What back to back setting do you use?

[Philip Hall]

I have a variety of rail profiles here for the new layout, most look about the same but there are variations. The rail originally propounded as suitable for P4 standards in the original MRC articles was Kingsway, from the Model Railway Manufacturing Co in Kings Cross, and this had quite a rounded head to the rail, and also looked quite light. I think it might have been sold as Code 65, whereas our present rail is Code 75. I still have some Kingsway somewhere.

I have recently acquired some original Studiolith rail and this doesn’t look a lot different to present day Code 75, although the head is a little different. But the radius to the head does not strike me as the same as the rounded head of Kingsway. This difference in head profile can make a difference to the running clearances as Martin as said.

Philip

[Paul Townsend]

And I have been moaning for years that the die used to extrude NS rail is worn out.
The head cross-section and hence the gauge corner are much flatter than in Studiolith days.
This applies to rail from Jeremy, EMGS stores and C&L, presumably all from the same factory.

I informed all 3 suppliers years ago, got a polite acceptance but no undertaking to commission a new die.

The difference is offensive to the eye looking along track as the modern stuff looks much wider.
In light of recent contributions to this thread it may well affect running reliability too.

Having been a LibDem campaigner for 30+ years I am used to crying in the wilderness but I just hope rail buyers will see the light soonish before my clogs wear out.

Howard Bolton solved this by cornering the last known stock of Studiolith rail....clever B^&%$r

Edit...
Ouch, Philip beat me to it by 10minutes!

[Philip Hall]

I was lucky with the Studiolith rail - I had no idea it was Studiolith, I just swapped it for steel I didn't want and a kind friend offered it to me. He is a firm believer in steel. No, we're not going there again...

But having briefly looked at the profile, it does look better than some of the modern stuff but not as slim and rounded as my memory of Kingsway. I am trying to locate a few inches of it and will report further if I find it.

Philip

[Paul Townsend]

Tomorrow is the next meet of BS4 ( Bristol AG) and I have circulated a suggestion that we all bring our gauges and measurers.

Of course I am only a humble Group Member. Really Tim Venton should be issuing this as an edict for BS4......watch this space.

We met, we saw each others, and we measured, ( Veni, Vidi, Measurii ? sorry a bit rusty here ).
Even without an edict from Tim, who claims he forgot, half a dozen members brought samples. We reckon he chickened out but he will show us a Sissons gauge soon, so may get forgiven.

I haven't recorded results but the selection included 2 early S4 Stores Blue Ls, 2 Exactoscale monsters...one of each type...Hi and Lo end of spec, one DCC croquet mallet, one GW set to hi end. Some of us have original Studiolith Ls but weren't to hand at short notice.

None were out of spec and all except the Lo end Exactoscale were up in the top of range so should be good.

Mark pointed out that the types with large flat surfaces (Exactoscale and GW Models) usually taper a bit. Checks confirmed this but only a few x .01mm so unlikely to be a big problem.

I commend the exercise to other AGs.

[Tony Wilkins]

Hi Paul.
The Nottingham Area Group are planning to have a gauge measuring session early in January as we don't have a meeting now until the new year. By then this topic may well be old hat, but if anything of interest turns up, I will post it here. There will no doubt be a results summary under the NAG area group reports as well. I of course am one of the renegades as I personally work to S4 standards and have acquired several BB gauges ranging from 17.67 to 17.87mm!
By the way, I concur re the degenerating Bullhead rail profile over the years, what we have now is very different to what it used to be. Like Martin, I too have had one batch of rail that had a sharp burr on one edge of the rail head that needed gently removing before using.
Regards
Tony.

[Julian Roberts]

I am sure every little helps as (groan) the advert says, and don't want to discourage Tim in his search for successful running, but everyone in this latest discussion here seems to take Roger Sanders article as if it is Holy Writ. Well I don't! - for the following reasons:

1. He makes no reference to the Check Gauge. Any wider than 17.75 is beginning to ask for problems at common crossings, in P4.

