Wheels video

[andyhigham]

Interesting video


youtu.be/XzgryPhtc1Y

[Jock McFarlane]

Jan 3, 2022 19:39:59 GMT andyhigham said:

Interesting video


youtu.be/XzgryPhtc1Y

Fascinating video and confirms what I always thought;  the coned shape is to keep the wheels central on the track.  However, I am not convinced that the cone compensates fully for the effect of curves other than very gentle curves. One day I will wrap  a wet towel round my head and attempt the maths for different radii !

Regards

JM

[andyhigham]

Ride on the London underground sardine can. Gentle curves are relatively silent, the tighter curves cause howling from the wheels. I guess the limit of the differential effect is somewhere between the two

[Neale]

Anyone remember the London Science Museum, in the children's section? There was a length of rail, arranged to slope downwards with a curve towards the bottom, and three sets of wheels - coned conventionally, parallel, and coned the wrong way. I spent quite a lot of time playing with that and observing the action!

But back to the video - I have always thought that the self-centring action on straight track was down to what they call "differential action", that is, if the wheel set moves sideways, the effective wheel diameters and hence circumferences are different. One wheel therefore travels further than the other so the wheelset tends to twist in such a way that it moves back towards the centre of the track. However, it will inevitably overshoot until it is offset to the other side, when it turns back and the cycle repeats. So it doesn't actually settle in the middle of the track but hunts from side to side. I don't know if this is damped in the real world to help centring, or if there is something a bit more subtle about wheel and rail profiles? The video's chat about forces may well also be true, and the two things are merely different ways of looking at it.

Oh, and why is the video in the last clip (DB train) apparently a mirror-image? Did the guy putting the clips together do this for aesthetic reasons without noticing that there was text on the side and front of the loco?

[ettingtonliam]

Do we know who came up with the idea of coning full size wheels, and when it came into general use?

[Neale]

I keep musing on this subject... Couple of questions come to mind.

- Does the amount of coning vary depending on the radius of curves to go round, and if so, by how much? I think I know the theoretical answer to this one.

- These demos and explanations assume a freely-pivoted wheelset. What happens in a bogie, or the fixed wheelbase of, say, an 0-6-0?

That's enough to keep me awake in the small hours!

[jackrae]

For some time at the club I was once a member of, we had derailing problems with bogies comprising coned wheels fitted with ball races and running free on fixed shafts.

I put the argument that this arrangement did not permit self centring and what was required was coned wheels fixed to a rotating shaft.

By way of proving the point I did a demo using a single shaft with fixed coned wheels. Track comprised 660feet of 7.25" irregular oval manufactured from 3/4 x 3/8 flat bar.

I 'launched' the wheel-set by literally throwing it down the track. A couple of minutes later it returned to the starting point, having travelled round the full length of the track, steering itself round the curves without incident.

I feel that convinced the members that fixed coned wheel-sets do work, even at model scale

With respect to Neale's question, the axle pitch length of the 0-6-0 arrangement is very much shorter than the radius of the curves and some transverse float of the axles will permit differential action.

[Gary L]

Jan 3, 2022 22:25:44 GMT Neale said:

I keep musing on this subject... Couple of questions come to mind.

- Does the amount of coning vary depending on the radius of curves to go round, and if so, by how much? I think I know the theoretical answer to this one.

- These demos and explanations assume a freely-pivoted wheelset. What happens in a bogie, or the fixed wheelbase of, say, an 0-6-0?

That's enough to keep me awake in the small hours!

David Hudson summarised the science in a series on Self-steering bogies in Model Engineer several decades ago. You are asking the right questions, in that the conical theory explained in the video is an oversimplification, because the demo features an axle radial to the curve, whereas in conventional railway chassis (using horns) the axles of the wheels that are responsible for curving can never be truly radial (think about it). Also, the straight coning is prone to produce undesirable hunting at high speed, which it was safety-critical to prevent. Some very clever engineers at Derby in the 1950s built on an idea by Prof Heumann which solved the issue by making the coning a compound curve rather than straight, and allowing the axles to float to some extent.

