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Post by chris vine on Dec 15, 2018 10:51:16 GMT
Hi Alan,
Your point about angling in the rails may be true, however, the reduction of friction because of the nearly point/line contact is quite small. Even with just a very thin line of contact, IE tapered wheel running on a sharp corner of the rail, there will still be lots of friction.
If there is oil on the rail/wheel, then the very small contact will probably increase the friction (compared to the bigger contact area if all is set exactly correct) because the wheel will cut through the oil film!
All model rails that I have seen are rounded on the top running surface, as in hot rolled mild steel, or the lovely profiled rails.
Chris.
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jackrae
Elder Statesman
Posts: 1,333
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Post by jackrae on Dec 15, 2018 13:51:49 GMT
Taking the coning versus not coning argument to its physical limits, we have two example situations
a) a single sphere of say 3 times the diameter of the track gauge as representative of coning b) a cylindrical bar of the same diameter as representing non-coning
If both are given a shove down the track there are no prizes for guessing the outcome
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Post by delaplume on Dec 15, 2018 13:52:42 GMT
The problem with coning your model wheels is that the club track that you are running on must also have inclined rails to match your coning...... If not then you have a parallel tread sitting on an angled rail which gives you a line contact---- ie no power transmission at all..( or braking for that matter !! ). How many club tracks use rectangular section steel bar for rail--- held vertically ??......... .or more up to date}-- use Vignoles section Aluminium rail held vertically ?? If you look at the end of black flat bat it's not square on the short side thet the wheels run on so the tapered wheel works better than a parallel wheel. Jason True -- it's not square, but neither is it tapered correctly either....Sorry Jason but you seem to be missing the point.......Rail chairs are made ( cast ) with the 2 degree taper built into them such that the whole rail is tilted inwards.......This now matches the cone on the wheel tread and gives the effects already mentioned..........There seems to be an "Urban myth" among some that it's the head of the rail that's tilted ---not so !! A few years ago my late friend Roy and I were running his 5" Simplex ( Parallel tread ) at our club track at Rugeley ( Rectangular steel bar, mounted vertically ) ... Our normal train was 2 x 7.25"g. trucks with 10 adults and an up incline of 100 feet .......No problems--we ran all day....The Simplex cab was "open" ie}--- we could see the rear end of the rear wheels and they were the usual dull, grey colour..... The following weekend we took the same Simplex down to the big International meeting at Guildford where we barely managed one full lap with just a Driver and the driving truck--- slipping and no traction !!......... And crucially there was a thin Black line on both driver wheel treads just away from the root radius..... We asked a club official who confirmed that the rail was indeed inclined inwards..........One week-end wasted !! ( apart from the Hog Roast and Beer that is -- yummy !!)... Quite simply put, there must be FULL CONTACT between the railhead and the wheel tread ----- irrespective if coned or parallel ----- for full traction to take place....
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Post by delaplume on Dec 15, 2018 14:08:56 GMT
That's interesting as Grandad's Britannia also has a single loose wheel, in this case on the rear axle, right hand side. Most likely press fit so it was probably the largest tolerance of the set. Parallel tread and mostly run on steel bar raised track. Regards, Dan A moved wheel on a Britannia? Just like the real thing, then! ---- but that was found to be due to the use of hollow axles, the wrong fitting tolerances and -- I think ---wrong sequence used when assembling ... "Standard locomotives temporarily withdrawn". The Railway Magazine. Vol. 97 no. 608. December 1951. p. 856.
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Dec 15, 2018 14:23:45 GMT
Hi Alan, Your point about angling in the rails may be true, however, the reduction of friction because of the nearly point/line contact is quite small. Even with just a very thin line of contact, IE tapered wheel running on a sharp corner of the rail, there will still be lots of friction. If there is oil on the rail/wheel, then the very small contact will probably increase the friction (compared to the bigger contact area if all is set exactly correct) because the wheel will cut through the oil film! All model rails that I have seen are rounded on the top running surface, as in hot rolled mild steel, or the lovely profiled rails. Chris. If I may butt in, it is even a little more complex than that Chris. I would recommend reading David Hudson's series of articles in ME Feb-Aug 2003, where (amongst other things) he explains the effect of elasticity of both rail and wheel on rolling resistance. At a more practical level, the usual purpose of coning is 'self centring' as distinct from the 'self steering' action I referred to earlier. The worst friction by far, occurs when the flange makes contact with the railhead, and the object of coning is to prevent this, which it has been doing successfully for well over a century and a half. Our experience of many years with the quite steeply-coned tyres of our self-steering bogies is that it is not necessary (though desirable certainly) to have matching inclination of the railhead. A lot of our track is upright flat bar, but it does not cause problems with the 3 degree++ coned steel wheels of our passenger cars. We refurbished our earliest self-steerers recently after 10 years heavy service, and the wheels were almost as good as new; it was not necessary to reprofile them. As Hudson's articles show, you never get true point or line contact, because of the elastic deformation of the metal as the wheels travel. This is particularly true when heavily loaded, as is generally the case with passenger cars. Best regards Gary
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Post by delaplume on Dec 15, 2018 14:44:12 GMT
Hi Gary----
I'm now going to appear to "shoot myself in the foot" by saying that the upright steel bar rail allied to a coned passenger truck wheel is precisely what you DO want as it gives a much-reduced rolling resistance .... My point earlier was to do with loco power transmission / braking effects..
