P4 vs S4 - Pro's and con's

Discuss the prototype and how to model it.
Armchair Modeller
Posts: 1128
Joined: Thu Jan 06, 2011 7:34 pm

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

Postby Armchair Modeller » Tue Jun 06, 2017 9:37 am

Julian Roberts wrote:AM a BB gauge isn't a track gauge. It goes between the wheels ;)
Thanks for the advice chaps.


OOps! That might explain why my wheelsets always end up like this

a-U1.jpg
a-U1.jpg (14.01 KiB) Viewed 4767 times
;)

Sorry, Julian. I had walked 34 miles the previous day, not getting home until nearly 10pm. I was even less awake than normal. Similar arguments do apply to BB gauges though. I have at least two different ones and haven't measured either.

User avatar
Russ Elliott
Posts: 930
Joined: Thu Jun 02, 2011 6:38 pm

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

Postby Russ Elliott » Tue Jun 06, 2017 12:02 pm

wheel-runout.gif
wheel-runout.gif (1.85 KiB) Viewed 4750 times

User avatar
Jol Wilkinson
Posts: 777
Joined: Mon Jul 21, 2008 7:39 pm

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

Postby Jol Wilkinson » Tue Jun 06, 2017 12:14 pm

Julian,

it appears I failed to make my point.

Yes, I know a BB or B2B gauge is used between the wheels to set the back to back dimension. Weren't you asking people for the dimensions of the gauges they use? I have two different types which have the same dimensions (measured with a digital vernier gauge), two "L" shaped and one Exactoscale. Does the actual measurement matter? Not to me.

With plastic centered wheels where the wheel is retained by an interference fit on the axle it is not, in my experience, unusual for the wheel to exhibit some "wobble". This may be through manufacturing tolerances or though the wheel hub distorting as the axle is forced in. This "run out"can happen despite the care used when fitting the wheel and attempts made to minimise it. See Tom Mallard's (and other) articles on this. The wheels that seem least likely to suffer this are Ultrascale as they apparently have a smaller interference fit and benefit from pinning the wheels to the axles to avoid slip.

So, unless you can guarantee zero run out (wobble), then it is possible that the wheels will not run smoothly 100% of the time through your pointwork irrespective of which set of standards you use. It is possible to get a "mirror" run out on an axle so that the B2B is consistent on the tyres at opposite points and the axle effectively moves from side to side as the wheels rotate. In that case they probably will run through points satisfactorily, those locos we use on London Road invariably do.

So we have a set of variables that affect what we do and build. Taken to extremes you will find very variable standards used in model railways and which appear to work, most notably in OO by the RTR manufacturers. Among these variables is our own ability to effectively use what we have.

This is another reason why I believe all this navel gazing is rather pointless. Despite the apparent "inaccuracies" all this number crunching shows, the track and wheel building tools that have been used by most of us to build our models, if used carefully and consistently do produce satisfactory results. We are also constrained by commercially produced products which, as various contributors have pointed out, place potential obstacles in our paths but in reality haven't stopped many satisfactorily working layouts being produced.

My view is that better running can be achieved through "better model making" and improved commercial products, more than by agonising over the validity of established P4 standards which have been successfully used for decades.

Jol

Terry Bendall
Posts: 1632
Joined: Sun Jul 27, 2008 7:46 am

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

Postby Terry Bendall » Wed Jun 07, 2017 7:30 am

Jol Wilkinson wrote:So we have a set of variables that affect what we do and build.


Another variable is the build up of dirt on the tread of the wheel which if allowed to accumulate sufficiently can almost loose the flange. Then you have to clean the wheels either using a liquid cleaner of some sort or a glass fibre brush. Lack of care in doing this and too much pressure can introduce wobble where none previously existed. So we may have started with a wheel set that was as near accurate and without wobble as we can get it, but things may change. There is always a reason why stock falls off - all you have to do is to find the cause and locate it and sometimes this can take a long time.

