Track Gauge Widening, All You’ll Ever Need to Know

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Paul Townsend
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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Paul Townsend » Mon Aug 29, 2016 6:34 am

Jol Wilkinson wrote:Will,

those strange 8 wheel LNWR 42' carriages incorporated radial axles at the outer ends, so benefited from a small degree of "flexibility". They were also mainline stock, at a time when carriages for the lower classes daily travel were either six or four wheeled, so they were unlikely to encounter too many sharp curves. Some were later converted to bogie underframes.

Jol


GWR in Broad Gauge era around 1880s also had some 8 wheel rigid underframe gauge convertible carriages around 40 ft eg E3. The Broad Gauge Society kit F60 for the underframe has inside hidden bogies to make it a practical model. Dean converted these underframes to bogies and then they were narrowed.

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Will L
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A Final Conclusion

Postby Will L » Tue Aug 30, 2016 4:12 pm

As it should now be clear that applying gauge widening may well be unnecessary for many of us, perhaps we should take seriously the prototypical injunction that gauge widening through point work should be avoided.

If you have read this far you should now be able to find out if your circumstances are going to require Gauge Widening (e.g. you really do want to run Black 5’s over A5 turnouts, or shunt that gasworks siding with one). If for you gauge widening isn’t necessary then don’t let a 3 point track gauge near your point work, and much of the complexity in the P4standards, introduced to ensure the check gauge through the common crossing is right in the presence of gauge widening, goes away.

Just to help with those who do have very sharp curves “behind gas works”, I have replotted the Gauge widening required for specific loco wheel bases down to a 550mm curve (between 1’ 9” and 1’10) with 0.8mm end float on the centre axle. (0.8mm on the grounds that while we might be aiming for 1mm we don’t always achieve quite what we aimed for).

On this basis gauge widened points should be very thin on the ground.

Ext P4 loco comp with EF..jpg
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Will L
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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Will L » Tue Aug 30, 2016 4:27 pm

A question for the experts

Despite everything I have said so far, I have been a few comments which continue to suggest that long wheel base 4 wheel vehicles require gauge widening. I think this is not true, but it you think otherwise please explain why so we can come to an agreement about what is right.

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Julian Roberts » Sun Sep 18, 2016 5:49 pm

The Rice Diagram. 

I don’t have access to Ian Rice’s work on track so I’m not quite sure what he said, but quoted in isolation like this, it is, at best, misleading. The Clearance between track and wheels we have discussed before is sufficient to ensure that there will always be space between wheel and rail, whatever angle they are to each other. This is why a 4 wheel vehicle never requires gauge widening. 


I hope nobody thinks I enjoy being argumentative Will and that is the reason I procrastinated this post. I am not wishing to comment on the following. The relevant part of Iain's book "An Approach to Building Finescale Track in 4mm" says:

RUNNING CLEARANCE
There is , of course, one further consideration to be recognized in the search for the Elysian 'friction free' running of our stock, and that is the matter of 'running clearance' or 'flange clearance'. Reference back to good old Figure 1 will show that the outer faces of the flanges of our wheelset do not touch the inside faces of the running rails, by an amount (surprisingly small in full size practice; I was amazed how many PW dimensions are quoted to 1/32 of an inch) that is sufficient to ensure that, under normal conditions, the action of the coning already described can keep the flange face clear of the rail.

This is a simple enough consideration on straight track but, as usual, as soon as you get to a curve, problems arise. Consider Figure 3 for a moment [this is the picture I posted earlier] which should show how the fixed wheelbase of a railway vehicle (and even a bogie has a fixed wheelbase of quite significant length in this context) can all too easily take up the running clearance when a curve is encountered. I've noted that this clearance is quite small, to prevent vehicles 'hunting' on straight track under some conditions, so it doesn't take much of an 'angle of attack' between the wheel flange and the rail to use it up - when instant friction will result. As the wheels cannot move on their axle to maintain the necessary clearance, this is achieved by easing the track gauge, by an amount dependent on the severity of the curve.

