Wheel profiles

[andrew jukes]

I've been cheating a bit. The train is at should be (four twins + observation car) but I have a Deltic on the front!

When I have Empire of India hauling the train (and someone here with a decent camera) I'll aim to post some pictures.

Regards

Andrew

[Paul Willis]

No mention of the gravity tapered BtoB gauge, is it still available from the stores? An essential piece of kit.

Hi Tim,

Yes it is. Still available, still a good seller, and as you say still an essential bit of kit for checking wheelsets that have already been assembled.

The instructions are here: http://www.scalefour.org/downloads/gravitygauge.pdf if anyone doesn't know what we're talking about.

Cheers
Paul Willis
Deputy Chairman

[Trevor Grout]

Bet that was a sight to behold Andrew, you should video it and setup a youtube channel so we can all enjoy.

regards
trevor

I've been cheating a bit. The train is at should be (four twins + observation car) but I have a Deltic on the front!

When I have Empire of India hauling the train (and someone here with a decent camera) I'll aim to post some pictures.

Regards

Andrew

[allanferguson]

Concerning the physical tool to set back to backs, it is useful to distinguish between a thing used in the construction of a wheelset, which is usually an L-shaped piece (Scalefour Stores) or a parallel-sided block (Exactoscale, although I believe no longer made under the new C&L regime) or a turned item (current C&L), and the thing used for what I would describe a checking an already-assembled wheelset (as one gets for coaches and wagons from AG etc). For this checking BB gauge, I use some bits of turned round brass (0.5" diameter is ideal), twiddling the wheelset between finger and thumb on one hand and assessing it with the gauge twiddled between finger and thumb of the other hand. Rotating the turned gauge throughout the circumference perimeter of the flange rear is a good way of assessing BB conformance and wobble error. The cost of the brass is negligible, so messing a few up (to the wrong dimension!) is not a problem, and one can finesse the turnings as much as one desires into 'go' and 'no-go' items.

Whatever you use, trust nothing and check everything. L-shaped things can be a different dimension at one end to the other. (And most cheapo digital calipers will have a reading tolerance of 0.02mm or 0.03mm, so using a micrometer is usually better when measuring gauges.)

I have for some years used digital calipers to check B to B's. I check the wheels at at least three points, and usually find some wobble. The calipers are easy to get in around brake gear etc. I normally aim for 17.75, but have to average out the wobble. And I have three sets of digital calipers (and one dial caliper), so I can average out the error.
The gravity B to B gauge is an excellent device; I made my own from a tapered piece of 40 thou stuck to another piece of 40 thou, the whole fixed to a piece of wood which is tipped up at a shallow angle. But it's no use for locos or bogie vehicles, and wobbly wheels can give misleading results, so it's back to the calipers.
I find that if the track is correctly laid (not always a given) then 90% of derailments are down to back to back measurements.

Allan F

[Terry Bendall]

The train is at should be (four twins + observation car) but I have a Deltic on the front!

Some people of course would be quite happy to see the train with a Deltic on the front!

Terry Bendall

[martin goodall]

But, Martin, why go to all this trouble? Funnily enough, P4 wheels are designed to work with P4 track and P4 track is designed to work with P4 wheels.

As I said in a previous thread, if you are entirely happy with P4 wheels running on P4 track, then by all means carry on using them.

I was not entirely satisfied, and I wanted to see if I could find a less demanding standard (so far as the wheel flanges are concerned - this was really the only factor I was concerned about) which did not necessarily demand the fitting of compensated suspension, and would be more forgiving of minor (and I do stress minor) track irregularities, or any slight (again slight) irregularity in the set-up of the vehicles themselves.

It seems there are a good many people using P4 standards who are prepared to go to endless time and trouble in an effort to make P4 standards work for them. I wanted a 'quick fix' which eliminated all the fiddling about. And that was why I started experimenting with EM wheels. There was very little trouble involved in carrying out the experiments and in re-gauging EM wheels for use in my rolling stock. I can confirm that it has obviated a huge amount of messing about that I used to find necessary when using exclusively P4 standards, and has made the construction and conversion of rolling stock much simpler and easier than it used to be.