In order to get wheels on their axles square these days I either press them on using the tailstock of the lathe or use a small screw press which I happen to have which was made as a machining exercise about 50 years ago. An alternative is to use a vice if the jaws are parallel. In both instances you need to find a way of dealing with the pin point on the end of the axle where that exists.

Jol Wilkinson wrote: the track and wheel building tools that have been used by most of us to build our models, if used carefully and consistently do produce satisfactory results


Quite so. Even if all the supposed inconsistencies in the dimensions and gauges were removed, a lack of care will still cause problems.

Terry Bendall

Armchair Modeller
Posts: 1128
Joined: Thu Jan 06, 2011 7:34 pm

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

Postby Armchair Modeller » Wed Jun 07, 2017 9:58 am

Actions speak louder than words? - Maybe!

Here is the video I threatened to do. The wagon is fitted with Masokits sprung axleboxes and Gibson wheels corrected for BTB with a Scalefour L shaped gauge. Weight is just 40g. Wheels are slightly dirty, but have been a lot worse and still stay on the track. Sorry for the quality of the video and for my dress sense. I do hope though that it convinces a few people that P4 can work, though no doubt there will still be doubters.



The wagon only derails on the faster attempts when it bounces back into the air after hitting the stop at the far end of the track.

Edit

The track is 1.9m long. A very rough calculation suggests that the final run was done at something between a scale equivalent of 2-300mph :?

User avatar
RobM
Posts: 940
Joined: Sun Feb 15, 2009 4:39 pm

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

Postby RobM » Wed Jun 07, 2017 4:23 pm

Richard.......:thumb

As a mediocre track, wagon and loco builder and using all the commercially available gauges I manage to get reliable running on both Manston and Woodville, OK, both are low speed running in normal conditions but the track is tested at speed and my ultimate testing is propelling wagons through the turnouts, again at speed. I have no need to go into measuring to 0.0x mm and totally rely on the gauges I have, they have stood the test of time.
http://www.robmilliken.co.uk
Updated December 2016

Knuckles
Posts: 1198
Joined: Fri Nov 18, 2011 9:15 pm

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

Postby Knuckles » Thu Jun 08, 2017 6:06 am

I like your wagon rollin' vid. Here's mine I did a year or so ago before I ended up ripping the layout up in favour of a new one. Please flick to 2:03 to ignore the bumf. It is a basic RTR wagon with minimal changes to convert to P4. I found some needed a lot of mods and others didn't. It was an easy one happy enough with just a new set of wheels yet look how it performs (performed) over my n00b trackwork.

https://youtube.com/watch?v=Nw_zxXbF_2c
“He who dares not offend cannot be honest.” Thomas Paine

http://www.shapeways.com/shops/sparksho ... eationsscc
Mostly offering Loco kits & bits in 4mm.
SCC Photon Resin Prints Price list
download/file.php?id=19320

Armchair Modeller
Posts: 1128
Joined: Thu Jan 06, 2011 7:34 pm

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

Postby Armchair Modeller » Thu Jun 08, 2017 8:38 am

I think our joint efforts pretty well prove that the existing standards and gauges work fine. We also have the confidence of knowing that anything built to those standards should run on any other layout built to P4 standards, which must be a good thing.

From my own experience of building track in other scales and gauges, I am honestly finding it easier to produce smooth running pointwork in P4 than anything else TBH. The tightness of the standards works in its favour and the gauges are so good that you don't need to worry about what the dimensions actually are. Of course, taking care in construction helps, whatever gauge and standards you use.

My take on why derailments happen are

1. Track out of gauge or alignment
2. Faults with stock - very dirty wheels, wheels out of gauge, dodgy suspension etc
3. Trying to do the impossible, like shallow fixed diamonds on a curve, or being grossly overambitious for the time and skills available.

Despite all that, we don't live on a knife edge, with paper thin margins between success and failure. P4 standards seem to me to actually be quite tolerant of minor problems, like wobbly wheels and dirt. My test wagon had almost no flange visible when I last cleaned the wheels. Up to that point it had not derailed.