Quote}--"because of the elastic deformation of the metal as the wheels travel" So, does that mean Mallard is actually the fastest Uphill locomotive in the world ??...technically that is !!!...
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Neale
Part of the e-furniture
5" Black 5 just started
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Post by Neale on Dec 15, 2018 16:13:01 GMT
There are also a number of different circumstances to take into account, and the same answer might not apply in all cases. Or maybe it does - I'm still not quite sure!
D&C wheels - must transmit power, therefore need frictional grip which is more important that low rolling resistance. Must also be fitted solidly to axle to maintain quartering (thirding, etc).
Tender wheels - relatively long rigid wheelbase, ideally want low rolling resistance but really not concerned about grip. Same might be true of 4-wheel driving trolley but which carries more weight.
Passenger car bogie - short wheelbase, low rolling resistance wanted, don't care about grip, must also be able to support considerable loads - more than a loco?
Loco leading bogie - short wheelbase, but want self-steering/centring(?) effect to assist loco into curves.
Conclusion - the fact that a particular track profile/wheel profile combination does or does not work well for a loco says nothing about tender/passenger bogie requirements which might be different.
I've only really been familiar with two tracks. One was 40+ years ago at Worcester, where I seem to remember that the track was rolled steel bar held together with turned spacers and bolts, therefore upright. My current club track, Newton Abbot, uses rolled steel bar in plastic sleepers, but as far as I know these are also upright. The Worcester track used to have fairly heavily loaded trains on public running days and I don't remember much of a problem. No idea of wheel profiles used. My current club does not do public running so trains are much more lightly loaded, so I don't think that produces any useful data.
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don9f
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Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
Posts: 960
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Post by don9f on Dec 15, 2018 18:00:39 GMT
Hi Neale if it’s any help, despite the problems I had with my own loco, I would still recommend you fit your tender wheels securely to their axles. Allow some end float, cone the wheeltreads at 3 degrees and I’m sure you’ll be fine.
Cheers Don
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Neale
Part of the e-furniture
5" Black 5 just started
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Post by Neale on Dec 15, 2018 21:29:28 GMT
Sorry, Don - too late!
Well, actually, my wheels are already turned with 3deg coning, there is a little bit of endfloat built in (or will be by the time the horns and axleboxes are fitted but that is what they are machined to achieve) and I already have the Loctite to glue wheels to axles. Advice taken in advance of actually receiving it!
But it's good to know that there are others that think that way as well. I still think that it's an interesting issue that has thrown up some useful discussion and insight. For example, what I have just realised is that while coning on a long-wheelbase vehicle like a tender sounds like the right thing to do, its effect in terms of steering and self-centring is limited by the fact that the axles are not free to swivel, so typically front and rear axles of a 3-axle tender cannot be radial to the curve, or oscillate about that position, as they are rigidly held in that plane by the axleboxes/horns. There must be some slip in at least two of the wheelsets (probably front and rear). The video clip of a coned shaft shows how, to self-steer, the axle moves in front of and behind the radius of the bend as part of its overshoot/correction mechanism. Classic second-order feedback system with no damping? I wonder if that's why getting the coning right can be so effective on passenger bogie wheels where the axles can stay more closely to radial on curves?
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don9f
Statesman
Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
Posts: 960
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Post by don9f on Dec 15, 2018 22:19:15 GMT
Earlier today I was rummaging about in some photos, looking for something unrelated to this particular thread and found a series of shots taken during the "Gauging Run" of 92214 after its arrival at the East Lancs Railway in 2005. Here are three of them that may be of interest and show something of what you have just talked about above. This particular checkrailed curve was (maybe still is?) pretty tight at a minimum calculated 5 3/4 chains radius. Admittedly its only this tight over a short distance but it was where the outer track of the curve at Bury South "tightened up" to the points connecting it to the Single Line. You can see in the third photo how the wheelsets took up their positions on the curve (with a lot of graunching noises, not so bad when it was raining). Note the positions of the various wheels related to the rail and that the centre flangeless tread has started to move off the railhead....the checkrail is no help to this one! This is ok on well maintained track, but with loose fixings, rotting sleepers, gauge spread etc. it would be down the inside of the outer rail and busting the track open for the wheels that follow! The axles obviously remain parallel to each other, all the lateral play is taken up and a certain amount of “crabbing” has to take place to get it round the curve. Cheers Don
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Post by delaplume on Dec 16, 2018 0:31:43 GMT
Hi Don,
I hope those bruises on your head have gone down now --LoL !