2. The problem of vehicle or bogie hunting used to occur (and sometimes still does) as speed increases, say above 50mph, not at typical P4 model scale 30ish speeds.

3. Real flanges are allowed to wear down from 29 to 22mm on some trains, possibly the Virgin or XCountry Voyagers. Equates to 0.38 to 0.28mm in our scale. That's double the allowance we make for our flanges production tolerance, meaning we could even in S4 have a full 0.1mm reduction in BB yet have prototypical slop. I tried to raise this as a discussion on the Track and Wheel Standards thread but without success. Yes it's not as much slop as in P4 but seems to me to at least put a question mark against Roger's general point that it is the excessive slop that causes our derailments.

4. If reducing the slop is so vital the commonly undergauge C&L track measuring c.18.65 - 75 should be just perfect.

I suggest that it's John Anderson's article that contains ideas of equal or greater relevance to getting good running, and rather than poring over microscopic differences of wheel BB settings and gauges, a lot more could be learnt from making an axle weight measuring device as per his article, and seeing if there's a connection between lightly loaded axles and derailments. However I have found even a half mm height difference significantly affects a spring's force so it's vital the little piece of track for the axle concerned is EXACTLY the same height as the rest.

[Le Corbusier]

At the risk of putting my head above the parapet and talking about what I fully accept I may not completely understand, I would make the following observations.

In my case I had a specific issue with my track and by setting the B to B as suggested by Roger and (in the digest notes) towards the upper end of the recommended dims (in my case 17.62-3)it would appear that I now have good running at the moment

I did not think anyone was suggesting setting the B to B wider than 17.75 unless the track was laid to S4 standards?

I understood that even at the max of 17.75 there was still an allowance for tolerance ... ie the between checks dim is set at 17.47 giving 0.68 flange way compared to an effective flange of max 0.4 ?

My reading of Roger's article led me to believe that historically the range of 17.67 - 17.75 with 17.67 being the original check gauge dimension was set to accommodate the potential for tight radius curves? I thought his contention was that the bracketing had been set over wide and for good running the nearer to the higher figure the better. In my case my original 'L' gauge (I think bought from the EMGS but not certain) when measured was coming in with a variation between 17.6 to 17.55 which was way off.

On the subject of weight and weight distribution I am far too inexperienced to be able to comment in a meaningful way on the detail.

It seems to me that having a sufficiency of weight is necessary to ensure good track holding as speeds increase (particularly where changes in direction are concerned) ... whether adapting the weight distribution from an even distribution like on the prototype to an eccentric one for models is beneficial I really couldn't comment (though wouldn't that play merry hell with CSBs) ... but surely the vehicle should run smoothly on its own with minimal weight when at slower speeds if the wheel alignments, back to backs and track construction are all correct? Additional weighting might overcome shortcomings and eccentric loading might further aid the track holding, but in a sense it suggests to me that if such measures are essential at slower speeds, then they are working as a remedial and covering up a fault that really should be corrected first?

Happy to be told otherwise though

[Noel]

3. Real flanges are allowed to wear down from 29 to 22mm on some trains, possibly the Virgin or XCountry Voyagers. Equates to 0.38 to 0.28mm in our scale.

Linear dimensions can be scaled, but the mass of a model may have no relationship at all to the mass of the real thing, and if it does it's probably subject to an inverse cube law, so the forces imposed by and on a model do not have a linear relationship with those imposed on and by the prototype [Gravity and Time can't be scaled at all], so what the prototype does is not necessarily a reliable guide to what we can do.

but surely the vehicle should run smoothly on its own with minimal weight when at slower speeds if the wheel alignments, back to backs and track construction are all correct?

Possibly true in theory, for single vehicles. However, we don't generally deal with single vehicles, but with the complex interactions between a collection of probably loosely coupled [which would include most automatic couplings] vehicles on probably less than 100% perfect track. There may be damping from sprung buffers, there may be different spring/compensation methods in use, with or without damping, there may be differences in weight and axle loading between vehicles, there will be at least some variation in b-to-b between wheelsets, and there is some evidence that some methods of compensation are affected by whether the compensated axle is leading or trailing. The dynamics of that little lot are likely to be horribly complex, even if the operator gets everything right.