I am convinced that P4 standards do work - not that I had many doubts to start with. Having worked for a long time with 2mm scale, I am used to rigid chassis with little weight and tiny flanges. The only thing that stands in the way of total reliability is my incompetence and poor workmanship - but I am working on it!
Last edited by Armchair Modeller on Thu Jun 08, 2017 8:58 am, edited 1 time in total.

Knuckles
Posts: 1198
Joined: Fri Nov 18, 2011 9:15 pm

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

Postby Knuckles » Thu Jun 08, 2017 8:47 am

Couldn't agree more. :

One thing I like about P4 (amongst other things) is the tighter clearances around points. The extra support provided for trucks is a boon and if these wagons are sprung (current favourite are Mr Bedford's units) watching them and listening to them sail through smoothly is so much more satisfying than fixed axle 00 ones bumping and rattling through.

The video above is fixed axle and so the sprung ones run even better but for wagon conversions I always work to minimum. If they are fine fixed axle then good enough, if not then mod further.

Btw, your wheelsets at top of page..... :mrgreen: Love it!
“He who dares not offend cannot be honest.” Thomas Paine

http://www.shapeways.com/shops/sparksho ... eationsscc
Mostly offering Loco kits & bits in 4mm.
SCC Photon Resin Prints Price list
download/file.php?id=19320

Armchair Modeller
Posts: 1128
Joined: Thu Jan 06, 2011 7:34 pm

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

Postby Armchair Modeller » Thu Jun 08, 2017 10:01 am

Modellers are continually trying to improve existing standards. I guess it is unavoidable.

Templot lists 6 'OO' variations (ignoring HO), O gauge has no less than 9. Even EM has 4 variants.

Sticking to one standard makes life far less confusing, even if we were a few percent off what some people consider the absolute ideal.

Julian Roberts
Posts: 749
Joined: Sat Jan 09, 2010 11:33 pm

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

Postby Julian Roberts » Sat Jun 10, 2017 10:22 pm

Tony Wilkins wrote:
If the BB had been set at 17.77mm the figures would add up and perhaps explains why using the max permitted dimension of 17.75mm gives smooth running results.
I have 4 BB gauges and they all have different measurements ranging between 17.67mm and 17.87mm which is slightly worrying. As modellers we depend on our suppliers to apply adequate quality control to achieve consistent results, so it is always worth checking that the gauges we have meet our requirements.
On the full size check rails on curved track are intended to prevent the outside wheel flange from climbing the rail not to take all the side force as it would with the P4 min BB setting.

.


My engagement with this thread arose from replying to this on P2. I showed a model train of mine (which I enjoyed making very much, thank you, Terry) running on a video absolutely fine on a 2ft radius curve propelling wagons through
pointwork. My general gist was what you are all saying more recently, P4 works just fine without worrying about things to the nearest 0.08mm

To reiterate what I said there I made several locos with fairly inaccurate BB. As they all err narrow there is no problem. One has wobbly front wheels that measure approx 17.47 but still it goes fine through pointwork.

My suggestion that a more accurate check gauge tool might be easily made arose regarding previous discussion on about P3 or 4. Where the BB is at its max of 17.75 it might be good to have a similarly exact CG tool, perhaps. At 17.75 the flangeback kisses the checkrail as the other flange is against the railhead. Above 17.75 - nose nibbling. Hot stuff. Somewhere beyond, ecstacy for the 00 cynic, derailment.

It is a perfectly valid question in view of Tony's remarks to ask what dimension a BB gauge is.

But I despair of the Forum being a place for sensible discussion when plainly people haven't bothered to read the thread, and make a travesty of some of what I said, coupled with not uninsulting suggestions as to how I should spend my time. Compared with an email from Steve Hall couteously answering my (same) question to him immediately.

QuentinD
Posts: 30
Joined: Thu Sep 01, 2016 4:41 am

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

Postby QuentinD » Sat Jun 10, 2017 11:13 pm

Forgive my slowness, but what is so special about the 17.75mm figure? In other words, what happens to a wheelset set to that back-to-back at an acute or obtuse crossing?

