P4 vs S4 - Pro's and con's

Discuss the prototype and how to model it.
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Martin Wynne
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Re: P4 vs S4 - Pro's and con's

Postby Martin Wynne » Fri Jun 16, 2017 2:46 pm

Russ Elliott wrote:We seem to have come full circle and proved that the thing supposed to set a minimum dimension fails completely to set a minimum dimension, but in fact establishes a maximum dimension that we are not allowed to talk about.

Hi Russ,

It establishes a solid minimum when in firm contact with the gauge face of opposite rail. If it moves away from the gauge face of the opposite rail, for example if that rail is loose in the slot, the check gauge dimension increases above the minimum.

regards,

Martin.
39 years developing Templot. And counting ...

Julian Roberts
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Re: P4 vs S4 - Pro's and con's

Postby Julian Roberts » Sun Jun 18, 2017 3:36 pm

Martin Wynne wrote:
The maximum check span is given as 17.47mm (confusingly called "Between Checks" when it should self-evidently have been called "Across Checks", but it has been that way for 50 years).

This means that the minimum back-to-back is 17.47+0.1 = 17.57mm, or say 17.6mm to be practical with plastic components.

.


Hi Martin

You wrote this on 29 April.

In your complicated discussions with Russ later in this thread, which I have not been able to understand, you were talking about maximum and minimum Check Spans. Could you confirm whether your statement above still holds, with its surprising assertion that the P4 BB minimum is 17.57, surprising that is to anyone who thought 17.67 was the BB minimum? Or did the Maximum Check Span become something greater, during those conversations?

Thanks and apologies for going back such a long way in the thread.

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Martin Wynne
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Re: P4 vs S4 - Pro's and con's

Postby Martin Wynne » Sun Jun 18, 2017 4:11 pm

Julian Roberts wrote:with its surprising assertion that the P4 BB minimum is 17.57, surprising that is to anyone who thought 17.67 was the BB minimum?

Hi Julian,

The minimum back-to-back for P4 is 17.67mm, because it says so in the P4 standard: http://www.clag.org.uk/p4standards.html#table1

If you set your wheels to that, they will work fine on P4-compliant track. It has been proven over more than 40 years that the published P4 standards do work.

However, if I was building a layout using P4-compliant track, I would regard 17.57mm as the minimum back-to-back for my wheels because experience indicates that 0.1mm clearance over the maximum check span is adequate at all normal radii. (The maximum check span for P4 is given as 17.47mm -- same link).

If I had some wheels set to 17.57mm I wouldn't claim them to be complying with the P4 standard. If I wrote down or published such dimensions I would call it something else, such as P4-M.

However, I don't believe many of my wheels would actually be set to 17.57mm because in setting them I would aim to get the back-to-flange dimension close to the minimum check gauge. That's 18.15mm, so subtracting a typical production flange thickness of 0.45mm, the dimension between the wheel backs would be about 18.15 - 0.45 = 17.7mm.

In practice I'm not building a P4 layout, so the back-to-back dimension I would use on one is a bit academic. But I have been closely involved in P4 layouts in the past, so I think I'm qualified to express an opinion.

We are now on the 7th page of this topic and seem to be going round in circles. I think it would be helpful if you were to re-state what is the actual problem you are trying to solve?

regards,

Martin.
39 years developing Templot. And counting ...

Julian Roberts
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Re: P4 vs S4 - Pro's and con's

Postby Julian Roberts » Sun Jun 18, 2017 4:39 pm

I don't have any problem Martin, using a 17.67 BB tool, and I find like everyone else for the last 40 years it works very well indeed, as I said earlier with the video I put here. You have answered the question which was the only issue that I had.

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Martin Wynne
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Re: P4 vs S4 - Pro's and con's

Postby Martin Wynne » Sun Jun 18, 2017 4:58 pm

Julian Roberts wrote:I don't have any problem Martin, using a 17.67 BB tool, and I find like everyone else for the last 40 years it works very well indeed, as I said earlier with the video I put here. You have answered the question which was the only issue that I had.

Hi Julian,

That's great. Image

What it all seems to boil down to is:

1. there is a published P4 standard.

2. it works fine, and many successful layouts have been built by following it.

3. I myself would not necessarily follow it, but if so I would in no circumstances call what I was doing P4.

4. others sometimes change things too, but don't always make clear that what they are doing is not then P4.

5. the "not P4" ideas may or may not be improvements over P4, but even if the best thing since sliced bread, they are still not P4.

regards,

Martin.
39 years developing Templot. And counting ...

Julian Roberts
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Re: P4 vs S4 - Pro's and con's

Postby Julian Roberts » Mon Jun 26, 2017 2:40 pm

Here is what I've learned from this thread and indirectly a response to quite a few posts from Quentin,AM, David Thorpe, Jol. My general point is that if we use the 17.67 Back to Back tool we don't need to worry about anything and can get perfectly good running, as has been the experience of modellers for 50 years.

That hardly needs saying. So what it is really about is the difference between that and real trains, and why I at least am satisfied not to try to model to the tolerances of a real one. As I'm just an enthusiast not a professional if I've got stuff wrong then feel free to say ;) (though I may not be able to respond very quickly.)