We don’t need to know this for building steam locos; suffice to say that 2 to 3 degrees coning is important for good behaviour on the track, combined with a decent flange root radius. We don’t need to redesign the wheel (literally), because the modern standards for each model gauge have done this for us; just ignore what LBSC and Martin Evans drew, and follow the latest standards instead.

But for the record, if you want something a bit more radical, David Hudson’s design for self-steering bogies works extremely well, and has been in use at our club for more than 20 years. But that’s another story.

This has been covered in this forum before at some length, so let’s not reopen it all over again.

Gary

[Gary L]

Jan 3, 2022 21:02:13 GMT andyhigham said:

Ride on the London underground sardine can. Gentle curves are relatively silent, the tighter curves cause howling from the wheels. I guess the limit of the differential effect is somewhere between the two

Hi Andy

The howling is often associated with flange contact, which occurs when the differential effect runs out (so to speak). It is very undesirable, because it can lead to ‘flange climbing’ and derailment. This is why sharp curves on the mainline are fitted with continuous check rails. It is also, incidentally, why the flange angle is very important too, to keep the tip of the flange well away from the railhead even on the tightest curves. As I understand it, the cone angle of the tread is something of a compromise, with steeper angles (3 degrees or thereabouts) being more suitable for tightly curved lines (like miniature railways) whereas the mainline would be nearer 2 degrees. However the corrections it induces at very high speeds can be uncomfortable or even dangerous, so on the Japanese bullet trains (where curvature was kept very moderate) the engineers found a shallower angle was beneficial to stability. Modern thinking is for a compound cone (see previous answer) which gives a progressive feedback instead of linear to this correction mechanism, but this is very difficult to reproduce on a non-CNC lathe, and of lesser value on a traditional railway chassis (though I believe Railtrack require it nowadays even on steam locos running on the mainline).

Gary

[uuu]

Readers who want to play with numerical modelling of the issue might like to read this paper, presented to the 6th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems in 2003: Link to article

Wilf

[ettingtonliam]

OK, but back to a question I asked earlier. Who is thought to have come up with the idea of coned wheels, and when did it come into general use?

[andyhigham]

My question is are the non flanged wheels on the 9F coned or parallel?

[uuu]

Jan 5, 2022 13:52:04 GMT ettingtonliam said:

OK, but back to a question I asked earlier. Who is thought to have come up with the idea of coned wheels, and when did it come into general use?

I've found this paper, which suggests "coning was well established by 1821", with George Stevenson referring to it in a paper. Von Oeynhausen refers in a paper of 1826. It's noted also that earlier (1735) cast iron wheels had coned treads, because of foundry practice (presumably to allow the pattern to b removed from the mould). Brunel describes how the flanges of wheels should not contact the rails in normal motion, in 1838.

Link to paper The dynamics of railway vehicles

Wilf

[stevep]

Jan 5, 2022 14:14:31 GMT andyhigham said:

My question is are the non flanged wheels on the 9F coned or parallel?

I suspect that they must be coned, as the rails also lean inwards, offering maximum contact to the coned wheels.

[don9f]

Jan 5, 2022 15:21:12 GMT stevep said:

Jan 5, 2022 14:14:31 GMT andyhigham said:

My question is are the non flanged wheels on the 9F coned or parallel?

I suspect that they must be coned, as the rails also lean inwards, offering maximum contact to the coned wheels.

This has cropped up before and as far as I know, they were coned when the 9F was first introduced, with the same angle etc. as the other driving wheels, but after the tendency for the flangeless wheels to derail on poorly maintained track became obvious, the profile was changed to one with a parallel section in the centre of the tyre (about a third of it) and angled (or coned) sections either side of this, plus the usual chamfers at front & back edges of the tyre. This was known as the BR “X” profile and presumably gave these wheels a better chance of rerailng themselves.
The tyres of the flangeless wheels were slightly wider than those of the other wheels, but I don't know if they were like this originally or a later modification.