The finer modelling standards....require provision to be made to introduce gauge widening on curved track, one of the factors taken care of in the proper design of track gauges.

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Will L
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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Will L » Sun Sep 18, 2016 11:43 pm

Julian Roberts wrote:I hope nobody thinks I enjoy being argumentative Will...

No I assume you just want to be clear.
The relevant part of Iain's book "An Approach to Building Finescale Track in 4mm" says:

RUNNING CLEARANCE
See above


Then I'm afraid I'm going to have to disagree with our Mr Rice's writen words as well as the diagram. A quick read of the Malcolm Cross article which Keith pointed out some time ago here is informative. While written to cover the issues met with 6 wheel stock it does cover the implications of the outer wheels of long fixed wheelbase because 6 wheel vehicle are, by their nature, long. This article points out that they key element is the angle of incidence between wheel and rail. This is determined by the radius of the curve and the vehicle wheelbase and is unaffected by any gauge widening note. Mr Cross points out that for angles of incidence of less than 3 degrees the shape of a flange ensures it will not come in contact with the railhead in advance of normal the low point.

If the magic three degree figure is exceeded then the flange contacts the rail in advance of the normal point of contact, and we can expect running problems. Mostly this is the much increased likelihood of the wheel climbing the rail, but it is true that if an extreme angles is achieved then Mr Rice's fear will come true and there won't be enough room for the wheel set to fit between rails at standard track gauge. I haven't done the maths to work out exactly how much more angle produces this result, and few would enjoy reading it anyway. However before we get too excited about that possibility, the graph Mr Cross produced (reproduced in Keith's next post but not currently on the copy of the article on the web sit) shows that you that the 3 degree angle wont be exceed unless you want to run something more extreme than
Wheel base = Track Curve
10 ft round a 1'3"
20 ft round a 2'6"
30 ft round a 3'9"
roughly (assuming 6'0" foot wheels, a 3'6" wagon wheel would be more tolerant). I did do the maths on this one then realised that all I was doing was verifying the already published graph.

I.e This is a none problem. OK i suppose those of us running 22'6" wheelbase 6 wheel coaches need to be aware we will have problems getting then round anything less than a 3'0" curve without doing something un-prototypical to the suspension, but I strongly suspect the problems of rail climbing will become dominant long before an axle at an extreme angle to the track prompts a need for gauge widening.

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Martin Wynne » Mon Sep 19, 2016 2:08 am

Will L wrote:I.e This is a none problem........but I strongly suspect the problems of rail climbing will become dominant long before an axle at an extreme angle to the track prompts a need for gauge widening.

Rail climbing will never be a problem, because on curves sharp enough to cause it there will be a continuous check rail to prevent it. That doesn't remove the advantage of some gauge widening on such curves.

Arguing about the writings of modellers seems unnecessary when we have the prototype's words to fall back on. This is from BRT3 of 1964 (my red), repeated unchanged in BRT4 of 1971:

gw_brt3.png
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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Noel » Mon Sep 19, 2016 10:33 am

Will L wrote:Wheel base = Track Curve
10 ft round a 1'3"
20 ft round a 2'6"
30 ft round a 3'9"


This is a little ambiguous, Will. I assume that the wheelbase figure is the 'real life' one, so that in model terms the figures are 1.57" (approx) and 1' 3", etc.?

Will L wrote:I.e This is a none problem


If you take an extreme case, a 4-wheel vehicle with a 90mm wheelbase will not go round a 45mm radius curve. It will go round a 2000mm curve. Somewhere in between there must therefore be a radius at which the vehicle fails in some way to cope with the curve as its radius reduces. The question is at what radius does this occur without gauge widening and does it have any practical relevance? {If I have interpreted them correctly, your figures above suggest that it is potentially a problem with practical consequences.]

