Re: Track and Wheel Standards

Discuss the prototype and how to model it.
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grovenor-2685
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Re: Track and wheel standards

Postby grovenor-2685 » Sat May 06, 2017 8:02 pm

grovenor-2685 wrote:As well as being out of place in a discussion on vehicle suspension the discussion above does raise some issues with the standards that perhaps need a bit more exploration. i will come back to it after a bit of preparation.
Regards

i wrote this after reading a post from Tony Wilkins that I thought was on here, however, I find it is actually on the P4 v S4 topic.
The relevant sentence was this:
I feel I should point out that there is actually an error with the P4 standards which has been there from day one. In the published standards the quoted figure for the Check Gauge (BB plus EF) is 18.15mm Since the min BB is 17.67mm and the EF is 0.38mm this adds up to 18.05mm not 18.15mm. This means that for a wheelset with 17.67mm BB at a check rail the flange of the opposite wheel wiil not be in contact with the running rail but 0.1mm away from it. This may not seem important, but if the wheelset is running through a crossing with the flange in contact with the stock rail, the back of the opposite wheel flange will strike the knuckle of the crossing as it overlaps it by that 0.1mm difference assuming that the track gauge is the nominal value.

This caused me to look at the standards as I had thought that the set of equations used to validate the figures was complete. Examination revealed that the condition given by Tony does NOT in fact get checked by any of the equations and an additional equation is needed. This would be:
(BBmin + EFmin) - (TGmin - CF min) >/= 0. This is effectively the converse to equation 2.
Putting the figures to these shows that it is required to eliminate the wide tolerances that the P4 standards give to BB, EF and CF to allow both this new equation and equation 2 to be satisfied.
See attached calculations.
P4 stds.xls
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P4 stds.ods
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The reason this does not give significant trouble in practice is that the problem will only occur when the wheelset is running up against the stockrail, ie on the larger radius of a curved turnout where the crossing is on the inside rail of the curve. Also if using CF gauges correctly CFmin should never be encountered.
Regards

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Martin Wynne
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Re: Track and Wheel Standards

Postby Martin Wynne » Sat May 06, 2017 11:39 pm

This also happens on the prototype if the stock rail is side-cut worn or the flange is worn thinner. This is the reason for the flare angle on the end of the wing rail, and the knuckle radius.

This also means that gauge-widening has no effect over the length of the wing rail. But that will usually apply to only one wheelset at a time.

It is the reason for setting the wheels as close as possible to the maximum back-to-flange dimension (without ever exceeding it). With one wheel running with the flange against the rail head, the other wheel should just kiss the check rail. Throw away your back-to-back gauges and use a wheel setting fixture, such as described at: http://4-sf.uk

Martin.
40 years developing Templot. And counting ...

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Russ Elliott
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Re: Track and wheel standards

Postby Russ Elliott » Sun May 07, 2017 1:39 am

Yes, the MRSG table given in the January 67 MRC was faulty. The standards published by the Scalefour Society however did not repeat the error, i.e. the Society version never needed to state where 18.15mm was derived from because it never stated a value for 'BB + EF'.

grovenor-2685 wrote:This caused me to look at the standards as I had thought that the set of equations used to validate the figures was complete. Examination revealed that the condition given by Tony does NOT in fact get checked by any of the equations and an additional equation is needed. This would be: (BBmin + EFmin) - (TGmin - CF min) >/= 0. This is effectively the converse to equation 2.

I proposed exactly the same condition to the Technical Subcommittee at its meeting on November 1986, when we were putting the Society Digest (issue 2) to bed, but it was not adopted, not so much because of any disagreement on the principle of such a new running condition, but because of the political embarrassment that would arise from the fact that the P4 standards could not comply with it.

p4stan-09-converse-condition2.gif
p4stan-09-converse-condition2.gif (3.18 KiB) Viewed 2887 times

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Brian Harrap
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Re: Track and Wheel Standards

Postby Brian Harrap » Thu May 11, 2017 4:52 pm

Dunno how I ever get anything to run. B

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Flymo748
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Re: Track and Wheel Standards

Postby Flymo748 » Thu May 11, 2017 7:09 pm

Brian Harrap wrote:Dunno how I ever get anything to run. B


Those of us who have seen you, and your splendid layouts, in action would suggest it is an arcane combination of mystical incantations, sacrificed goats and a gurt big file...