[Le Corbusier]

but surely the vehicle should run smoothly on its own with minimal weight when at slower speeds if the wheel alignments, back to backs and track construction are all correct?

Possibly true in theory, for single vehicles. However, we don't generally deal with single vehicles, but with the complex interactions between a collection of probably loosely coupled [which would include most automatic couplings] vehicles on probably less than 100% perfect track. There may be damping from sprung buffers, there may be different spring/compensation methods in use, with or without damping, there may be differences in weight and axle loading between vehicles, there will be at least some variation in b-to-b between wheel sets, and there is some evidence that some methods of compensation are affected by whether the compensated axle is leading or trailing. The dynamics of that little lot are likely to be horribly complex, even if the operator gets everything right.

Noel,

I think what I was trying to suggest was that this should be the start point with each individual piece of rolling stock and if derailment is occurring at this stage then it should be dealt with by either adjustments to the track or the vehicle.

I had assumed that the purpose of weighting the stock was to try and iron out the dynamics once multiple pieces of stock become involved coupled to varying speeds.

I was not trying to suggest that Julian's points were invalid in anyway.

[Noel]

I think what I was trying to suggest was that this should be the start point with each individual piece of rolling stock and if derailment is occurring at this stage then it should be dealt with by either adjustments to the track or the vehicle.

No disagreement with you there, I was just making the point that the behaviour of a single vehicle in isolation is not necessarily the end of the story. Basically, if one vehicle misbehaves it's probably the vehicle, if several do it's probably the track, but it could, of course, be both vehicles and track. Likewise, if the problem is in one location, it's probably the track at that point, but if several locations, then it may be vehicles, or both vehicles and track.

[Julian Roberts]

Tim

First please rest assured I don't disagree with any of your BB conclusions. If it works better hallelujah.

I like you have been looking for the ways to get utter reliability of running.

However I start from the point that one of the things I like about trains is that they are big. Big boys toys. Really big! And very very heavy. Very very very very heavy. And that's why they behave as they do! A huge amount of power is required to break the inertia of all that weight. And it's the power kick that thrills...isn't it!? So trains start and stop with great difficulty. But roll along effortlessly. The magic of steel wheel on steel rail. That's the big thrill about trains for me. And the fact that this effortless movement is why they are so vital in saving transportation energy where big traffic flows are concerned (though disappointingly the energy required increases with very high speed.)

Anyway, a 50 ton wagon on 4 wheels...as against a road vehicle that weight with...12 wheels, some of them double wheels?...

Surely it's this weight that keeps the wheel on the rail and thus necessitates just an approx 1 inch flange in combo with its conicity? If it was as light as a road vehicle on each wheel surely a fundamental rethink would be needed?

So I can't see the contemporary attraction of making models light. Certainly brass is a much better material for lovely detail modelling than white metal but the loss of the latter's weight seems to me a downside and I try to mitigate the lack of it. The diminutive High Level Barclay Tank (my last creation) I stuffed with lead to weigh as much as I possibly could; around 250g I think.

The limit on wagon weight is what lead you can attach without it being visible in the case of open wagons. A flat wagon is the most difficult as lead can only be put underneath to the loss of some detail but hopefully not obvious except to the most prying eyes. So a maximum attainable is about 50g. An empty mineral wagon can have the floor covered in a layer of lead flashing without anyone noticing (except P4 sleuths! ) so that's much easier.

So I can't really see any reason to try to get good running without 50g minimum weight for each wagon and the fact it will immediately hold the rails much better seems to me to make it a no brainer. Propelling vehicles is an essential requirement for shunting at Monsaldale surely? - much more hazardous without good weight.

The upper weight limit is that a train must have fairly equal weight or lighter vehicles could fall over on curves.

Then with locos it's obvious that the more they weigh the more they can pull AND the more they will stick down on the rails. Again a win win no brainer but some odd delicacy seems to have taken hold of the fraternity rather like "nouveau cuisine" where you get delicious food but are left desperate in an Oliver situation 'can I have more'! - an exquisite model as light as a feather or piece of jewellery. That's not like the real thing. The real thing is hard brutish dirty dangerous unforgiving and utterly lethal in the wrong hands!