I note Martin's comment about check rails preventing the outer wheels misbehaving, but this only moves the basic problem to the inner wheels, as there will come a point where both flanges are against the running rail and the backs of both flanges contact the check rail.
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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Will L » Mon Sep 19, 2016 10:49 am

Martin Wynne wrote:Rail climbing will never be a problem, because on curves sharp enough to cause it there will be a continuous check rail to prevent it. That doesn't remove the advantage of some gauge widening on such curves.

Arguing about the writings of modellers seems unnecessary when we have the prototype's words to fall back on. This is from BRT3 of 1964 (my red), repeated unchanged in BRT4 of 1971:


All very well Martin but

1. We as modellers tend not to fit continuous check rails in the way you suggest, I assume mostly because it emphasizes the fact that our curves are too tight and it looks un-prototypical on what is supposed to be a bit of main line. Also Keith's explanation as to why the DLR reverted to fitting check rails, having thought they could do without, suggested a reason (wear effects on the outer rail) which are unlikely to bother us.

2. Most model practice (excepting S4) differs from prototype practice in one key respect, the degree of clearance see above, and it happens to be that this difference is the key operative factor here. This and our greater ability to provide increase flexability on central axles means that the occasions when providing gauge widening becomes desirable occur at difference stages than on the prototype, and makes prototype practice a poor guide. This thread has tried to show how this operates, was it wrong?

The whole drive of the correspondence which gave rise to all this was a view that "more would be better", while the facts seem to be that current practice provides more than enough, and the point work complexity of needing to carry gauge widening through common crossings is therefore largely (and prototypically) avoidable. I would have thought you would approve?

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Martin Wynne » Mon Sep 19, 2016 10:52 am

Noel wrote:The question is at what radius does this occur without gauge widening and does it have any practical relevance?

Hi Noel,

The factor missing from these discussions is the rail profile. Prototype BS-95R bullhead rail has a 1/2" top corner radius. Model rail sections are all over the shop in this regard. Clearly you can't calculate an incidence angle at which the flange will bind against the rail without knowing the exact profile of the flange, AND the exact profile of the rail head.

In practice P4 wheels go round curves down to about 4ft radius without any problems, and below that we add a bit of gauge-widening to help them along.

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Philip Hall » Mon Sep 19, 2016 11:06 am

Martin Wynne wrote:

The factor missing from these discussions is the rail profile. Prototype BS-95R bullhead rail has a 1/2" top corner radius. Model rail sections are all over the shop in this regard. Clearly you can't calculate an incidence angle at which the flange will bind against the rail without knowing the exact profile of the flange, AND the exact profile of the rail head.


When the MSRG started all this they recommended the only suitable rail at the time, the Kingsway rail from Model Railway Manufacturing at Kings Cross. This rail had a distinct radius to the head, unlike our present day sections which are much squarer. This also made it look a little lighter. I still have a few odds somewhere. I also have a view that as a little more of the rail is in contact with the tyre, slightly more reliable electrical contact might ensue. One particular railway I have seen (Churston) has this rail and doesn't need to be cleaned too much.

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Martin Wynne » Mon Sep 19, 2016 11:33 am

Will L wrote:The whole drive of the correspondence which gave rise to all this was a view that "more would be better", while the facts seem to be that current practice provides more than enough, and the point work complexity of needing to carry gauge widening through common crossings is therefore largely (and prototypically) avoidable. I would have thought you would approve?

Hi Will,

I'm not sure what you want me to approve?

1. I agree that the amount of gauge widening provided by the existing 3-point gauge tools at around 30mm long is sufficient for running lines. Gasworks sidings may need more if you are going to run pacific locomotives in there.

2. I definitely don't agree with the advice in the P4 standards not to apply gauge-widening through ordinary* pointwork. Nor does it add much "complexity" -- the check rail flangeway gap simply increases by the same amount as the gauge is widened.