Yes, you can quite clearly see the dispositon of the different wheel sets........
Couple of questions for you if I may}----
a) Interesting arrangement of spring clips in the chairs --- any idea what that's all about ??
b) Lovely, crisp images with good depth of focus---What camera do you use ??
Finally I know that the Orange colour coded overalls are Hi-Vis but what's the Red and Purple ones signify ??...
Cheers
Alan
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Dec 16, 2018 1:31:47 GMT
Hi Gary---- I'm now going to appear to "shoot myself in the foot" by saying that the upright steel bar rail allied to a coned passenger truck wheel is precisely what you DO want as it gives a much-reduced rolling resistance .... My point earlier was to do with loco power transmission / braking effects.. Hi Alan Yes, I think the first statement may be true, but it worries some people because it seems "wrong". Our experience over 10 years suggests that the worries are misplaced, but we won't convince everyone. Yes too, the second statement was in my mind as I wrote, but I didn't particularly want to get into anecdotal territory. The trouble is, I don't dispute the experience you have related, but logically I should expect to see the same effect when the factors are reversed; i.e. with upright steel bar rail and coned wheels I should get spectacular slip when Bridget starts up, but I don't. She is relatively light weight, big cylinders, high pressure, and has a trailing carrying axle that unloads the rear driver significantly, so all the secondary conditions are present. OK, I can make her slip easily enough by being clumsy with the regulator, but that isn't by any means the normal style of progress. So there must be other factors in play as well, which I could only guess at. Quote}--"because of the elastic deformation of the metal as the wheels travel" So, does that mean Mallard is actually the fastest Uphill locomotive in the world ??...technically that is !!!... Haha! I seem to recall hearing that the Mallard speed record was on a slightly downhill gradient. But joking aside, as you clearly know, all rail vehicles are indeed (sort of) travelling slightly uphill on level track, though it seems counter-intuitive. Best regards Gary
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Gary L
Elder Statesman
Posts: 1,208
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Post by Gary L on Dec 16, 2018 2:13:46 GMT
Sorry, Don - too late! Well, actually, my wheels are already turned with 3deg coning, there is a little bit of endfloat built in (or will be by the time the horns and axleboxes are fitted but that is what they are machined to achieve) and I already have the Loctite to glue wheels to axles. Advice taken in advance of actually receiving it! But it's good to know that there are others that think that way as well. I still think that it's an interesting issue that has thrown up some useful discussion and insight. For example, what I have just realised is that while coning on a long-wheelbase vehicle like a tender sounds like the right thing to do, its effect in terms of steering and self-centring is limited by the fact that the axles are not free to swivel, so typically front and rear axles of a 3-axle tender cannot be radial to the curve, or oscillate about that position, as they are rigidly held in that plane by the axleboxes/horns. There must be some slip in at least two of the wheelsets (probably front and rear). The video clip of a coned shaft shows how, to self-steer, the axle moves in front of and behind the radius of the bend as part of its overshoot/correction mechanism. Classic second-order feedback system with no damping? I wonder if that's why getting the coning right can be so effective on passenger bogie wheels where the axles can stay more closely to radial on curves? Hi Neale You are right in almost every detail. You cannot get "self steering" unless the axles are free (and I mean free) to take up a position radial to the curve. Some modern bogie designs achieve this, but it cannot be done with conventional axles constrained by horn blocks. So the video clip is indeed slightly misleading, because the coned shaft plainly is free to take up a radial position and manifestly self-steers as a result (which makes it a good illustration of the benefits of a truly self-steering suspension system). Your tender will not (and cannot) self-steer, but by coning the wheels as you have done, it will self-centre, and that will be enough to stop the ill-effects that have been described. The detail that may not be correct is 'There must be some slip in at least two of the wheelsets'. A three-axle tender is rather a complex system to be dogmatic about, but we are back to the matter of the differential diameters of coned wheel sets being there not only to self-centre the wheels on straight track, but also to remove the need for slip on curves, or at least on curves of radius large enough to avoid flange contact. My guess is that the centre axle of a three-wheel tender probably does slip on curves, once any available side-play has been taken up. What is very clear though, is that if the rear axle is not coned, then on curves something has to give. The 'something' might be tread slip, unless you inhibit this by plonking the weight of a hefty driver on top. At this point, the next 'something' is quite likely to be the joint between the axle and one or other of the wheels, which is where this thread started... -Gary PS. 'Classic second-order feedback system with no damping' -Yes indeed! This is why the self-steering wheel profile has compound coning. It is also the reason for the observation in early BR days that the rough riding and 'hunting' of the early Mark 1 carriage bogies was much reduced once the wheels had worn to a concave cone profile. The so-called 'worn wheel profile' was developed from this and standardised. Actually BR had rediscovered an observation from much earlier in Germany, but that's another story.