So that's my reaction to your suggestion the model should behave well without added weight. Please don't be offended! I just got a bit carried away that's all (its been a long day and not over yet...Glasgow to Eastbourne and back! - with a catering crew strike on Virgin trains!!). Your thread is great (not keeping up with it all) and your learning process interesting to all; responding helps me define my own dormant attitudes. Most of us are just amateurs tho the pros keep us on the straight and narrow. Best of all when they disagree with each other!!

As for the track issues the critical thing about the check gauge is when a vehicle goes through a diverging route, IF the flange is hard up against the outer rail OF THE CURVE (I. E. the closure rail and crossing V, not the stock rail) because of its tangential or centrifugal force, the check rail prevents the guiding flange from hitting the crossing V. (Easily tested by hand.)

For extensive discussion on this see

viewtopic.php?f=5&t=4559&start=150

I wrote an essay on the whole topic that I see has been downloaded a full 13 times!!! My basic point is the impossibility of an exact 17.75 if it's both the minimum and maximum. It's a crazy goal of impossible accuracy and the error must be downwards not an equal error each way.

download/file.php?id=14356

It explains all that. But I didn't know then about the full variation in width of the prototype flange so the references to the prototype need rethinking as well as rewriting. None of the experts has said any of it is bunkum. But as I am regarded here as a lunatic probably none of them have bothered to read it!

To prove my lunacy I postulate that if Roger Sanders is right, S4 would work better AND could be a lot more practical than people suppose given the full variation possible of BB and an appropriate length trangular gauge widening tool!!! (QV...)

[Julian Roberts]

Noel

The prototype flange variation seems to me to be something quite simple: it gives us an excuse for a pragmatically realistic inaccuracy of BB setting. In just the same way that 3 inches wear was allowed on driving wheel diameter, and thus we can pragmatically realistically use a 5ft 6in wheel where a 5ft 9in one is unobtainable? In complete antithesis of Roger's drift I would say the interesting discussion could be "what is the full margin of error of BB setting in S4 that could nevertheless actually work?"

I'm sure you're right about the scaling business. Discussions about those issues can put one off the idea of eternal life...

[Martin Wynne]

Anyway, a 50 ton wagon on 4 wheels...as against a road vehicle that weight with...12 wheels, some of them double wheels?...

Surely it's this weight that keeps the wheel on the rail and thus necessitates just an approx 1 inch flange in combo with its conicity? If it was as light as a road vehicle on each wheel surely a fundamental rethink would be needed?

Hi Julian,

You might be interested in this RAIB report published this week:

https://assets.publishing.service.gov.u ... nction.pdf

It's interesting to speculate how heavy a P4 wagon would need to be in order to push the outer rail over on a curve?

Martin.

[Martin Wynne]

the interesting discussion could be "what is the full margin of error of BB setting in S4 that could nevertheless actually work?"

Hi Julian,

That depends on the flange thickness and rail profile.

I don't know the figures for S4, but in P4 the range of BB values is indicated by the slot on the right in my previous diagram:



That slot is 0.6mm wide, and P4 flanges are typically 0.4mm effective width, so the range of movement in the slot is 0.2mm. i.e. BB 17.55mm to 17.75mm for such wheels.

regards,

Martin.

[grovenor-2685]

The S4 figures are given in the Standards Digest.
Regards

[Julian Roberts]

The S4 figures are given in the Standards Digest.
Regards

Sure Keith but going back to the prototype how are the S4 figures worked out? There's no mention of the flange width variation I quoted above and the BB variations are dubious aren't they? - showing an EF plus BB greater than the Check Gauge at BB max. The translation into 4mm decimal equivalent shows BB max plus EF 0.02 greater than the Check Gauge. Unless it's been altered since I last looked.

We went round all that in the P4S4 thread.