Even a nice gentle generic B-7 turnout has an inner radius of around 40" when inserted in an 8ft radius curve. If some gauge-widening is needed on 40" radius plain track, it is obvious that it will be needed on the same radius within pointwork.

It's true that over the short length between the knuckle and the start of the wing-rail flare, a wheelset will see no advantage in the widened gauge, because the wing rail would be checking it. But only one wheelset on a vehicle can be there at any time (a length of around 10-15mm on most P4 crossings, much less than the full length of the check rail), and the other wheels will be on widened gauge. Furthermore it is not sensible to try to build a normal gauge over that short section with widened gauge each side of it -- you will be putting kinks in the rail.

*ordinary pointwork means simple turnouts. It is not a good idea to gauge-widen through K-crossings (diamonds) or where parallel-wing crossings are needed, for example in tandem turnouts. But no-one sensibly puts such complex pointwork on 40" radius curves.

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Noel » Mon Sep 19, 2016 11:52 am

Martin Wynne wrote:The factor missing from these discussions is the rail profile. Prototype BS-95R bullhead rail has a 1/2" top corner radius. Model rail sections are all over the shop in this regard. Clearly you can't calculate an incidence angle at which the flange will bind against the rail without knowing the exact profile of the flange, AND the exact profile of the rail head.


I don't disagree, and accept your point regarding the difficulties of calculation, Martin, but my comment

a radius at which the vehicle fails in some way to cope with the curve


was made in that form intentionally, since, I would suggest, binding is not the only method of failure in this context, and different rail and wheel profiles may lead to the wheelset lifting rather than binding, for example. Nevertheless, although it may be affected by rail section and wheel profile, on the face of it there should be a [probably very small] range of curvature between what is "OK" and what is definitely "not OK", depending on the wheelbase of the vehicle, which will cover all profiles.
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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Will L » Mon Sep 19, 2016 12:08 pm

Noel wrote:
Will L wrote:Wheel base = Track Curve
10 ft round a 1'3"
20 ft round a 2'6"
30 ft round a 3'9"


This is a little ambiguous, Will. I assume that the wheelbase figure is the 'real life' one, so that in model terms the figures are 1.57" (approx) and 1' 3", etc.?


Sorry yes I meant a scale model of a 10 ft wheelbase wagon (i.e. a 40mm wheel base) going round a model 1'3" curve (381mm) etc.
Will L wrote:I.e This is a none problem


If you take an extreme case, a 4-wheel vehicle with a 90mm wheelbase will not go round a 45mm radius curve. It will go round a 2000mm curve. Somewhere in between there must therefore be a radius at which the vehicle fails in some way to cope with the curve as its radius reduces. The question is at what radius does this occur without gauge widening and does it have any practical relevance? {If I have interpreted them correctly, your figures above suggest that it is potentially a problem with practical consequences.]


Sorry again, I didn't mean to imply that there was no issues getting long wheelbases round sharp curves, just that this was not a question of the wheels running out of clearance between the rails because of the angle they are running at. Reading an answer off Martin Cross's graph, which is quite handy once you've got your head round it, suggest that your 90mm model will hit the 3 degree angle of incidence on something close to a 3'0" curve. I agree that if that is what you want to do you should consider taking action because of the rail climbing potential, possibly a check rail? The point being that gauge widening will not change rail climbing issues related to the angle of incidence. The point at which the wheel will jam between the rail is a much more difficult sum, and my going in position was given that we would be well into rail climbing problems there was little point of going there?

I note Martin's comment about check rails preventing the outer wheels misbehaving, but this only moves the basic problem to the inner wheels, as there will come a point where both flanges are against the running rail and the backs of both flanges contact the check rail.


Why rubbing the back of the wheel against a check rail is less problematic than the flange against the rail face was a question I asked myself. Keith had one answer, but not one which didn't seemed that relevant to our models.