After all, stock set to run through S4 pointwork runs just fine through P4 (assuming it's up to snuff), and that's all the way up at 17.87-89mm. Why would this be when the standard clearly indicates a much smaller maximum for P4 track?

I get the loose impression that the 17.75 figure translates to "above this point, check function will be minimal or non-existent". In which case, 17.75 is not part of the standard but part of the diagnostic toolkit for troubleshooting. Wouldn't it make more sense to define only the minimum as part of the standard, and then put this 'functional maximum' somewhere else, away from where people might be tempted to take it seriously?

(for the record I have an Alan Gibson back to back gauge. I think it's 17.7mm but even I as a novice have found no trouble with it or any of the critical dimensions.)

It seems that the mathematical precision of the discussion goes beyond the precision we can achieve easily in our own homes, though miraculously things seem to work in spite of this!

Quentin
Last edited by QuentinD on Sat Jun 10, 2017 11:24 pm, edited 2 times in total.

Philip Hall
Posts: 1267
Joined: Mon Aug 10, 2009 7:49 pm

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

Postby Philip Hall » Sat Jun 10, 2017 11:16 pm

I think that some of this discussion over precise measurements has eventually highlighted a problem that might be perceived with the mounting of wheels upon axles. Precise measurements and the variations/tolerances in the P4 standards render such precision in checking or adjusting gauges unnecessary; however, wheelsets that fall outside of those figures can fail through pointwork in certain circumstances. I came to the conclusion long ago that I have spoken of in these pages many times, and that is (forgive me for saying it again) that a wheelset assembled with its back to back setting 'bang on' WILL eventually move from dead true to wobble.

Jol has made the correct point that assembly of wheelsets as accurately as possible in the first place is the best we can do. No amount of tinkering with back to back dimensions is going to change the fact that the back to back setting is going to move over time, and (as a gentleman by the name of W.E.Ward-Platt wrote in the October 1965 Railway Modeller) "if one's track cannot accommodate this sort of thing one will never get reliable running". That article should be required reading for anyone who aspires to a big reliable railway, but I digress.

I might add that my experience is that Alan Gibson wheels can wobble when put on the axles, but that wobble is usually the tyre moving on the centre, not the centre wobbling. Gently squeezing tyres onto centres with fine pliers between the spokes often sorts out things, but if it doesn't a bit of gentle bending helps. Increasingly I am fitting paper or plastic shims to the GW wheel press to support the tyre as the wheel is pressed on. I also put the press in a very big vice (the jaws of which do not wobble) and press in the axles gently. Gently because a big vice is quite capable of wrecking the GW press which is made from aluminium. A nicely chamfered axle end is also essential. Sharman wheels do not need the shim support to the tyre because the tyres are locked onto the centres by moulding rather than just pressed on as with AG. Both Sharman and AG wheels deform slightly as the axle goes in; indeed Sharmans seemed to 'shrink down' on the axle to a tight fit as time passed.

Ultrascale are a slightly different animal in that the plastic is somewhat harder than AG or Sharman, and the centre hole to axle interface is more tightly controlled. A large chamfer is not needed (although a small one is) as the centre hole does not deform as the axle goes in, and no wobble should occur from tyres moving, as they are locked on by the centres being moulded into the tyre as with Sharmans. They seem to go on best if just pushed onto the axle with a rotating motion, but I often still use the GW press although David Rogers does not recommend its use. Here I do use shims to support the wheel as it is more rigid and thus possibly more prone to deforming with the pressures of the press. Many folk pin Ultrascale wheels to axles, and I used to, but now I use a method mentioned by Chris Pendlenton in MRJ a few years ago; I turn a very shallow groove in the axle about 1mm in from the end, and also lightly abrade the axle with a file. A drop of Loctite 601 or 603 goes in the end of the axle hole and the groove both retains the Loctite and stops it going further down the axle to the wheel press pins with the subsequent grief that can ensue.

Knuckles mentions Markits wheels, and yes, it would be nice to have P4 versions as they are strong and easy to use, but given the minority nature of us P4 adherents I think we will be chasing rainbows to imagine they will ever happen.

