels" athttp://www.scalefour.org/history/p4gauges.html
you can see that the triangular track gauge (that in this conversation everyone is taking for granted as being the
way to make curves), was called the Mark 1 track gauge, but was superceded by the "much improved" Mark 2 pattern, the Mark 1 referred to as being "no longer in production". In what sounds rather clunky to me, as though reflecting quite some debate and perhaps a committee form-of-words agreement, there is the statement:
If it is accepted that virtually all curves on a model railway are to radii below the minimum value of the prototype equivalents, it is logical as well as convenient to apply maximum gauge widening in all cases where track is curved. To convert the Track Gauge for use on curved track (Fig. 4), a washer 0.2mm thick is inserted between the spacer and one bush. This is the Gauge Widening factor. It is desirable to maintain two TG and two TG+GW units ready for use when large runs of track are to be made.
A quite different scenario! But how the C&L or Exactoscale Fast Track comes, 18.83mm for straight, or +0.2mm for curved track.
From here on gauge widening is no longer automatic, it is a choice, as although the Manual says
all cases where track is curved.
the question may well be asked, when is a curve just a deviation, and when is it sharp enough to merit gauge widening?
Then one reads the Scalefour Digest 1.2 where it says
Where applied to non-pointwork curves, prototype
gauge widening at 10 chains radius is 0.25in, at 7
chains radius is 0.5in, and at 5½ chains radius is
0.75in maximum. (In 4mm scale, 1 chain is equal to
264mm, or approximately 10½in.) In P4, where
BBmax is less than the 4mm scale equivalent, and
where adequate sideplay can usually be given to
inner axles, gauge widening should not be necessary
unless using long-wheelbase stock around sharp
- and here it looks as though what has become a question, do I need gauge widening, that should have the default answer, yes, now has the default answer, no.
The question is begged, and not answered, how long is long (wheelbase), and how sharp is sharp (curves)?
After many years of modelling stock, mostly locomotives, nearly 10 years in P4, I don't take anything on trust. My first effort at compensation and scale wheels, admittedly in 00, resulted in a loco more prone to derailment than before, and for my first chassis in P4 I used the P4 spacers made by the same manufacturer and ended up with not enough sideplay. I realized the need to understand what is going on in order to fix the problems, preferably before starting.
To me as a fairly seasoned Scalefour Society member, starting to make some track, I look around for instructions, and those two Protofour approaches, and the Scalefour Digest are the three.
One has variable widening, one has the whole lot at once, and the third has none at all.
The only other source of instruction on the website is Keith's article in "Starting in P4" which shows the Mark 1 gauge in use. It would be a lot simpler if this had always been the only method.
It was in this context that I came across Russ's statement that is the opening post of this thread, and this put another layer of questioning into the mix, raising a doubt, confirmed by Alan's graph, over the most promising of the three approaches.
Keith wrote to me near the beginning of this thread
The P4 standard has a slightly reduced back to Back and slightly wider flangeways than an exact reduction from the prototype (hence leaving room for the really keen to 'correct' this). This is intended to give a little more tolerance in construction and has the effect of reducing the need for gauge widening.
If we can accurately locate the wheels as per the Scalefour standard, they are between 17.67 and 17.75 apart. The prototype “window” is between 17.87 and 17.89. Thus while our wheels may be as much as 0.22 narrower, they may be set only 0.12 narrower than the prototype. Quite close to the wind as the prototype widening gets to 0.2mm if we put in only 0.1mm?
Paul Townsend's reply regarding his use of the 35mm Mint Gauge shows that his P4 world does not implode nor do his trains fall inside the tracks. Alan Turner's 45mm length gauge would have a minimum usable radius of about 3 foot 3 inches before going outside the prototype 0.25mm maximum, or around 3 foot 11 inches to stay within the 0.22mm P4 standard.
I rather think that a desire to be pedantic about the prototypical use of gauge widening
I am not trying to be pedantic, sorry if it comes over like that. Like you, I am of the "getting it all right" fraternity. Rather, my gist is that surely we are asking for trouble giving ourselves less leeway or extra room on curves than the prototype, and this might partly explain P4's reputation in some quarters as not being reliable. We might find it easier to get reliable running if we took more heed of the prototype surely?
But the main point of all this is to provoke debate and learn something: most people did not know the Society gauge only gives around half the amount of gauge widening (more exact figures hopefully will emerge from somewhere): and no one has come up with a reason that the P4 maximum gauge widening is 0.22mm rather than the prototype maximum of 0.25mm, though obviously the difference is simply a mathematical rather than practical one.