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Julian Roberts » Mon Sep 19, 2016 10:13 pm

Going back a bit Will, your post "The Final Factor" on Aug 27 835pm showed that because we can put an unprototypical amount of end float on centre axles no gauge widening is needed at all in most circumstances.

On this analysis I am unclear as to what the P4 reasoning is for any triangular gauge at all?! - rather than using anything other than a plain gauge that simply gives 18.83 regardless of curvature, at least down to what is normally regarded as a minimum, around 3' 6"?

The other thing that I don't really get
is how to use the graph that Keith posted, to work
out where you begin to have a radius that is too tight. Is it possible to show those of us less
mathematically inclined how to use the Malcolm Cross graph - perhaps taking Noel's LNER CCT
van with its long wheelbase as an example

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby grovenor-2685 » Tue Sep 20, 2016 8:28 am

If you take an extreme case, a 4-wheel vehicle with a 90mm wheelbase will not go round a 45mm radius curve. It will go round a 2000mm curve. Somewhere in between there must therefore be a radius at which the vehicle fails in some way to cope with the curve as its radius reduces.

Ok then on Malcolm's graph.
For a 4 wheel vehicle we are not concerned with the sideplay in the centre axle (V for Versine on the graph) so we only need to look at the curved lines which show the wheelbase and the radial lines giving the angle of incidence.
On Malcolm's view that 3 degrees should be the limit for good running just follow the 3 degree line till it intersects the 90mm (22'6") wheelbase line and read off the radius on the horizontal axis, near enough 2'10".
If this was a six wheel vehicle the left hand vertical axis shows that sideplay of 1.2mm would be needed, to reduce this to 1.0mm look for the intersection of the 90mm wheelbase line with the 1mm sideplay line giving a radius of about 3'3".
The required sideplay is the sum of the sideplay in the vehicle and that availble between wheels and rails so gauge widening helps by reducing the need for sideplay in the axles. The text of Malcolm's article does not suggest any of these are absolute figures. http://www.norgrove.me.uk/history_files/Mar73/Mar-73.htm
Note that the triangular gauge was the first produced by the P4 team and as we have noted has given satisfactory resullts ever since. The MkII gauge was made up with spacers and washers and would not apply any gauge widening unless you added an additional spacer when building tighter radii. I think this change was meant to reduce costs rather than for any technical reason. I found the MkII gauges harder to use and they have pretty well sat in my gage box ever since I bought them. The P4 manual goes int their use.
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Paul Townsend
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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Paul Townsend » Tue Sep 20, 2016 2:11 pm

Philip Hall wrote:
Martin Wynne wrote:

The factor missing from these discussions is the rail profile. Prototype BS-95R bullhead rail has a 1/2" top corner radius. Model rail sections are all over the shop in this regard. Clearly you can't calculate an incidence angle at which the flange will bind against the rail without knowing the exact profile of the flange, AND the exact profile of the rail head.


When the MSRG started all this they recommended the only suitable rail at the time, the Kingsway rail from Model Railway Manufacturing at Kings Cross. This rail had a distinct radius to the head, unlike our present day sections which are much squarer. This also made it look a little lighter. I still have a few odds somewhere. I also have a view that as a little more of the rail is in contact with the tyre, slightly more reliable electrical contact might ensue. One particular railway I have seen (Churston) has this rail and doesn't need to be cleaned too much.

Philip

This reminds me of my attempt a couple of years back to get a new die made for the rail extrusions as sold by all known suppliers.
I suggested to Jeremy Suter, Pete Llewellyn, EMGS then Trade Officer that they get together re this. Perhaps I should remind them at Aylesbury......
I did not get much enthusiasm as I was an apparent lone voice although I know Howard Bolton agrees with me that the current head profile is naff.

Studiolith sold the correct profile and ISTR that S4 and EMGS Stores did for a while.

When EMGS noticed flattening of the rail head...2 or more decades ago they announced it as "worn rail".