Philip

User avatar
Martin Wynne
Posts: 818
Joined: Mon May 14, 2012 4:27 pm

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

Postby Martin Wynne » Sat Jun 10, 2017 11:29 pm

QuentinD wrote:Wouldn't it make more sense to define only the minimum as part of the standard

Agree. At last someone talks sense.

The back-to-back dimension is a MINIMUM, determined only by the need to have a working clearance over the maximum check span.

The MAXIMUM spacing of the wheels on an axle is determined by the flange thickness, such that the back-to-opposite-flange dimension does not exceed the minimum check gauge.

Virtually this entire topic could have been avoided if the published standards did not include double-dimensioning, specifying both maximum and minimum for dimensions where only one of those is needed or relevant.

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

User avatar
Jol Wilkinson
Posts: 777
Joined: Mon Jul 21, 2008 7:39 pm

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

Postby Jol Wilkinson » Sun Jun 11, 2017 8:09 am

Julian Roberts wrote:
Tony Wilkins wrote:
If the BB had been set at 17.77mm the figures would add up and perhaps explains why using the max permitted dimension of 17.75mm gives smooth running results.
I have 4 BB gauges and they all have different measurements ranging between 17.67mm and 17.87mm which is slightly worrying. As modellers we depend on our suppliers to apply adequate quality control to achieve consistent results, so it is always worth checking that the gauges we have meet our requirements.
On the full size check rails on curved track are intended to prevent the outside wheel flange from climbing the rail not to take all the side force as it would with the P4 min BB setting.

.


My engagement with this thread arose from replying to this on P2. I showed a model train of mine (which I enjoyed making very much, thank you, Terry) running on a video absolutely fine on a 2ft radius curve propelling wagons through
pointwork. My general gist was what you are all saying more recently, P4 works just fine without worrying about things to the nearest 0.08mm

To reiterate what I said there I made several locos with fairly inaccurate BB. As they all err narrow there is no problem. One has wobbly front wheels that measure approx 17.47 but still it goes fine through pointwork.

My suggestion that a more accurate check gauge tool might be easily made arose regarding previous discussion on about P3 or 4. Where the BB is at its max of 17.75 it might be good to have a similarly exact CG tool, perhaps. At 17.75 the flangeback kisses the checkrail as the other flange is against the railhead. Above 17.75 - nose nibbling. Hot stuff. Somewhere beyond, ecstacy for the 00 cynic, derailment.

It is a perfectly valid question in view of Tony's remarks to ask what dimension a BB gauge is.

But I despair of the Forum being a place for sensible discussion when plainly people haven't bothered to read the thread, and make a travesty of some of what I said, coupled with not uninsulting suggestions as to how I should spend my time. Compared with an email from Steve Hall couteously answering my (same) question to him immediately.


Julian,

I regret that you feel that this Forum is apparently mot a place for sensible discussion. Six pages and 139 posts, discussing/debating wheel and track dimensions would, I think, suggest otherwise. Having followed the topic, but not partaken in the mathematical debate. I became rather frustrated that this didn't seem to be getting anywhere, although Quentin and Martin now seem to have suggested what may be a pragmatic solution.

My frustration was brought about by this concentration on very small variations in "standard" measurements, when other factors can have an impact greater than the variance being discussed. That is why I raised the question of construction "variables" which will invariably exceed the established track and wheel standards and which, in my view, would provide a greater practical gain if they could be reduced. Redefining track standards and manufacturing different/more accurate gauges (which is what I think you suggested at one point) doesn't address the difficulties we have with wheel sets if they are less than totally accurately set up. We are in the hands of commercial suppliers for nearly all of the products we use (I exclude the Society's stores from that categorisation) and must make the best of what is available. For me, wheels, especially larger diameter loco wheels represent the biggest challenge in achieving "error free" running when building a model. .001" variation at the hub axle mounting on a 6 'loco wheel becomes .008" at the rim. That is .02mm (if I have my maths correct). B2B changes during running, especially with carriage and wagon wheels, is another. How often do you read that, when a vehicle derails, then the B2B is the first thing to check.

