Engineering, Injuneering and Knitting

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Engineering, Injuneering and Knitting

Postby Proto87stores » Sat Dec 16, 2017 3:17 pm

I was struck by the recent reference to reading prototype engineering drawings as being the necessary way source of information for scaled-down working model kit building.

Clearly it is rarely possible to build an exact working model by merely scaling down the individual parts of a full size prototype. By the time the scale difference is as much as 1:76, the issues with motion clearances, weight, strength of materials, etc., become such that an alternative method of simulating the workings is the small scale is needed. An obvious example for P4 is replacing a working boiler and steam cylinders with an internal electric motor and axle drive gearbox.

The job of the kit designer is to interpret the original drawings, plus, photos, experience and full understanding, as to how the model should appear to work, then KNOWLEDGEABLY AND PROPERLY RE-ENGINEER the mechanism of the model and its parts to provide the necessary simulation of the original working functionality in a reliable, lasting, and practical kit-buildable way. Given reasonable instructions of how to assemble the revised mechanism, I fail to see the need for any reference to the original drawings, except perhaps for placement of the finer cosmetic details.

Attempting to replace the mechanism aspects by merely scaling down the original parts and/or method, with revised clearances, in the hope that it will work well enough, or relying on incredible craftsmanship skill by the kit builder is not a substitute for engineering a proper solution. In the event that that kit provider accepts that the kit may be modified by the builder, or, for example, as a chassis, be available to be incorporated into other models then an explanation of the critical aspects of why and how the new mechanism functions should be provided.

Andy

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Re: Engineering, Injuneering and Knitting

Postby Julian Roberts » Sun Dec 17, 2017 11:06 pm

Well Andy I think I know where you saw that. Here is the first full page of Iain Rice's book on Chassis Construction which as always with him puts the issues in a way comprehensible to the averagely keen but non scientifically trained enthusiast - as is he, being, I believe, qualified at Art College. Hopefully Wild Swan will forgive any breach of copyright. I assure anyone that the rest of the book is equally stimulating.

Fraid I haven't got the knack of rotating photos here. This was the right way up at home!

20171125_224615.jpg
It is readable if you can enlarge and re-orientate it

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Re: Engineering, Injuneering and Knitting

Postby John Bateson » Mon Dec 18, 2017 9:42 am

Dare I question the assertion from the young Mr Rice that steam engines get round bends by bending?
While there must be some degree of bend within any framework, which may or may not help, I have always held the view that steam engines get round bends because of the equation noted in the Society Digest that TG(min)>BB(max) + 2EF(max) which allows the engineers here to play with versine calculations and is also the reason that while a dock tank may get round a 2.5 chain radius in Connah's Quay, a GWR King will need 8 chains and will not bend enough to get into these same docks.
I realise this is an extreme (reductio ad absurdum) argument and apologise for taking the discussion into the realms of fantasy, but the principle must apply that the main reason steam engines get around bends is down to the equation above , the difference between TG and the sum of the locomotive parts. Of course the rails and loco parts will wear in time and make the curve taking easier, but the King will still not get into Connah's Quay docks!

Parapet ready to duck behind, steel hat on.

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Re: Engineering, Injuneering and Knitting

Postby billbedford » Mon Dec 18, 2017 10:00 am

I have a friend who used to be an art teacher. She used to tell me that she could persuade her students to believe any sort of rubbish, as long as she said it with enough conviction.

I believe that Rice, and Sharman, have the same 'gift'. Just because something is written by a 'guru' doesn't mean you have to suspend your critical faculties.
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Re: Engineering, Injuneering and Knitting

Postby Andy W » Mon Dec 18, 2017 10:08 am

Sounds like most politicians Bill.
Make Worcestershire great again.
Build a wall along the Herefordshire border and make them pay for it.

Proto87stores

Re: Engineering, Injuneering and Knitting

Postby Proto87stores » Mon Dec 18, 2017 3:07 pm

billbedford wrote:I have a friend who used to be an art teacher. She used to tell me that she could persuade her students to believe any sort of rubbish, as long as she said it with enough conviction.

I believe that Rice, and Sharman, have the same 'gift'. Just because something is written by a 'guru' doesn't mean you have to suspend your critical faculties.


Errr, The quoted article was by Iain Rice.

What is the technical basis on which you added in Mike Sharman's name Bill?

Andy

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Re: Engineering, Injuneering and Knitting

Postby Julian Roberts » Mon Dec 18, 2017 5:01 pm

Equally, just because something is written by a 'guru' (or an artist) doesn't mean it isn't true. The more popular the politician, the more suspicious we should be, and vice versa, IMHO.

I put the page there not because I agree with every word but because it makes the general point that things behave differently in 4mm scale to the real thing, so "Scale It Down Regardless" doesn't work in practice, and a model may need different engineering solutions, which was Andy's general point.

I agree that the loco on the curve is not a convincing example. Andrew Jukes makes the case clearer when he says that a scale 60' piece of rail behaves completely differently when suspended by a model crane to the way a real piece of rail does - the latter sags while the former does not. Imagine a 600 foot long train carrying lengths of single welded rails in P4 or 00 for that matter snaking round curves...? - and yes I know the model rail web is thicker than it should be, but doubt rail with scale web would be able to perform that trick.