I appreciate that another option, in theory, might have been to adopt a different set of standards altogether (e.g. EM), but I had a completed layout (so far as the track-laying and electrics were concerned) built to P4 standards, and I had no wish to re-lay the track to some other gauge. In any case, I have no issue with P4 standards other than the size of the wheel flanges, plus the somewhat excessive running clearance when these wheels are set at the lower end of the P4 back-to-back tolerances (17.7mm using my Studiolith BB gauge).

Ignore all this if you prefer, but I am very happy with the results I have achieved. My only reason for mentioning them in this forum (once or twice!) is that some remarks from other members that I have picked up on suggest that others might benefit from taking a similar approach.

[Philip Hall]

I must take issue with Martin here in that I really do not think that there are that many people who are 'prepared to go to endless time and trouble in an effort to make P4 standards work for them'. This implies (to me, at any rate, never mind what a raw beginner might think) that the standards do need such trouble to make them work. And that simply is not the case; if it was I wouldn't be doing it and neither would a lot more of us. I have been building in P4 for more years than I care to mention and really have not had any more trouble in making it work than I did in 00. Quite the reverse, because all the standard specifications interlock, as it were. I might also say that having converted more than a few RTR engines to P4 for more than a few people, no one has yet come back to me to say that they have any more propensity to fall off the rails than anything else.

We are doing our best to encourage folk to take up P4 for all the reasons you can think of, not just the running qualities, but I really do feel that putting forward EMF wheels as a usable alternative to P4 wheels is not terribly helpful for the beginner. At worst it is confusing (just look at all the stuff on here for a start). At best it is an alternative, if you wish to try it, but, as with anything else like this, you do need to understand what causes vehicles to come off the track before you can devise methods to stop them doing so. Most folk will not need to worry about this sort of thing because, as it comes (out of the box as it were) it does all work. As Terry has said, sometimes you need to think your way around these things. If it doesn't, sometimes, then it's part of making a model and making it work. Which for me is part of the fun.

Philip

[Terry Bendall]

others might benefit from taking a similar approach.

I would suggest that there is nothing to be gained by anyone adopting the approch that Martin has used and certainly not the newcomer. P4 standards have been shown to work time and time again for more than 40 years on layouts of all sorts of sizes and degrees of complexity. It is far better to use an established and agreed set of standards than a mish mash of things.

Terry Bendall

[andrew jukes]

Just a footnote on the Coronation + Deltic:
Apart from three special 'track circuit detectable' bogies (which are still bare metal - another reason for not providing pictures), the coach and loco bogies are all rigid. The coaches originally had plain bearings (and Golden Age's now very nice P4 wheelsets, the back-to-back of which varied a little, with almost all in the 17.70 - 17.80mm range) and now have pinpoint bearings with Exactoscale wheelsets assembled on a 17.82mm back-to-back gauge. The Golden Age wheelsets in initial test running 'found' an under-gauged check rail on the curved diamond (the only adjustment I have had to make). The Deltic is a fairly coarse representation, being a Lima bodyshell on a very much lengthened Athern Alco PA-1 chassis with Gibson replacement wheels and Hornby Cl 37 sideframes.

Just mention this to emphasise that you can do a lot without getting sophisticated with suspensions - and it does definitely work!

Regards

Andrew

[Ian Everett]

Just mention this to emphasise that you can do a lot without getting sophisticated with suspensions - and it does definitely work!

Anyone who has seen Mike Norris' Preston in action will agree with Andrew - diesels and electric locos and most coaches and wagons with no mods other than standard P4 replacement wheelsets, and absolutely NO derailments, other than those caused by operator error and boy, does he have trackwork - see this:

Preston No 1.jpg

Ian

[dcockling]

and boy, does he have trackwork

Yes he does:

Preston Pictures



Danny

[billbedford]

I was not entirely satisfied, and I wanted to see if I could find a less demanding standard (so far as the wheel flanges are concerned - this was really the only factor I was concerned about) which did not necessarily demand the fitting of compensated suspension, and would be more forgiving of minor (and I do stress minor) track irregularities, or any slight (again slight) irregularity in the set-up of the vehicles themselves.