I argue the current rail head appearance is inferior as noted above by Phil and always have concerns about its effect on rolling stock track holding.

Can I invite others who would support this initiative to raise their heads? Maybe a case for crowd funding?
If anyone responds, this thread hijack topic needs its own new thread...heads up mods!

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby grovenor-2685 » Tue Sep 20, 2016 3:09 pm

Paul,
You don't need a Mod to start a new thread :)
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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Martin Wynne » Tue Sep 20, 2016 3:39 pm

Bear in mind that DCC Concepts have a new stainless steel rail section now available, and may consider a production run in nickel-silver. And Peco will shortly be introducing their version of bullhead rail in nickel-silver. It's actually a flat-bottom rail with a narrow foot the same width as the head (as they also do in 0 gauge), but it looks acceptable and will likely have the Peco advantage of being supplied dead straight.

Image

Image

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Paul Townsend » Tue Sep 20, 2016 4:02 pm

grovenor-2685 wrote:Paul,
You don't need a Mod to start a new thread :)
Regards

Yes, true but if no-one supports the idea there is no point.
Still, as Martin has suggested another way I will do the new thread so more responses there please.
Last edited by grovenor-2685 on Tue Sep 20, 2016 6:01 pm, edited 1 time in total.
Reason: Added link to new topic.

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Will L » Tue Sep 20, 2016 7:35 pm

Julian Roberts wrote:Going back a bit Will, your post "The Final Factor" on Aug 27 835pm showed that because we can put an unprototypical amount of end float on centre axles no gauge widening is needed at all in most circumstances.

On this analysis I am unclear as to what the P4 reasoning is for any triangular gauge at all?! - rather than using anything other than a plain gauge that simply gives 18.83 regardless of curvature, at least down to what is normally regarded as a minimum, around 3' 6"?

Julian

My opinion, for what it’s worth, is that nobody thought too hard about it at all. Even the 3'6" minimum is really just a bit of "is P4 really practicable" propaganda.

When Scalefour was new, the ethos of the time was that following prototype practice was the way to go. I’m pretty sure I remember that there were originally at set of gauges which implemented the prototype stepped approach. I see no sign anybody checked the maths and, as it all worked when done well, why would you?

When I was producing 00 track in the 70's roller gauges were the norm, despite the fact that it is quite hard to roll one down a bit of accurately completed track, let alone a bad bit. Once somebody shows you a three point gauge you realise it is definitely an easier tool to use, as it is much better at holding the rail in the right place while you solder it, you just needed to remember to use it the right way round on corners. As a bonus it automatically produced gauge widening which we needed, says Martin’s quote from the rule book.

Use of the society 3 point gauge produced track which most of us found worked well, assuming you had the patience to debug it and the stock you tried to run on it. We didn't get a gauge that was good for sliding round the track to check for tight spots* until the mint gauge turned up relatively recently. It was not what it was designed for but it did do the job, and you did have a point when you suggested that in this role it would be smart to make it match the 3 point gauge.
(*Adding gauge widening may be optional but tight spots are definitely a no no.)

My point is that this is an evolved situation not a planned one, developed on the basis of what the prototype did, and regardless of its true applicability to P4 models with their, in this regard, significant differences from the prototype. (I now need a soap and water mouth wash.) Then new methods were adopted when they proved their worth practically.

It is also true that the full story still isn't here. The impact on the problem of the relationship between the wheel and rail profile is still questionable, as is the implications of the steering effect of the coned wheel. I am also aware that, while I can see the rationale behind Malcolm Cross's 3 degrees limit on the angle of incidence and I'm happy it's about right, I would have thought the exact figure would vary depending on the size of the wheel as well as the flange and rail profile at Martin suggested. I haven't the foggiest idea as to how you might approach calculating the answer. I wonder if there is anything in the prototype literature on this (Keith/Martin?).