In relation to Martin's very useful previous two posts, I have used P4 to mean the track dimensions of P4. This is a discussion (in spite of the title, which should read "Opening the Window") about the issues of venturing, either by accident or design, outside the P4 envelope for the Back to Back (BB) setting. Hopefully I clarify that issue in the text as it goes along.

P4 BB MAX MIN WINDOW.pdf
(658.55 KiB) Downloaded 44 times


As the photos are not clear on the PDF here they are again. Proper explanations in the text.

2017-06-18 11.10.15.jpg
Wheelsets real and model approaching crossing. The wheels are the same size, just drawn badly, but the model ones are meant to look closer together.

2017-06-18 11.20.42.jpg
Prototype BB window

2017-06-18 11.49.36-1.jpg
Range of BB settings

2017-06-26 06.51.08.jpg
Crossing Flangeway to scale, range of flanges.

2017-06-26 07.52.49-1.jpg
P4 range flanges drawn to scale in CF

2017-06-18 10.36.12.jpg
Running Clearances, P4 and S4

2017-06-26 06.51.21.jpg
Curved crossing essentials

Knuckles
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Re: P4 vs S4 - Pro's and con's

Postby Knuckles » Mon Jun 26, 2017 4:29 pm

Man what is this thread, Proto' Four University. :D

All this math's is making my head spin. Fun to watch how this thread progresses though, I'm just chilling with the virtual popcorn watching you all and contributing bugger all, it's always interesting what conclusions are made.

Practically I think I'll just use the gauges supplied. Seems a whole lot easier to comprehend...or maybe I'm just thick, probably the latter. :mrgreen:
“He who dares not offend cannot be honest.” Thomas Paine

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DaveHarris
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Re: P4 vs S4 - Pro's and con's

Postby DaveHarris » Tue Jun 27, 2017 3:05 pm

Must admit i agree with Knuckles latest comments. Also with Martin's comments earlier.... there are published standards which work and have worked for 40 years. I was taught ' if it works and it aint broke then dont try and fix it'. Or like Knuckles, am i missing something??? :?

QuentinD
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Re: P4 vs S4 - Pro's and con's

Postby QuentinD » Tue Jun 27, 2017 6:06 pm

I waded through the pdf but I couldn't make heads nor tails of some of the diagrams, especially whence evidence came in the color-coded ones. Insofar as I can make out, the argument boils down to 'teasing out' the implications of the track standards.

Some emphasis was placed on the idea that the 17.67mm back to back gauges were somehow going extinct. What evidence is there for this? Is not the one sold by the stores 17.67mm?

Considering that they were scarce, I would posit one further question: "Would it matter?" The 17.70 and 17.75mm gauges work admirably, and the former even accommodates the stated concern of having a workable upper envelope below the official standard. Aside from the theoretical discussion, it seems the published standard is very tolerant in practice; credit where it is due.

Quentin

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jim s-w
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Re: P4 vs S4 - Pro's and con's

Postby jim s-w » Tue Jun 27, 2017 8:53 pm

Taking inspiration from Knuckles signature line it might be worth pointing out it's as good as 7 months since this topic was started. How far along would people be if they had just got on with it by now I wonder? :D

Jim

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Horsetan
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Re: P4 vs S4 - Pro's and con's

Postby Horsetan » Fri Jun 30, 2017 10:19 am

jim s-w wrote:Taking inspiration from Knuckles signature line it might be worth pointing out it's as good as 7 months since this topic was started. How far along would people be if they had just got on with it by now I wonder? :D


Yes, but it may not be as fun as talking about it.
That would be an ecumenical matter.

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Martin Wynne
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Re: P4 vs S4 - Pro's and con's

Postby Martin Wynne » Fri Jun 30, 2017 12:10 pm

jim s-w wrote:Taking inspiration from Knuckles signature line it might be worth pointing out it's as good as 7 months since this topic was started. How far along would people be if they had just got on with it by now I wonder? :D

It's actually more than 18 months. 160 replies in 80 weeks averages 2 replies per week. I think that would leave the odd moment to build a model railway.

Martin.
39 years developing Templot. And counting ...

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Russ Elliott
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Re: P4 vs S4 - Pro's and con's

Postby Russ Elliott » Fri Jun 30, 2017 12:54 pm

I would say the debate has been chortling along for nearly 40 years, and will probably chortle along for another 40 years. It's no bad thing to check our perceptions and understandings of these things. It's probably quite healthy.

Julian Roberts
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Re: P4 vs S4 - Pro's and con's

Postby Julian Roberts » Fri Jul 07, 2017 7:50 pm

Russ summed up admirably I thought and I only have to disturb the thankfully moribund thread to say, Quentin, of course you may not have waded through all the thread to see whence my evidence came, and my little piece was assuming this prior knowledge and trying to show how I at least make sense of it - evidently unsuccessfully.... :(

For the minimum practical setting, and absolute maximum setting using a Back to Flange device, see Martin's two posts on April 29th. For the absolute maximum setting based on uncertainties of flange width and check gauge see Russ' posts May 11 @ 3.17 and May 13 @ 4.25. And yes, 17.70 gives .05 to spare and is Philip's preferred setting, he's a pro.

QuentinD
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Re: P4 vs S4 - Pro's and con's

Postby QuentinD » Sat Jul 08, 2017 6:52 am

My apologies; I misunderstood. Thank you for the references though!


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