EM wheels on P4 track

[Martin Wynne]

Martin Goodall has written about using EM wheels on P4 track.

If you do that it is important to maintain the checking function by reducing the back-to-back and NOT using the normal P4 back-to-back dimension. Indeed, the B-B with EM wheels needs to be very tightly controlled.

The essential requirement is that BEF should not exceed CG, otherwise there is a risk of wheel flanges hitting the nose of crossing vees. This is especially likely on curved turnouts.

The standard P4 min CG dimension is 18.15mm. BEF MUST NOT exceed this, so with EM flanges (0.5mm thick) the MAXIMUM B-B is 17.65mm. This is LESS than the standard P4 MINIMUM B-B of 17.67mm.

Furthermore, the maximum P4 check span can be 17.55mm (18.20 CG max - 0.65 CF min). The B-B MUST clear this.

So using EM wheels on fully compliant P4 track, the Back-to-Back must be MORE than 17.55mm and LESS than 17.65mm. That means say 17.60mm nominal with an absolute maximum tolerance of +/- 0.05mm (2 thou).

Allow a normal running clearance and you have no tolerance at all! To use EM wheels on P4 track reliably, the B-B must be EXACTLY 17.60mm. It's asking a bit much.

regards,

Martin.

[David Thorpe]

That's all very well, but Martin Goodall assures us that his track is built to P4 standards: "First, my track is built to P4 standards. Flangeway and check rail clearances are all within P4 tolerances; they have not been adjusted in any way to accommodate the EM-profile wheels". As far as I'm concerned, put practice up against theory and practice wins every time.

DT

[rjh]

Dt,

It's not theory, it's the simple fundemental arithmetic of how wheelsets interact with pointwork, just read: http://www.clag.org.uk/p4standards.html
You'll note that the Condition 2 text further states:
" (In practice, because of the shape of the root of the flange, the likelihood of wheel A taking the wrong route increases only as BBmax approaches the value of CGmin .) "

In the hybrid P4/EM case, there is a possibility of the flange striking the nose of the crossing, but that doesn't necessarily mean a derailment. It may mean a enforced sudden lateral displacement.
But the gains from using a deeper flange may outweigh, to Martin Goodall, the drawbacks of using a thicker flange.
Obviously a deeper flange could be combined with a 0.4mm wide wheel but that would not be available off-the-shelf.

Regards, Rodney Hills

[David Thorpe]

The difficulty with your case, Rodney, is that whatever the arithmetic calculations may point to, actual practice seems to produce a different result. You suggest that the use of EM wheels will cause problems. But Martin (Goodall) was specifically asked at one point: "Are you claiming that by using EM wheels you get 100% faultless running?” to which he replied :"Yup; that’s what I’m saying. I reckon you can get 95% reliability with P4 wheels (maybe a little more), but 100% with EM-profile wheels, always provided you have set the back-to-back correctly, and your track does conform exactly to P4 standards." The fact that EM profile rolling stock wheels work well on track laid to P4 standards has been confirmed by two other posters, while none of the doubters appear as yet to have taken up Martin's challenge to try it for themselves.

Heresy is never easy to accept, mind you!

David.

[rjh]

David,

One dictionary defines heresy as:
1.
a. An opinion or a doctrine at variance with established religious beliefs, ..
b. Adherence to such dissenting opinion or doctrine.
2.
a. A controversial or unorthodox opinion or doctrine, as in politics, philosophy, or science.
b. Adherence to such controversial or unorthodox opinion.

I guess you mean 2(category:science)? ;-)

Meantime, I as a simple engineer, am more interested in studying the geometry of the components that are interacting in Mr Goodall's "heretical" cocktail.

I think I'm right to deduce that Mr Goodall ascribes the "sure-footedness" of his stock to the use of deeper flanges - ["Flange depth (0.25mm deeper)"] although he doesn't directly say so.