It was also suggested that the commonly available B/H track varied in manufacturing tolerances, which could possibly have an impact. However, as the track dimensions we work to are inside, rather than outside, that doesn't seem to present an issue.

What this topic has done, for me at least, is to again highlight the need for more accurate and consistent wheelset assembly. The range of Exactoscale carriage and wagon wheels have largely addressed that for rolling stock, but steam loco wheels can still present a problem (I have no experience with diesel and electric prototype models). The Exactoscale and Ultrascale ranges don't supply what I need and with the demise of Sharman Wheels that only leaves AGW. I don't share Philip's view that the problems with AG wheels (or any other plastic centred wheel) are solely due to the tyre/centre relationship. Whenever you distort a plastic centre, particularly a non uniform one (i.e. one with a crankpin hub) by forcing in an axle to get an interference fit, then some distortion is possible.

If I could get totally true running wheels, 100% of the time, then I could worry about whether or not established P4 standards need redefining.

Jol

Armchair Modeller
Posts: 1128
Joined: Thu Jan 06, 2011 7:34 pm

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

Postby Armchair Modeller » Sun Jun 11, 2017 10:39 am

Having assembled a number of wheelsets recently, I agree wholeheartedly that careful assembly of wheels does make a difference.

A slight chamfer on the axle ends.
Gently rotating a circular file in the axle hole to get rid of any plastic flash on the inner edge.
Use of a GW wheelpress, with shims around any protruding centre boss. Thin card seems to work well.
Using a BTB gauge in the final push to make sure that the BTB measurement is OK - I find you can't rely on the stops on the GW press, as the axle length varies slightly from one axle to another on Gibsons.

With the Gibson wheels, I have been gently squeezing the GW press by hand, rather than using a vice. That seems to work fine for me.

The idea of using shims to keep the wheels square in the wheel press was a big plus, I think. I would never have thought of that one on my own!

Philip Hall
Posts: 1267
Joined: Mon Aug 10, 2009 7:49 pm

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

Postby Philip Hall » Sun Jun 11, 2017 1:29 pm

Perhaps I should have said that many times I feel that the tyre on an AG wheel can move, but not always, and I agree with Jol that distortion of the wheel is possible, maybe even likely, as the axle goes in. I did have recently a set of wheels which were perfectly concentric but were a very stiff fit on the axles, which is how I came to use a vice - it was the only way to get enough pressure. They went on perfectly first time and almost dead true, and the concentricity was maintained!

As a matter of course now I always mount a wheel on a long axle running in a bearing in the tailstock of the lathe (which saves having to prepare a mandrel) to check for concentricity, and I have a feeling that having mounted the wheel once in this way the axle is eased as it goes into the wheel upon final fitting. However, once is enough otherwise a loose fitting wheel could result.

Philip

Julian Roberts
Posts: 749
Joined: Sat Jan 09, 2010 11:33 pm

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

Postby Julian Roberts » Mon Jun 12, 2017 5:14 pm

Jol
Your answers to my brief question, what is runout (which I had meant to previously ask Russ and his diagram provides similar clarity), have provided much enlightenment, so thank you very much.

To jump to your last sentence my aim has been to understand the standards, rather than redefine them. The way I see it now, the issue is how to work pragmatically within the standards. However I am writing a separate piece about that and for now just want to mention one thing.

You say

.001" variation at the hub axle mounting on a 6 'loco wheel becomes .008" at the rim. That is .02mm (if I have my maths correct). 




However according to my calculator it is 0.2 not 0.02. All I infer from that is, surely for a 17.75 max that wheel needs a 17.55 min, much the same as I have (accidentally) used on my earlier locos, don't you think? But following Martin's reasoning and allowing ourselves an absolute minimum of a sensible clearance over the Check Span, this becomes simple. Isn't good modelling also about knowing when and how to break the rules?