It seems there are a good many people using P4 standards who are prepared to go to endless time and trouble in an effort to make P4 standards work for them. I wanted a 'quick fix' which eliminated all the fiddling about. And that was why I started experimenting with EM wheels. There was very little trouble involved in carrying out the experiments and in re-gauging EM wheels for use in my rolling stock. I can confirm that it has obviated a huge amount of messing about that I used to find necessary when using exclusively P4 standards, and has made the construction and conversion of rolling stock much simpler and easier than it used to be.

It seems to me this is no more than the "I can't be bothered to learn to solder" argument.

Ha'pennies worth of tar springs to mind.

[jon price]

If the spec is authentic, and this should make things run properly, then there is a question of why we need compensation or springing beyond that which is present on the real thing. The answer would appear to be that track is not as good as the real thing. If we cant make accurate track (I'm not saying we can't) then we cant run accurate vehiocles and all bets are off with regards to the bodges we have to apply to make things run properly. If we make accurate track then as far as I can tell the suspension requirement is infinitessimal (the real thing does not bounce up and down like a kangaroo). So either produce accurate track, or bodge your vehiclkes, and if you have to bodge then any bodge is as "accurate" as any other.

[grovenor-2685]

then there is a question of why we need compensation or springing beyond that which is present on the real thing.

We don't, we just do our best to provide suspension that works at our scale. Beyond the most basic chaldron wagon and similar the real thing has suspension! The bodges are a result of modellers wanting to do without any sprung or equalised suspension.
Keith
PS.

(the real thing does not bounce up and down like a kangaroo)

Neither do our models, but in both real and model the wheels need to remain in contact with the rails, and it needs springs or equalisation to achieve that.

[allanferguson]

and boy, does he have trackwork

Yes he does:

Danny

Mikes trackwork is wonderful (how does he find the time, apart from anything else.
I note that his trackwork is laid directly on the baseboard, with no intervening underlay.
Does this, I wonder, help to ensure the stability of the track?

Allan F

[Terry Bendall]

The answer would appear to be that track is not as good as the real thing.

A look at the full size railway will show that the track is not always as good as it might be, particularly on sidings. There are several people on here who work on the big railway and I am sure that they can confirm that. Just try observing a train passing over the joint between two lengths of rail and watch the rail move for a start.

If we cant make accurate track (I'm not saying we can't)

It is not very difficult to make track that is sufficiently accurate to allow stock that has no compensation or springing to run successfully. A flat baseboard and track that is laid flat is all that is needed. Both need some care in the making but it is not beyond the reach of anyone.

Terry Bendall

[andrew jukes]

Jon Price wrote:

… all bets are off with regards to the bodges we have to apply to make things run properly. If we make accurate track then as far as I can tell the suspension requirement is infinitessimal (the real thing does not bounce up and down like a kangaroo). So either produce accurate track, or bodge your vehiclkes, and if you have to bodge then any bodge is as "accurate" as any other.

Terry's right. If you observe real trans on real track (particularly poorly maintained jointed track) you would see how much track and suspensions move.

But there is a more fundamental point. You can scale the linear dimensions of the real thing (and P4 pretty much does this with track and wheels) but the Laws of Physics prevent the resulting model behaving like the real thing. Your model may be exactly 1/76.2 in every dimension but its mass will be 1/76.2^3 or around 1/442,000 of the real thing. Springs, if made exactly to scale, would be much too stiff (compare what happens when a 60ft length of bullhead rail is picked up by a crane with what happens when you pick up an equivalent length of model rail: one sags dramatically, the other hardly deflects at all).

Most of these 'scale effects' work in our favour. How can we run trains at a scale 100mph on 4ft radius uncanted curves when the full-size railway needs a one mile radius curve with 6 inches of cant?