Assuming EMGS EM wheel standards (see: http://www.emgs.org/ "What is EM?", scroll down to "data sheet 3")
Flange depth = 0.027" (0.021" + 0.006") = approx 0.686mm
Alongside (data sheet 4) are their wheel standards for "18.83 gauge"
Flange depth = 0.0144" = approx 0.366mm

http://www.clag.org.uk/p4standards.html give:
flange depth = 0.38mm (" based on BS 276 contour A.")

The P4 flange is approx 55% of the depth of the EM flange. [edited]
,
Looking at it another way,:
Consider two parallel axles on a four-wheel wagon, P4 flanges, on dead level track.
Nw incline one axle to the other at a gradient of 1 in 47.
(47 = 18mm / 0.38mm).
The high wheel is now unconstrained by the rail head and can readily derail.

Now set the axles parallel again, but make the track twisted over the distance
of the wagon wheelbase to again create a 1 in 47 lateral slope.
Ergo, wheel flange is unconstrained by low rail.

using the EM flanges, the lateral gradient would need to be 1 in 26 to achieve the
same risk effect.

Some folks have been here before, eg Mr. Sid Stubbs of Manchester Model Railway Society,
in the late-1940s and 1950s, see: http://www.mmrs.org.uk/technical/wheels.htm
"
Sid consulted the relevant British Standards Institution’s specification that related to full size railway wheels of the day. He turned tyre profiles of exactly 1:76.2 of the full size dimensions in that specification, and wheels with such tyre profile were tested on the 18mm gauge track on which this group had standardised. They ran well but not as well as hoped, so Sid tried again but this time he used those dimension in the BSS which were listed for wheels that had reached maximum allowable wear and were due to be re-profiled. This wear does not occur on the toe of the flange, only on the coning, and it has the effect of making the flange minutely deeper.

This new form gave running which was very acceptable to the group and became the standard flange form for their wheels. Someone christened it “The Manchester Profile” and that is how it is known to this day.
"

Further down the same page is a diagram of the 'Manchester' wheel profile.
It has flange depth = 0.022" = approx 0.559mm
This would have a lateral gradient value of 1 in 32.
Not that different from the EMGS value.
Manchester wheel has flange thickness = 0.018" = approx 0.457mm

A comparative overlaid diagram including Manchester and Prototype wheel profiles is given in
an early MRSG Protofour article: http://www.scalefour.org/history/Sep66/MRN9-66.htm
Here they look to be very similar in thickness.

How untwisted is your track?
How parallel are your rigid axles?
How worn do you model your wheels?

Thinks - P4 wheelsets worn down to scale protoypical wear limit -
0.56mm worn flange is 47% deeper that 0.38mm unworn flange, as per Sid.
Martin G's EM ones are 80% deeper than 0.38mm unworn.

EM depth flanges are "only" 22% overscale models of fully worn wheels.
P4 crossing flangeway (0.68mm) is "only" 17% overscale ;-O

Hmm.

Regards, Rodney

[Russ Elliott]

Martin Goodall has written about using EM wheels on P4 track.

To be fair to Martin Goodall, he is using certain types of EM tyre cuts, set at a conformant but otherwise unspecified back-to-back, on certain types of wheelbase, and running on track configurations and radii not known to us. (I haven't seen MRJ 196 yet.)

[martin goodall]

According to my vernier gauge, my P4 back-to-back gauge measures 17.7mm. I confirm that I have set all my track clearances using P4 gauges throughout. Although I recall that I did set the checkrails and crossing flangeways on some turnouts 'inside out' (i.e. check rails to the crossing flangeway gauge, and crossing flangeways to the checkrail gauge) with the specific object of keeping wheels flanges [all P4 at that time] well away from the noses of the crossing vees.

I have two turnouts on my layout forming a crossover on a fairly sharp curve. They are both C10s, so if any crossings were going to give trouble, these would be the ones to do it; yet I have had no problem with EM-profile wheels on entirely uncompensated RTR rolling stock safely and smoothy negotiating this cross-over in every direction.

Smokey Bourne was once quoted by Cyril Freezer as saying that "An ounce of practice is worth a ton of theory" and I have always followed that guiding principle. I am not afraid to experiment, and to see how things work.