Cheers
Flymo
Beware of Trains - occasional modelling in progress!
www.5522models.co.uk

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Brian Harrap
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Re: Track and Wheel Standards

Postby Brian Harrap » Mon May 15, 2017 10:34 pm

Flymo748 wrote:
Brian Harrap wrote:Dunno how I ever get anything to run. B


Those of us who have seen you, and your splendid layouts, in action would suggest it is an arcane combination of mystical incantations, sacrificed goats and a gurt big file...

Cheers
Flymo

................and a sprinkling of fairy dust. B

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Re6/6
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Re: Track and Wheel Standards

Postby Re6/6 » Tue May 16, 2017 12:16 pm

Flymo748 wrote:
Brian Harrap wrote:Dunno how I ever get anything to run. B


Those of us who have seen you, and your splendid layouts, in action would suggest it is an arcane combination of mystical incantations, sacrificed goats and a gurt big file...

Cheers
Flymo


Wait until you see the new one Paul. I've been privileged to have had the smallest glimpse of some of it! :shock:

He probably won't thank me for posting this bit of ongoing work! ;)

099a.jpg
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John

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Russ Elliott
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Re: Track and Wheel Standards

Postby Russ Elliott » Wed Jun 14, 2017 10:07 am

Keith - I've taken the opportunity of re-styling your useful spreadsheet, and making any clearance violations automatically appear in red. (I would have sent it to you via PM, but attachments aren't allowed in the PM system.)

P4 stds.xls
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Julian Roberts
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Re: Track and Wheel Standards: Prototype Questions

Postby Julian Roberts » Wed Dec 06, 2017 10:47 am

I heard recently from a member of this Society that on the prototype flanges wear from 29 mm to 22mm thick before reprofiling. That scales to 0.38 to 0.28mm and puts Roger Sanders article in the latest Snoozein a very different light.

Back to Back on the prototype seems to be variable too.

As check rails wear surely there must be a tolerance on the check gauge between new and needing replacement? Our information seems pretty much non existent.

Understanding our scaled down issues might be assisted by a deeper understanding of the real thing surely? But is some enlightenment from our experts possible without being referred to hundreds of pages of incomprehensible numbers?!

Alan Turner
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Re: Track and Wheel Standards

Postby Alan Turner » Thu Dec 07, 2017 10:43 am

Back to Back dimension for Steam Locomotive wheels is: 1360 to 1362 mm. i.e. 2mm which is .025mm or .001" in P4.

Flange wear toleration depends on the tread profile but is generally 4 to 5 mm (Euro Star seems to be an exception). which is .05 mm or .002" in P4.

Are you suggesting that these tolerances are in any way significant to us modellers?

regards

Alan

Julian Roberts
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Re: Track and Wheel Standards

Postby Julian Roberts » Fri Dec 08, 2017 9:13 am

Thanks Alan. Not really suggesting anything, more asking. The numbers I had been given may have referred to Voyager trains. I'm not sure if you imply they may be correct for Eurostar too, even if not generally correct. My point being really that if the real thing can have an extra 7mm slop each side from wear, 0.1 in our terms, and if that is on very high speed trains, Roger Sanders' argument that it is the slop in P4 that causes running problems would seem not quite confirmed in reference to the prototype. But I'm the amateur here asking for information from you guys that know.

You don't mention the Check Gauge. But anyway thanks.

PS Obviously the prototype scaled down (S4) has wider BB than P4. But if it had 0.28 flanges there would be quite a bit more slop than it does now. Haven't got time to do the maths now to work out how much, maybe getting towards P4 minimum slop with 17.75 max BB...


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