Discussion in 'Steam Traction' started by M Palmer, Nov 22, 2018.
Thank you for finding the exact quote that I had a vague recollection of!
Don’t forget the rail head sits at a 1:20* angle too. If the wheels didn’t match the wheel-rail contact surface would be a pin point and braking would be just about impossible. So it sounds like utter cobblers to me.
(*I believe some railways or maybe tramways may use a different profile.)
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Holcroft, Vol 1 page 133 para. 6, describing SR standardisation of tyre profiles, states that Stroudley locos had a parallel tyre .
Ultimately it is the root radius between the tyre and the flange which centralises the wheelset on the rails, and that radius is blended into the tyre with, in effect, a short taper, so you may not necessarily need a taper right across the tyre. There may be other reasons for having one.
It gets complicated because the wheel and the rail are not rigid at the point of contact - they distort to form a contact "patch" to use a road vehicle term - and this effect is greater in full size than in miniature, as the big locos are heavier and the track is more flexible, though generally smoother.
And that is just on straight track, before you start to think about what happens on curves.
Not, I suspect, for very long! I would have thought that the way tyres wear must be a very big part of the equation, since presumably what is required is the best profile on average between re-turnings, rather than something which is perfect for the first 100 miles and gets worse and worse. And of course rate of wear, on wheel and track.
Most miniature tracks do not have rails the rails inclined. From personal experience parallel treads are perfectly satisfactory for miniature locos.
Not forgetting he amount of mainline track that is Vertical.
Admittedly mainly in S+C.
But that is Off topic.
There's a drawing of the Stroudley profiles in HJ Campbell-Cornwall (page 129). Essentially, on the driving wheel proper (i.e. that with a crank axle), the tread is more or less flat (not coned) and the flange is very thin; all other wheels (including the non-crank axle driving wheels) had conventional profiles.
The rationale given seems to be more in relation to the flange thickness: by being very thin, it was thought to impart less sideways stress back to the crank axle by removing grinding against the inside of the rail or on check rails. The aim was thus to reduce the incidence of broken crank axles, something Stroudley believed was achieved. In essence, it behaved like a flangeless driver, but with a residual thin flange such that if the crank axle did break, directional stability would be retained until such time as the loco stopped.
As an aside, and going further OT - when did the 1 in 20 incline of rails become standard? In the rail-wheel interface, surely both are important and have to be seen as a combined system in design terms? Stroudley's design ideas were forming in the 1860s and 1870s, which is still quite early in railway terms.
I think the 1 in 20 inclination of the rail is more to do with resisting the asymmetric loads applied by the vehicle, rather than matching the wheel profile - in any case the railhead has a convex profile, so there is still nominally a "point contact" with the tread.
I have always made miniature loco wheels up to 5 inch gauge with parallel treads and a generous root radius and they work fine. On miniature rails made from bar section with a flat top they may give better adhesion. Note that LBSC was writing mainly for beginners, and a coned tread is an extra complication for a novice with maybe a very basic lathe.
If you think carefully about what is happening to a conventional wheelset on a curve, coned treads or not, you soon see the reasoning for transition curves, superelevation, and self-steering wheelsets. It really shouldn't work as well as it does, in its simple form.
I wonder if Stanier published anything on his experiments with parallel treads?
As someone who firmly understands the principle behind rotating axles and coned wheelsets, I was always intrigued by the fact that the majority of NCB underground vehicles had fixed axles with the wheels rotating independently of them. Even though they had tapered wheelsets, the lack of coupling of the wheels effectively eliminates any self steering or centralising element. Underground manriding trains may not have been high speed but the system was perfectly adequate for speeds up to 25 mph and around sharp curves (not together!) on 3'-0" and 2'-6" gauge. It would have been good to have done some instrumented testing but, to the best of my knowledge, this was never done.
I would presume that the curves on mine tramways were *so* sharp that the differential effect from coning the wheelsets would have provided nowhere near enough compensation for them, so wheels rotating freely on the axle were seen as the best choice in those circumstances.
That's a very interesting example and obviously it was well tried and tested, but there cannot be much if any differential effect, or self-steering with a conventional coned wheelset, because it is constrained by the axleboxes in the horns, and has to move in a straight line. If you want proper self-steering you have to do the axleboxes differently, and include some flexibility, and the wheel profile is then very critical.
Then of course there is Hornby Clockwork, with steeply coned wheels with no root radius, free to rotate on the axles, and trains with a high C of G going very fast around sharp curves with no transitions, on rails with a semicircular head profile, without coming to grief. Maybe Mr. Hornby knew a thing or two.
I'm off to the pub....
The contact area ia small even with coning, seehttps://www.facebook.com/photo.php?fbid=10155707631041338&set=a.471961461337&type=3&eid=ARByK4LPQAsabf8saw4F0fNKfYWAaZo-744baCJbvnJEwZSGilfJ8beGRn5JsiIS6mocnQpLjn3cByc9
My father was given a 5" gauge bogie chassis for a riding trolley which he completed and used. I cannot be certain that the wheels were coned but I think they were. The axle boxes had rollers on the top so they could rotate in the the bogie frames to allow some self steering. The bogies also had tapered rollers between the bolster and the stretcher so the whole bogie could rotate easily. After this trolley had been in use for a while it developed a tendency to hunt at a specific speed on straight track. It appeared that the wheel sets were moving from side to side until the flange radii came against the rail head. My Father retyred the wheels giving less side to side clearance and modified the axle boxes to elimnate the self steering. After this the trolley was fine and is still in use after more than 40 years.
For those who are interested, Darlington plus Altoona can be found in more detail in the March 16th 1939 edition of The Model Engineer, Issue no. 1975. The cover has several fast boats in echelon. LBSC describes it as a "naturalised" Pennsylvania E6 atlantic.
I heartily recommended the following Model Engineer index website for finding particular articles/issues of interest.
Thanks for the reference - I had that issue of ME until a recent clearout. I wonder how many other LBSC locos of that period are still around.
I am sure that many of the locos are still around. The 2 1/2" gauge society now own the original Ayesha and have run it in recent years. I know that at least 3 of his own locos are in private hands within 15 miles of my home.
For information, Camden Miniature Steam Services offer a digital version of LBSC his life and locomotives by Brian Hollingsworth.
I've got one of LBSC's here, and there is another less than 10 miles away.
Are we allowed to ask for some more info on what you’ve got?
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I have to admit that my question was a bit loaded, as I have two of his locos.
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