You can produce as many calculations as you like to prove that EM wheels won't run on P4 track, but my practical exerpimental experience proves that they will (at least those with modern 'fine-scale' flanges, which incidentally are not as deep as the figures quoted above).

Finally (for the moment), I am reminded of the well-known scientific fact that a bumble bee can't fly - the power/weight ratio is all wrong, it's the wrong shape, the wings are too small, etc. etc. Unfortunately, no-one told the bumble bee, which just goes on merrily buzzing about completely unaware of this scientific impossibility.

[Brinkly]

I'm not totally sure of this, but in all fairness to EM wheels on P4 track Rich Pedder (Fatadder) was sent EM wheels which he fitted to a new Hornby HST dummy car, without knowing it. And it ran quite smoothly round TT1 for several runs then after about 10 minutes of running Rich took it off and then realised that the wheels where wrong, so putting this theory into practice it does work, and the track on TT1 was rubbish, so there is an element of truth in what is being said as I and others at DRAG did witness the unit running on EM wheels.
Rich will need to clarify it, but I am about 99% sure that this was the case.
Kind regards,

Nick

[craigwelsh]

Following the main discussion thread there was mention of Exactoscale wheels being "too narrow".

I've put some in my calipers and they show 1.66mm with Kean Maygib at about 2mm there abouts.

Now from what I understand the crossing nose is the main bit to be wary about and you have to make sure the wheel width is greater than twice the flangeway - 2 x 0.68mm = 1.36mm so the Exactoscale wheels should still give you a decent margin. I've certainly not had issues with them in this capacity although early 3-hole were a bit too fine to avoid a bit of wobbliness, some of mine appeared translucent! Now fixed with thicker plastic on later batches and i've used a bit of epoxy to beef up early ones.

Incidentally i'd recommend a B2B in the middle of the range for P4 rather than the minimum and Exactoscale do a 17.75mm B2B gauge for this. You could even go up to the S4 or maximum B2B if you wanted.

I can understand that if the specific EM wheels have the small enough flange this will work fine, even if they are tight in the check areas they can probably ride up it a bit without issues as you would expect from putting a coarser standard in.

Personally its only cleaning the P4 wheels that I find a chore, the running is fine when the flange isn't obscured with crud. I do subscribe to 'getting it all right' so i'll stick to springing things and keep the finer profile wheels but that's personal preference.

[Martin Wynne]

You can produce as many calculations as you like to prove that EM wheels won't run on P4 track, but my practical experimental experience proves that they will

Hi Martin,

No it doesn't. What you have proved is that "these particular EM wheels" will run on "this particular P4 track" and no-one is doubting that.

What you haven't proved is that ALL EM wheels will run reliably on ALL P4 track. It's quite possible to have wheels which conform to the EMGS profile and track which conforms to the P4 standards limits, and find that they bump the crossings -- not necessarily enough to derail, but enough to say that the running is not smooth and reliable.

If the BEF figure for your wheels is no greater than the CG figure for your track, then your wheels will run fine. If it isn't, they won't. But you haven't published these actual measurements for your own wheels and track.

Also, since these figures are likely to be near to or only just over the limit, a great deal will depend on the actual profile of your crossing noses. If you have reduced the top height and rounded the running edges in the prototype fashion, a slight interference with the flange root radius may go unnoticed. If you have simply filed rail to an angle at the nose, it won't.

regards,

Martin Wynne.

[Martin Wynne]

Now from what I understand the crossing nose is the main bit to be wary about and you have to make sure the wheel width is greater than twice the flangeway - 2 x 0.68mm = 1.36mm so the Exactoscale wheels should still give you a decent margin.

Hi Craig,

If you are "getting it all right" the crossing noses should be blunted back in the prototype fashion (to 3/4" nose width for most bullhead), and this certainly makes a vast improvement in the look of the thing over razor-sharp vees. This is also necessary to match the rails to the templates and have the vee nose supported on the "A" timber. A razor-sharp vee nose, if properly aligned to the template, will be hanging in fresh air between the timbers.