The other thing that I don't really get
is how to use the graph that Keith posted, to work
out where you begin to have a radius that is too tight. Is it possible to show those of us less
mathematically inclined how to use the Malcolm Cross graph - perhaps taking Noel's LNER CCT
van with its long wheelbase as an example


I spent a happy hour this morning working out how best to explain this, and given the graph is a bit indistinct, if it would be worth trying to reproduce it from my spreadsheet. The versine/curve radius/vehicle wheelbase falls strait out, the interesting bit is adding the angle of incidence lines and I would be more confident if I had a better understanding of the angle of incidence/wheel size issue.

Anyway Keith got there first. I can go over the thing slower and in greater detail if you like, but would it now be worth it?

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby grovenor-2685 » Tue Sep 20, 2016 7:43 pm

and given the graph is a bit indistinct,

Not so indistinct if you click on it to get the full size version! The forum software reduces it for display, and on my website the display in the text is also a reduced version. Its easier to use if printed.
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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Will L » Tue Sep 20, 2016 7:58 pm

grovenor-2685 wrote:
and given the graph is a bit indistinct,

Not so indistinct if you click on it to get the full size version! The forum software reduces it for display, and on my website the display in the text is also a reduced version. Its easier to use if printed.


Agreed that is much clearer, but it may also be different?? On the other copy the angle of incidence lines look curved, on this one they are strait.

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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby grovenor-2685 » Tue Sep 20, 2016 8:28 pm

There are two versions ad I think I have given links to both, the original was in the MRC 1967 series http://www.norgrove.me.uk/history_files/mrc3/fig3.gif and is not distinct as I could not get a better scan. The better version in the http://www.norgrove.me.uk/history_files/Mar73/Diagm.gif is from MR in 1972. I think most of the curved line effect is from the different aspect ratio although there do seem to be some small discrepancies. Back then they would have been manually drawn :)
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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Julian Roberts » Tue Sep 20, 2016 10:27 pm

Thanks Keith and Will
An LNER 2-8-2 "Cock o' the North" has 6' 2" drivers and coupled wheelbase of 19' 6" or 78mm. So looking at that graph and assuming the intermediate axles have necessary end float the minimum radius is around 2 foot 5 (if we can get the other wheels to take absurd angles.) But there's nothing about different sizes of wheels on this graph...I know I read somewhere that makes some difference.
How about a 9F? 22 foot coupled wheelbase with 5 foot wheels, if my info is correct. 2 foot 9 ins according to the graph assuming end float again. (According to Wikepedia the real thing with
thinned 2nd and 4th flanges and no centre flanges managed a minimum curve of 400 ft. That's 5 foot 3 inches on our layouts, showing what very
unprototypical things we expect from our models that we make with such attention to get every detail exactly correct!)
So all this is possible without GW given sufficient
end float...?
Thank you for your reply Will. I am not sure if you saw what I meant. What I was driving at in my question was, surely you have in setting out to show how the 31mm tool gives as much GW as we need, shown that we don't need to use it at all?
Martin's quote from the BRT3 on curves is very interesting and not only for the red box squared bit, as it also shows in general what complexities go on (e.g. different sizes of wheels). Obviously few of those issues scale down to be significant, but it seems to me that it is because of these multiple issues that we do need GW, and why it is part of the standards and generally practised. Keith mentions the Mark 2 Track Gauge. This gives far more GW than the 31mm tool, and quite a lot more than a 44 or 47mm tool, when the 0.2mm spacer is added for curves.

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Russ Elliott
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Re: Track Gauge Widening, All You’ll Ever Need to Know

Postby Russ Elliott » Wed Sep 21, 2016 12:11 pm

Martin Wynne wrote:The factor missing from these discussions is the rail profile. Prototype BS-95R bullhead rail has a 1/2" top corner radius. Model rail sections are all over the shop in this regard.

Our model wheels are also 'all over the shop'!


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