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Post by chris vine on Dec 16, 2018 10:10:01 GMT
Re Mallard (and all trains) going up hill:
Yes the fronts (leading contact patch) of the wheels are going up hill, but the rear/trailing part of the wheel is going downhill!!
Chris.
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Post by Rob on Dec 16, 2018 11:00:48 GMT
Earlier today I was rummaging about in some photos, looking for something unrelated to this particular thread and found a series of shots taken during the "Gauging Run" of 92214 after its arrival at the East Lancs Railway in 2005. Here are three of them that may be of interest and show something of what you have just talked about above. This particular checkrailed curve was (maybe still is?) pretty tight at a minimum calculated 5 3/4 chains radius. Admittedly its only this tight over a short distance but it was where the outer track of the curve at Bury South "tightened up" to the points connecting it to the Single Line. You can see in the third photo how the wheelsets took up their positions on the curve (with a lot of graunching noises, not so bad when it was raining). Note the positions of the various wheels related to the rail and that the centre flangeless tread has started to move off the railhead....the checkrail is no help to this one! This is ok on well maintained track, but with loose fixings, rotting sleepers, gauge spread etc. it would be down the inside of the outer rail and busting the track open for the wheels that follow! The axles obviously remain parallel to each other, all the lateral play is taken up and a certain amount of “crabbing” has to take place to get it round the curve. Cheers Don Don, those photos are fantastic - do you have your others anywhere that I can have a look through? Hi Don, Couple of questions for you if I may}---- Finally I know that the Orange colour coded overalls are Hi-Vis but what's the Red and Purple ones signify ??... Cheers Alan Alan, my guess is that the purple overalls are just your standard driver/fireman blue overalls that always seem to have that purple tinge, perhaps because they have been through the wash a few hundred times. You can spot the 'grease top' hat in the first image. As for the red overalls - might just be a standard pair of 'Dickies' in red.
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don9f
Statesman
Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
Posts: 960
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Post by don9f on Dec 16, 2018 17:52:26 GMT
Hi, glad you like the photos....a few questions answered and some additional info:-
As stated, these photos were taken in 2005....before I used such things as a phone, or an Ipad to take them. I still have the camera but don’t use it any more....it is a “Canon 350D” with an 18-55mm zoom lens. I used Photoshop last night to reduce the file size for uploading to Imgur.
I don’t know why the rail clips are orientated the way they are but I think that point had recently been moved nearer to the bridge, following a derailment of a passenger train on that curve (was it 5690 Leander)? Maybe it’s something to do with the repairs after that, or to help keep the track to gauge?
At the time I was the Lead Engineer for the owning Trust of the loco, so had a keen interest in how it performed and how it was looked after and on this occasion, the loco was being driven by the East Lancs’ full time fitter and the chap in red overalls was one of his regular mates. Some people don’t appreciate that red shouldn’t be worn on or around the track but.....
The chap in “purple” was the East Lancs CME and as posted above, it’s what sometimes happens to overalls after lots of washing!
The orange fellas were P. Way dept.
Much later in its stay at the ELR it derailed the RH centre driver on some knackered pointwork in the loco shed yard, but managed to rerail itself a bit further on.
Prior to this it had similarly derailed on dodgy pointwork at Barrow Hill but had to be rerailed with jacks etc., so you can fully understand their reputation for finding weaknesses in poor track!
Finally I forgot to mention that you can appreciate from the photos how the pony truck has moved well over and it’s side-control springs would really be helping guide the front of the loco round the curve....note the back of it’s RH flange hard up against the checkrail.
Cheers Don
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don9f
Statesman
Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
Posts: 960
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Post by don9f on Dec 16, 2018 18:05:32 GMT
Rob....PM sent
Don
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Post by delaplume on Dec 16, 2018 18:24:55 GMT
Thanks Don---Much appreciated... This is what hangs above my TV set }----------> -------------->
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don9f
Statesman
Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
Posts: 960
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Post by don9f on Dec 16, 2018 18:33:37 GMT
👍
Sorry was wrong about it being a Nikon camera, it was before that.... a Canon (edited).
Don
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Post by dhamblin on Dec 16, 2018 21:38:24 GMT
The horizontal clips are Panlock type, which provide more resistance to coming loose in the chair compared with the traditional vertical type. Pretty sure these are used on LU for all main line BH rail and where rail is renewed in depots / yards.
Regards,
Dan
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