'Scale effects' have to be dealt with whenever you try to scale the dynamics of the real world - for example using a wind tunnel when designing aircraft or a water tank when modelling a tsunami. Call it bodging if you want to but finding a way to make your model look and behave realistically in spite of these scale effects is one of the interesting challenges we face.

Regards

Andrew

[Will L]

If the spec is authentic, and this should make things run properly, then there is a question of why we need compensation or springing beyond that which is present on the real thing. ..

Not at all sure we do. For instance the typical CSB suspension deflection it .5mm scales or a sacle 1.5 inches which is not untypicality of the real thing.

However strait track holding isn't the only treason for doing it, elctrical pickup on rigid framed loco's leaves much to be desired, and haulage capacity isn't optimum either.

Actuality what is being argued by Martin is that we should run trains on which the flange is used, none prototypically, to compensate for a failure to ensure the wheel tread stays firmly on the track which is what is supposed to happen on a real railway. Those who delight in De-Ja-Vu can looking up a previous thread that argued these points which includes the classic Richard Feynman Youtube clips on what actually keeps trains on the rails. These are well worth a watch if you haven't seen them before.

[Terry Bendall]

But there is a more fundamental point. You can scale the linear dimensions of the real thing (and P4 pretty much does this with track and wheels) but the Laws of Physics prevent the resulting model behaving like the real thing.

Andrew is of course quite correct and this is a factor well know to model engineers who build live steam locos. Scaling down the steam passages for example would make the loco unusable and springing on such models is also not to scale. Just think of the load that even a small 2 1/2 inch or 3 1/2 inch live steam loco will pull, usually two or three adults and totally out of scale to the model.

Terry Bendall

[Alan Turner]

Most of these 'scale effects' work in our favour. How can we run trains at a scale 100mph on 4ft radius uncanted curves when the full-size railway needs a one mile radius curve with 6 inches of cant?

Regards

Andrew

You of course have to define what you mean by a scale 100mph. If you mean the model covers a linear scale 1 mile in 36 seconds then that is not scale speed because you have not scaled time.

Try running the train at 8 times the "scale" 100mph if you want to represent the dynamics of the system. I don't think somehow that your model will still be on your 4ft rad uncanted curve for very long. Just like the real thing.

regards

Alan

[Will L]

You of course have to define what you mean by a scale 100mph. If you mean the model covers a linear scale 1 mile in 36 seconds then that is not scale speed because you have not scaled time.

Are, another of those familiar little chestnuts rolled out for re-examination. There is no such thing as scale time.

[JFS]

You of course have to define what you mean by a scale 100mph. If you mean the model covers a linear scale 1 mile in 36 seconds then that is not scale speed because you have not scaled time.

There is no such thing as scale time.

True, but that does not negate what Alan said which was that in order to represent the dynamics you would have to "scale" time. And what he said does not negate what Andrew said which was that the scale effects work in our favour.

So every one is right! There have been many decent PhDs on this topic - none of them written by me!

Best wishes,

[Julian Roberts]

Thanks Russ for your post of June 15. The envelope idea, of a window between 17.67 and 17.87 being the acceptable range of the b2b, was a revelation. I have struggled with the impossibility of getting an exact gauging, erroneously (I now see) I was trying to get 17.67. Your advice makes the process look far more practical.

[martin goodall]

There's a very interesting article by Jeff George in MRJ 234 - "An heretical compromise" (pages 251 to 252).

His reasons for seeking a more satisfactory wheel profile were remarkably similar to my own.

Unlike Jeff, I didn't find it necessary to modify the EM wheels (by Ultrascale, Kean-Maygib and Alan Gibson in my case), provided the back-to back is set to a value close to the P4 minimum (17.67 mm); (my old Studiolith BB gauges all seem to measure 17.7 mm over their ground faces); and also provided the track gauge is nowhere less than 18.83 mm. Flangeway and check rail settings on my layout are to the published P4 standards, and have not had to be eased or modified in any way.

It will be interesting to see what reaction Jeff's article gets from MRJ readers. See what you think when you read his article yourself.

[Horsetan]

Here we go!