Cheers   Don

[don9f]

Unfortunately I don’t have a good photo of a flangeless wheel and although I have “lightened” it up a bit you still can’t see the profile well in this one of 92214 on its “Gauging run” after arrival at the East Lancs Railway in 2005. It’s moving through a curve of nominal 5 3/4 chains radius of well maintained track....but you can see just how much the flangeless wheel moves across the railhead.
It did derail and rerail itself once on one of the curves in the loco shed yard whilst it was there!



Cheers Don

[lesstoneuk]

Jan 5, 2022 14:14:31 GMT andyhigham said:

My question is are the non flanged wheels on the 9F coned or parallel?

From what I can remember, when "Evening Star" was at Didcot, the flange less wheel was parallel.
You must all take into account that at some point on a curve, one of the wheels on an axle has to slip. The coning will not be enough to accommodate the difference in length of the inner and outer rails. In all likelehood, it will be the inner wheel due to altered weight distribution caused by centrifugal force.

[Gary L]

Jan 7, 2022 1:18:39 GMT lesstoneuk said:

Jan 5, 2022 14:14:31 GMT andyhigham said:

My question is are the non flanged wheels on the 9F coned or parallel?

From what I can remember, when "Evening Star" was at Didcot, the flange less wheel was parallel.
You must all take into account that at some point on a curve, one of the wheels on an axle has to slip. The coning will not be enough to accommodate the difference in length of the inner and outer rails. In all likelehood, it will be the inner wheel due to altered weight distribution caused by centrifugal force.

...and parallel treads always must slip except on dead straight track. But you raise a question which shows how the coned wheel principle (demo'd in the video at the head of this thread) is true, but an oversimplification. The leading and trailing drivers on the 9F adopt the position on the track where the differential effect of coning forces them to go. But driving axles 2 and 4 cannot do this, except to the extent that any endfloat allows them to move sideways. The centre axle is even more disadvantaged, so coning its wheels is probably pointless, except to try and get a line contact with the railhead instead of a point loading. The suspension will accommodate the height difference on a curve, but the theoretical differential effect is not possible.

And yet, like the bumble bee which the theory said should not be able to fly*, the 9F was an efficient and useful machine, as were the other 2-10-0s and 2-8-0s, and little troubled by slipping AFAIK. Nevertheless, you would expect (from theory) that the 9F would have a greater tendency to initiate a slip on curved track rather than straight, with the middle drivers breaking away first. I've no idea if this was the case!

Gary

(*no longer true, but still often quoted!)

[oldnorton]

Jan 3, 2022 22:12:12 GMT ettingtonliam said:

Do we know who came up with the idea of coning full size wheels, and when it came into general use?

No one wants to answer your question   but I think it is a good one.

Let's speculate. The earliest engines, around 1830-40, were 0-4-0s and as they tried to travel faster must have ricocheted all across the track. The need to devise a stabilising effect might have developed this early, and it's inventor might be undocumented?

Norm

[ettingtonliam]

Locomotion was slightly earlier, 1825, and was originally fitted with spoked wheels, but these failed regularly. Timothy Hackworth. who maintained the locos at Shildon fitted cast iron 'plug' wheels, of the type which Locomotion still has today. Owing to limitations in foundry and machine shop capacity, these were in 2 parts, an inner ring which was bored for and keyed to the axle, and an outer ring which was secured to the inner ring, by a series of wooden wedges, and which incorporated the tread and the flange. 2 Prussion engineers visited the S&D in 1827, and inspected Locomotion, or one of its 3 close siblings, noting (without further comment) that the tread was 4 1/6" wide and was conical tapering 1/6" towards the front. Now, its is known that Hackworth at this point didn't have a lathe big enough to turn wheels of 4 foot or so in diameter, so the tread would have been 'as cast', and so very likely to have been tapered due to the 'draw' necessary to withdraw the wheel pattern from the sand mould.

At what point, when wheels were machined on the treads, someone noticed that a turned parallel tread hunted more than its as cast predecessor, and realised why, I don't know.

Bear in mind that Locomotion travelled at between 5 and 8 mph and was pretty lively vertically due to the cylinder arrangement, Hackworth et al might not have paid too much attention to a bit of 'hunting'