So the minimum wheel width for full support is actually twice the flangeway PLUS the blunt nose width. You also have to allow for any small chamfer between the wheel face and tread, and for the top corner radius on the rail, in order to be sure that the wheel tread is firmly supported on the wing rail top.

So the minimum wheel width then becomes 0.68mm (P4 max flangeway) + 0.68mm (P4 max flangeway) + 0.25mm (blunt nose) + 0.05mm (wheel chamfer) + 0.04mm (rail corner*) = 1.70mm.

The 1.67mm dead-scale 5" Exactoscale wheels don't quite make it for P4 but are fine for S4 with prototypical 0.58mm flangeways, for which minimum wheel width is then 1.50mm.

*The BS-95R top corner radius is 1/2", scaling to 0.16mm, but because it is a radius and not a sharp chamfer, it is not necessary to make a full allowance.

regards,

Martin Wynne.

[Paul Willis]

If you are "getting it all right" the crossing noses should be blunted back in the prototype fashion (to 3/4" nose width for most bullhead), and this certainly makes a vast improvement in the look of the thing over razor-sharp vees. This is also necessary to match the rails to the templates and have the vee nose supported on the "A" timber. A razor-sharp vee nose, if properly aligned to the template, will be hanging in fresh air between the timbers.

Hi Martin,

When you say "blunted" I presume that you mean "rounded off" rather than squared-off or chamfered?

I've looked closely at all of the trackwork pictures that I have on this laptop (my railway library is back at home) and I can't see enough detail in close-up to determine exactly how it is shaped.

Cheers
Flymo

[Martin Wynne]

When you say "blunted" I presume that you mean "rounded off" rather than squared-off or chamfered?

Hi Flymo,

I mean the vee nose is squared off to the specified width before the other rounding and profiling takes place. Here's a close-up from a Templot template:


Blunt nose of V-crossing. Diagram showing that the FP (gauge-face intersection) is normally in fresh air between the timbers, but the actual blunt nose of the vee is always supported on a timber.


Here are a couple of pics showing that for an almost new bullhead crossing. I have added gauge lines in yellow and you can see that the vee is blunted back from the intersection point, and the top of the nose is profiled to be lower than the wing rails.




© Mick Nicholson
Gauge lines showing blunt nose and reduced height of crossing vee. Thanks to Mick Nicholson for the pic.

For some more discussion of this particular photo, see also: http://scalerail.phpbbhosts.co.uk/viewt ... 4107#p4107

regards,

Martin.

[craigwelsh]

If you are "getting it all right" the crossing noses should be blunted back in the prototype fashion (to 3/4" nose width for most bullhead), and this certainly makes a vast improvement in the look of the thing over razor-sharp vees. This is also necessary to match the rails to the templates and have the vee nose supported on the "A" timber. A razor-sharp vee nose, if properly aligned to the template, will be hanging in fresh air between the timbers.

So the minimum wheel width for full support is actually twice the flangeway PLUS the blunt nose width. You also have to allow for any small chamfer between the wheel face and tread, and for the top corner radius on the rail, in order to be sure that the wheel tread is firmly supported on the wing rail top.

Well I certainly do fit the correct blunt nose on my REA points and the GWR ones i'm trying at the moment but didn't realise the significance of this to that sum so thanks for putting up the full equation. My apologies to Martin Goodall, it appears you were dead on about those wheels then though they do seem fine for me. Mind you Scalefour Stores do supply an S4 check gauge if you ask for a P4 one as the material is 0.58mm wide. I've been using a Brooke Smith one now that is correctly wider.

So apart from having the sleepering wrong with fishplates in the wrong place and the wheels technically too narrow for P4 is there anything else I should be worried about with Exactoscale?!

The debate has spurred good debate and info in any case.

[LesGros]

Martin,
What an excellent picture to bear witness on how a wheel passes through the prototype crossing.

My, previously dented by Martin G, confidence in P4 standards is now restored by this picture and your posts on the EM/P4 saga. Thankyou.

regards

[Paul Willis]

When you say "blunted" I presume that you mean "rounded off" rather than squared-off or chamfered?