[Julian Roberts]

Thanks for that link Martin. I'll look at it tomorrow ( I. E. Later today) with interest

[Julian Roberts]

Some pictures of worn wheels and reprofiling one of them, at the narrow gauge railway where I volunteer. The close ups of the worn wheels are just crops of the original single photo - a shame I didn't take more, while the reprofiling pictures are all separate ones

2017-07-14 10.42.32.jpg

2017-07-14 10.42.32-5.jpg

2017-07-14 10.42.32-4.jpg

2017-07-14 10.41.39.jpg

2017-07-14 10.41.54.jpg

2017-07-14 10.42.10.jpg

It's apparent to me from this that with use the tread wears down and into the flange which therefore becomes thinner and deeper; meanwhile a double flange is being created...

[Le Corbusier]

Tim

First please rest assured I don't disagree with any of your BB conclusions. If it works better hallelujah.

I like you have been looking for the ways to get utter reliability of running.

However I start from the point that one of the things I like about trains is that they are big. Big boys toys. Really big! And very very heavy. Very very very very heavy. And that's why they behave as they do! A huge amount of power is required to break the inertia of all that weight. And it's the power kick that thrills...isn't it!? So trains start and stop with great difficulty. But roll along effortlessly. The magic of steel wheel on steel rail. That's the big thrill about trains for me. And the fact that this effortless movement is why they are so vital in saving transportation energy where big traffic flows are concerned (though disappointingly the energy required increases with very high speed.)

Anyway, a 50 ton wagon on 4 wheels...as against a road vehicle that weight with...12 wheels, some of them double wheels?...

Surely it's this weight that keeps the wheel on the rail and thus necessitates just an approx 1 inch flange in combo with its conicity? If it was as light as a road vehicle on each wheel surely a fundamental rethink would be needed?

So I can't see the contemporary attraction of making models light. Certainly brass is a much better material for lovely detail modelling than white metal but the loss of the latter's weight seems to me a downside and I try to mitigate the lack of it. The diminutive High Level Barclay Tank (my last creation) I stuffed with lead to weigh as much as I possibly could; around 250g I think.

The limit on wagon weight is what lead you can attach without it being visible in the case of open wagons. A flat wagon is the most difficult as lead can only be put underneath to the loss of some detail but hopefully not obvious except to the most prying eyes. So a maximum attainable is about 50g. An empty mineral wagon can have the floor covered in a layer of lead flashing without anyone noticing (except P4 sleuths! ) so that's much easier.

So I can't really see any reason to try to get good running without 50g minimum weight for each wagon and the fact it will immediately hold the rails much better seems to me to make it a no brainer. Propelling vehicles is an essential requirement for shunting at Monsaldale surely? - much more hazardous without good weight.

The upper weight limit is that a train must have fairly equal weight or lighter vehicles could fall over on curves.

Then with locos it's obvious that the more they weigh the more they can pull AND the more they will stick down on the rails. Again a win win no brainer but some odd delicacy seems to have taken hold of the fraternity rather like "nouveau cuisine" where you get delicious food but are left desperate in an Oliver situation 'can I have more'! - an exquisite model as light as a feather or piece of jewellery. That's not like the real thing. The real thing is hard brutish dirty dangerous unforgiving and utterly lethal in the wrong hands!

So that's my reaction to your suggestion the model should behave well without added weight. Please don't be offended! I just got a bit carried away that's all (its been a long day and not over yet...Glasgow to Eastbourne and back! - with a catering crew strike on Virgin trains!!). Your thread is great (not keeping up with it all) and your learning process interesting to all; responding helps me define my own dormant attitudes. Most of us are just amateurs tho the pros keep us on the straight and narrow. Best of all when they disagree with each other!!

As for the track issues the critical thing about the check gauge is when a vehicle goes through a diverging route, IF the flange is hard up against the outer rail OF THE CURVE (I. E. the closure rail and crossing V, not the stock rail) because of its tangential or centrifugal force, the check rail prevents the guiding flange from hitting the crossing V. (Easily tested by hand.)