User avatar
Jol Wilkinson
Posts: 777
Joined: Mon Jul 21, 2008 7:39 pm

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

Postby Jol Wilkinson » Mon Jun 12, 2017 6:45 pm

Julian,

well spotted but not surprising with your ability with numbers.

Rather than breaking the rules, I would rather find a way to assemble my models with techniques and components that don't require me to do so. Once you start breaking the rules and finding justification for so doing, then where would it lead?

Jol

Armchair Modeller
Posts: 1128
Joined: Thu Jan 06, 2011 7:34 pm

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

Postby Armchair Modeller » Mon Jun 12, 2017 7:06 pm

I assumed that the 0.001" figure was pulled out of the air to show how a seemingly small deviation at the wheel hub resulted in a much larger deviation at the wheel rim. I doubt it was implied that a 0.2mm wobble at the rim is what we we should actually expect to see on our models as a matter of course. Hopefully, it would be much smaller than that.

In any case, wheels of different radii would give different results. The equivalent figure for 'Cornwall' with its 8ft 6in drivers would be 0.28mm, whilst small industrial tank locos would be more like 0.1mm - if my maths is any good.

As for breaking rules, the specifications are surely guidelines as far as us modellers are concerned. We are all free to do things differently if we wish.

User avatar
Russ Elliott
Posts: 930
Joined: Thu Jun 02, 2011 6:38 pm

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

Postby Russ Elliott » Wed Jun 14, 2017 12:06 pm

Julian Roberts wrote:Scruffy drawing attached.
download/file.php?id=14262&t=1

How does that set a minimum?

Julian Roberts
Posts: 749
Joined: Sat Jan 09, 2010 11:33 pm

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

Postby Julian Roberts » Wed Jun 14, 2017 10:01 pm

Russ I hope you won't mind me saying I don't really want to go into that issue again in public as it has upset so many people, as it is only an issue if we choose to make it one. Also it was a question, might it give more accuracy? (if we want to be ultra and unecessarily fussy).

But not to dodge your question here goes...

I put on a later post that Martin had said earlier that a reasonable cost tool would have a minimum accuracy of 1 thou" = 0.0254mm. So if that's only in the plus direction as we can't have a minimum less than 18.15 does it follow we may get up to 18.18? But varying thickness of nominally P4
compliant rail wouldn't affect the accuracy of this tool any further, surely? So the minimum would be a range of 18.15-8

Again can I stress to anyone else I am personally not interested in trying to work at the level of accuracy where this would be critical, as I know my skill in hitting the BB is unlikely to be much better than the nearest 0.05mm.
Last edited by Julian Roberts on Wed Jun 14, 2017 10:43 pm, edited 1 time in total.

User avatar
Martin Wynne
Posts: 818
Joined: Mon May 14, 2012 4:27 pm

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

Postby Martin Wynne » Wed Jun 14, 2017 10:43 pm

Julian Roberts wrote:So if that's only in the plus direction as we can't have a minimum less than 18.15 does it follow we may get up to 18.18?

Hi Julian,

As I mentioned earlier, the manufacturing tolerance on a gauge tool is not the same as the tolerances in the track standard. To be called a "gauge" tool you would expect a chunk of metal to be manufactured to that degree of tolerance, so yes if you measure the gauge tool it should be within the range 18.15mm - 18.18mm, or ideally better.

But you can't hope to build track out of wood and plastic to that level of tolerance. All you can say is that the check rail must not be less than 18.15mm from the opposite rail. It can be further away than that, but limited by the maximum check span dimension.

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

User avatar
Russ Elliott
Posts: 930
Joined: Thu Jun 02, 2011 6:38 pm

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

Postby Russ Elliott » Thu Jun 15, 2017 10:39 am

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.

Julian Roberts
Posts: 749
Joined: Sat Jan 09, 2010 11:33 pm

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

Postby Julian Roberts » Fri Jun 16, 2017 2:29 pm

Surely anyone is allowed to talk about anything? - except, if I do, it seems to upset everyone!


Return to “Track and Turnouts”

Who is online

Users browsing this forum: No registered users and 5 guests