Hi Flymo,

I mean the vee nose is squared off to the specified width before the other rounding and profiling takes place. ...

Here are a couple of pics showing that for an almost new bullhead crossing. I have added gauge lines in yellow and you can see that the vee is blunted back from the intersection point, and the top of the nose is profiled to be lower than the wing rails.

© Mick Nicholson
Gauge lines showing blunt nose and reduced height of crossing vee. Thanks to Mick Nicholson for the pic.

Martin,

Thanks very much - that was exactly what I was thinking, but I wanted to confirm with someone as knowledgable on trackwork as yourself. The used of the yellow lines certainly does illustrate the difference between "knife""and "rounded" ends.

I've always tried to build turnouts running back from the vee tip positioned over the timber, as it is obvious that it should not be unsupported, but the extra clarification of the "look" that I should be aiming for is very helpful.

Cheers
Flymo

[martin goodall]

[quote="Martin Wynne"] "What you have proved is that "these particular EM wheels" will run on "this particular P4 track" and no-one is doubting that. What you haven't proved is that ALL EM wheels will run reliably on ALL P4 track."

I would never claim that all EM wheels will run on P4 track, only 'fine-scale' EM wheels made to modern standards, not RP25 profile, not over-wide tyres (Markits), not over-deep and over-wide flanges (various older EM wheels). Wheels which fill the bill include Ultrascale (when available), Kean-Maygib and Alan Gibson (although the last need checking for manufacturing quality, concentricity, etc.)

There's a very easy way of finding out whether my idea really works. Do what I did originally - Get hold of a handful of EM wheels from a friend, re-gauge them to P4 back-to-back, fit them in a wagon or coach and see what happens. It's much quicker than poring over measurements and calculations.

I got the odd bump or jump at first on plain track due to the rails being slightly narrow to gauge (easily corrected - and it should have been at least 18.83mm in the first place), but never any trouble at crossing noses.

We can all go on theorising till the cows come home - the only way of proving if something actually works, or disproving it, is by practical experiment. That's what I did.

[Martin Wynne]

There's a very easy way of finding out whether my idea really works. Do what I did originally - Get hold of a handful of EM wheels from a friend, re-gauge them to P4 back-to-back, fit them in a wagon or coach and see what happens. It's much quicker than poring over measurements and calculations.

Hi Martin,

But you have still only proved that it works on your actual P4 track, which may have been made to one end of the P4 limits. You may take your EM-wheeled stock to a friend's P4 layout, which has been built to the other end of the limits, and find it no longer runs so well. Whereas the P4 standards are designed to ensure that any P4 stock will run on any P4 track, anywhere.

To get the best results on most P4 layouts, I suggest setting the EM wheels closer than the P4 back-to-back, say 17.60mm/17.65mm (see my original post in this topic). This will also help a bit with clearance inside bogie sideframes, etc.

regards,

Martin.

[martin goodall]

I have never understood this point about being able to run your stock on other people's layouts (and vice versa). I have always believed in 'horses for courses'; i.e. stock should be built for the layout on which it is intended to run. I am willing to bet that some P4 rolling stock which runs perfectly on its builder's own P4 layout will prove to be less well behaved on a different P4 layout, whether because of slight discrepancies in the set-up of the wheels or in the way the track is laid.

I suspect this may well be the reason for less than perfect running on some exhibiiton layouts, because different members' stock is run on the layout without adequate testing and adjustment to ensure complete compatibility of the stock with the track on that particualr layout. It is not just a question of checking with gauges, but actually running the stock on the layout before the exhibiton and ironing out the faults. Nobody should be under any illusion that just because everything is built to P4 standards it will all work perfectly without further ado.

Most of us just run our own stock on our own layout, and so we don't have to prove that the particular combination of track and wheels we have developed will work with different rolling stock on a different layout.