For extensive discussion on this see

viewtopic.php?f=5&t=4559&start=150

I wrote an essay on the whole topic that I see has been downloaded a full 13 times!!! My basic point is the impossibility of an exact 17.75 if it's both the minimum and maximum. It's a crazy goal of impossible accuracy and the error must be downwards not an equal error each way.

download/file.php?id=14356

It explains all that. But I didn't know then about the full variation in width of the prototype flange so the references to the prototype need rethinking as well as rewriting. None of the experts has said any of it is bunkum. But as I am regarded here as a lunatic probably none of them have bothered to read it!

To prove my lunacy I postulate that if Roger Sanders is right, S4 would work better AND could be a lot more practical than people suppose given the full variation possible of BB and an appropriate length trangular gauge widening tool!!! (QV...)

Julian ... What a great pep talk ..... almost poetic in places. Nobody has ever summed up for me the essence of railways so succinctly and yet with such tangible excitement before Inspirational

I find it very interesting what you say about weight (in the same way as I have found the notes you sent on track building extremely helpful). From my position I see very little to disagree with and much which I have been intending to move on to.

I suppose if I were to define my approach it might be called incremental .... That is to say although I understand that everything is dynamic and inter-related, I like where ever possible to break things down into (perhaps artificial) separate elements , and then define, check and reassemble back into the whole in the hope that piece by piece preventable errors can be removed systematically.

Firstly I have been trying to iron out as many imperfections in the track as possible. I have at the same time been trying to iron out as far as possible all the inaccuracies I can measure and test within the wheel set up (this is where I am up to now). My test for this has been that the vehicle as built should run through the track on its own at a slow and medium pace smoothly and without derailment. Once I am happy with this, I then intend to add weight to hopefully improve track holding and take out eccentricity caused by speed, braking, acceleration, and the pull & loadings of other attached vehicles etc. I also want to add weight because I think that heavier stock looks better than lighter stock - more real and less toy like when moving (I wonder why this is).

Being an architect a metaphor which helps my grasp of this is that of the flying buttress in gothic cathedrals. The master masons (in principle) used the flying buttress to trace the line of thrust of the roof vault, following it outside of the building envelope and thus bringing it down to the ground (in this way the apparently weightless expression of the heavy stone vault internally, floating above the delicate tracery of the stained glass windows was made possible). However, other forces also came into play on the structure and these were dynamic and not easily predictable ... forces such as wind loadings and snow loadings (both of which can be significant). The Masons answer was (through a process of trial and error - not calculation) to load up the buttresses with weight, thus creating a downward force which made such eccentric loadings incidental ... and this is what underpins the fantastical decorative pinnacles which so enhance and define the outside of the cathedrals. I like this analogy because there is a basic understanding of the engineering principles involved and yet the solution was a pragmatic, trial and error, rule of thumb one. Interestingly, although modern structural engineering can now calculate such matters extremely accurately, factors of safety are then re-introduced into the equations, such that in many ways, we are still dealing with pragmatic rules of thumb even today.

I am at the beginning with all of this at the moment and all is trial and error - trying to develop a pragmatic approach which will work for me. Little gems of input by more experienced modellers are absolutely invaluable. Interestingly my current trial loco is white metal and so comes with considerable weight built in - I will be really interested to see how I get on with the 0-6-0T I am currently underway with, which is etched brass (though the wagon and coach I am also using are both etched kits and both have yet to have any weight added). I will also be fascinated to compare the CSB springing I intend to use on the tank engine, with the very simple 'Perseverance' designed compensation fitted to the white metal loco. To date the white metal loco has just the weight as it came with no refinement of distribution ... yet it seems to hold the track well.

.... so much to experiment with. I will try and load a bit of video of things running through my point work on the Monsal Dale thread ... to see what people think.

[Noel]

Then with locos it's obvious that the more they weigh the more they can pull AND the more they will stick down on the rails. Again a win win no brainer ...