As I have said before, I have set my EM 'finescale' wheels to the P4 back-to-back (17.7mm on my BB gauge) and have had no problems. I see no need to mess about with the back-to-back or with check rail and flangeway clearances. So far as I am concerned (based purely on practical experience of running a variety of EM-wheeled stock on my own layout), EM fine-scale wheels will run perfectly happily on unmodified P4 track when set to the P4 back-to-back.

There is really no point in debating this. You can only prove it or disprove it by trying it out for yourself.

[jim s-w]

The difficulty with your case, Rodney, is that whatever the arithmetic calculations may point to, actual practice seems to produce a different result. You suggest that the use of EM wheels will cause problems. But Martin (Goodall) was specifically asked at one point: "Are you claiming that by using EM wheels you get 100% faultless running?” to which he replied :"Yup; that’s what I’m saying. I reckon you can get 95% reliability with P4 wheels (maybe a little more), but 100% with EM-profile wheels, always provided you have set the back-to-back correctly, and your track does conform exactly to P4 standards." The fact that EM profile rolling stock wheels work well on track laid to P4 standards has been confirmed by two other posters, while none of the doubters appear as yet to have taken up Martin's challenge to try it for themselves.

Heresy is never easy to accept, mind you!

David.

Since it was I who asked the question I cant believe Martin has NEVER had a derailment this way. And as a doubter I tried EM wheels on P4 over a decade ago and found it much more hassle than using P4 wheels. A point I keep making to which Martin keeps ingoring.

Been there - tried that, found it can be made to work but not worth the extra effort IMHO.

Cheers

Jim

[jim s-w]

Finally (for the moment), I am reminded of the well-known scientific fact that a bumble bee can't fly - the power/weight ratio is all wrong, it's the wrong shape, the wings are too small, etc. etc. Unfortunately, no-one told the bumble bee, which just goes on merrily buzzing about completely unaware of this scientific impossibility.

AFAIK it was never a fact and just an urban myth. If it ever was its certainly not upheld now.

Cheers

Jim

[jim s-w]

Hi Martin

I dont know where you are based but we are showing Moor Street at Eastley at the end of Feb. We are also showing Amlwch at Derby, the plank at Scalefour North and New Street (as work in progress) at the Kernow show in September. You are more than welcome to bring your stuff along for a play if you want to. (locos will need to be DCC though)

Cheers

Jim

[Midland]

Finally (for the moment), I am reminded of the well-known scientific fact that a bumble bee can't fly - the power/weight ratio is all wrong, it's the wrong shape, the wings are too small, etc. etc. Unfortunately, no-one told the bumble bee, which just goes on merrily buzzing about completely unaware of this scientific impossibility.

AFAIK it was never a fact and just an urban myth. If it ever was its certainly not upheld now.

Cheers

Jim

No a mis-quote. Bumble bees cannot be shown to be able to glide. That is because they can't glide! They can demonstrably fly but if they stop flapping their wings they fall like a brick. Aeroplanes on the other hand 1) don't flap their wings and 2) don't fall like a brick when the engines stop and birds also don't fall like bricks when they stop flapping their wings!

Alan

[jim s-w]

No a mis-quote. Bumble bees cannot be shown to be able to glide. That is because they can't glide! They can demonstrably fly but if they stop flapping their wings they fall like a brick. Aeroplanes on the other hand 1) don't flap their wings and 2) don't fall like a brick when the engines stop and birds also don't fall like bricks when they stop flapping their wings!

Alan

Hi Alan

Like the way Cinderella's slipper was Fur not Glass? A mis-translation means its glass now. It is also thought that Moses parted the Reed Sea not the Red Sea. People on foot were easily able to pass through the reeds but chariots couldn't follow.

I like these sort of things. (probably because I am hopeless at spelling myself!)

Cheers

Jim

[martin goodall]

The bumble-bee quip was just a joke and, if you think about it, it cannot be "a scientific fact" that a bumble bee can't fly, because it obviously does.

But then, of course, nor is it a scientific fact that there has to be double the flange width to get wheels through crossing flangeways and checkrails. My own experience shows that this is another "scientific fact" which is really just an urban myth.