The power output curves of motors vary, and similar sized motors may have quite different outputs, but the heavier the loco and the train it is pulling, the more power is required to move it, and, generally, the larger the motor that is needed plus, possibly, a more robust gearbox. Fitting both weight and a larger motor in a 4mm model of a British loco can be difficult, if not impossible in some cases, and if you use DCC that takes up room as well. Some compromise may be necessary to get to whatever you feel is the optimum for your situation. There may also be issues with what happens to the motor if the loco stalls unexpectedly and there is a delay in the operator responding.

[Paul Townsend]

A few posts back Julian wrote, inter alia:
"Then with locos it's obvious that the more they weigh the more they can pull AND the more they will stick down on the rails."

I disagree with the first clause but am slightly agreeing to the second.

I find that both tractive effort and road holding are far more affected by good suspension than brute weight. One of my lightest locos (CSB) has better behaviour in both respects than similar heavy ones with simple beam compensation.

[Enigma]

Regarding weight = pull, didn't a Class 37 diesel win the Deputy Chairman's Cup once (including the 'pull test') and weighed practically nothing? It was quite a few years ago so can't remember all the details. Owned by Robin (?! - High Peak layout?).

As for b-2-b's, I'm using my trusty original L-shape which I've had for MANY years and which I have no intention of changing. Plenty of my wheels (especially some drivers) have wobbles but with well over 20 P4 locos and a fair few wagons and coaches that all seem to work well and stay on the track, I don't see that opening out my b-2-b dimensions will make any appreciable difference.

However, as some of you know, my current P4 layout doesn't exactly have long and/or fast trains so perhaps my experiences differ from a lot of peoples'. Saying that, the same stock ran well on my one-time 12' x 10' continuous run layout with 3' radius curves.

[Le Corbusier]

Regarding weight = pull, didn't a Class 37 diesel win the Deputy Chairman's Cup once (including the 'pull test') and weighed practically nothing? It was quite a few years ago so can't remember all the details. Owned by Robin (?! - High Peak layout?).

As for b-2-b's, I'm using my trusty original L-shape which I've had for MANY years and which I have no intention of changing. Plenty of my wheels (especially some drivers) have wobbles but with well over 20 P4 locos and a fair few wagons and coaches that all seem to work well and stay on the track, I don't see that opening out my b-2-b dimensions will make any appreciable difference.

However, as some of you know, my current P4 layout doesn't exactly have long and/or fast trains so perhaps my experiences differ from a lot of peoples'. Saying that, the same stock ran well on my one-time 12' x 10' continuous run layout with 3' radius curves.

Out of interest Paul ... what does your L-shape gauge measure?

[Julian Roberts]

the interesting discussion could be "what is the full margin of error of BB setting in S4 that could nevertheless actually work?"

Hi Julian,

That depends on the flange thickness and rail profile.

I don't know the figures for S4, but in P4 the range of BB values is indicated by the slot on the right in my previous diagram:



That slot is 0.6mm wide, and P4 flanges are typically 0.4mm effective width, so the range of movement in the slot is 0.2mm. i.e. BB 17.55mm to 17.75mm for such wheels.

regards,

Martin.

Exactly Martin. And looking at my question this way it's obvious the maximum in S4 will be 18.25 (the prototype CG in 4mm scale) and minimum will be the Check Span 17.67 plus similar clearance, so 17.75. So the slot is 0.5. So in S4 there should be 0.1 margin of error as against 0.2 in P4.

Of course this is all making it seem so easy. But everyone loves the idea it should be very difficult.

[Le Corbusier]

Regarding weight = pull, didn't a Class 37 diesel win the Deputy Chairman's Cup once (including the 'pull test') and weighed practically nothing? It was quite a few years ago so can't remember all the details. Owned by Robin (?! - High Peak layout?).

Thinking about this might this not be (like I think on the prototype) something to do with wheel size and number. I always understood that the more wheels and the smaller these wheels were the greater the traction? Hence the 9fs. I always understood that the greater performance of diesel and electric had as much to do with the gearing allowing much smaller wheels to be used and the drive allowing more of them to be powered than on a steam engine? If so, the class 37 should have more pulling power without the need for excessive weight? Could be wrong of course both in my understanding and because such things don't scale down.