Meanwhile, while I'm sure John is right, the TGmin is subject to the famous Gauge Widening of this parish depending on the radius. Didn't all locos have a specified minimum radius?

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Re: Engineering, Injuneering and Knitting

Postby Le Corbusier » Mon Dec 18, 2017 5:13 pm

a thing I have always been curious about chez Rice is to do with suspension. Iain suggests (I think in his track work book but could be the chassis one) that on the real thing the track itself sinks in to the ballast as the train rolls over providing a degree of 'suspension'. This as I recall went alongside his theories of the flexure within the main frames from side to side.
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Re: Engineering, Injuneering and Knitting

Postby Paul Townsend » Mon Dec 18, 2017 5:20 pm

Le Corbusier wrote:a thing I have always been curious about chez Rice is to do with suspension. Iain suggests (I think in his track work book but could be the chassis one) that on the real thing the track itself sinks in to the ballast as the train rolls over providing a degree of 'suspension'. This as I recall went alongside his theories of the flexure within the main frames from side to side.


Put yourself in the cess when a steam loco goes past. If the track is bullhead and chairs on wooden sleepers, it certainly goes up and down. I have not measured this but it looks like at least an inch for a big loco. I suspect more modern track is stiffer.

Having never put my head inside travelling mainframes I can't comment on that sideways flexure.

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Re: Engineering, Injuneering and Knitting

Postby billbedford » Mon Dec 18, 2017 5:36 pm

Le Corbusier wrote:a thing I have always been curious about chez Rice is to do with suspension. Iain suggests (I think in his track work book but could be the chassis one) that on the real thing the track itself sinks in to the ballast as the train rolls over providing a degree of 'suspension'. This as I recall went alongside his theories of the flexure within the main frames from side to side.


Then you should ask yourself what is actually compressing, and where is the resilience coming from.
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Re: Engineering, Injuneering and Knitting

Postby Philip Hall » Mon Dec 18, 2017 6:10 pm

I remember train watching at Clapham Junction in steam days and on the up fast line where it ran alongside the central sidings there was a particular rail joint which went up and down two or three inches as a train went over it. I wasn’t looking at the suspension in those days but a combination of factors must have worked because nothing ever came off. True speeds were not high.

Iain and Mike wrote most of what they wrote not from theory but hard headed practice. It wasn’t rubbish propounded by people who wanted to convince others that their chosen methods were better, it was just telling them what had worked in the spirit of helpful information. And having fun. Too many times in this modern world folk are prone to dismiss other’s ways of doing things, which demonstrably do work, on the high altar of ‘this might be better’ or sometimes ‘this is better’. Well I have been using their methods for forty years now and they do work, they continue to do so and I will therefore continue to use them. Yes of course I shall experiment where the fancy takes me but I want to build a large (ish) working model railway in what will be a shorter time that I might have liked were I starting twenty years ago. So I don’t have time not to take some short cuts by sticking to them.

To me the fact that there have been practical people in this wonderful hobby who have been prepared to stick their heads above the parapet and put forward their knowledge and experience is one of the things that encourages me to stick with it. And have fun in the process. And I am conscious that I have just stuck my head above said parapet. But I’m having fun...

Philip
Last edited by Philip Hall on Mon Dec 18, 2017 7:09 pm, edited 9 times in total.

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Re: Engineering, Injuneering and Knitting

Postby Le Corbusier » Mon Dec 18, 2017 6:13 pm

billbedford wrote:
Then you should ask yourself what is actually compressing, and where is the resilience coming from.


Bill,

Given that ( as Paul has observed) the rails do appear to move up and down and not simply down, as you say there must be resilience somewhere in the system. I assume that the ballast itself doesn't have resilience ... as to my knowledge stone has no real elasticity. The rail itself has elasticity, but as it does not leave the sleepers suspended following the compression the effect must be minimal. The sleepers being timber I think would simply crush if the load were sufficient rather than flex. I would therefore assume that it is the ground itself which is providing the resilience (I know with driven piles the impact can be transferred a considerable distance through the ground). So as a guess, firstly the sleepers and then the interlocking ballast spread the impact over a largish area which is then absorbed and dampened by the ground? If this is the case then presumably resilience would be significantly reduced at points were the track runs on a solid rock base such as through a tunnel?
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Re: Engineering, Injuneering and Knitting

Postby John Bateson » Mon Dec 18, 2017 7:17 pm

Didn't all locos have a specified minimum radius?


Probably - yes.

Finding them is another matter. I suppose in theory somebody here with the inclination could derive all these from the wheel diameter and wheel spacing specifications and publish a technical note...
But surely somebody has all this information already tucked up in a spreadsheet somewhere?

John

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Re: Engineering, Injuneering and Knitting

Postby Le Corbusier » Mon Dec 18, 2017 7:48 pm

Julian Roberts wrote:https://m.youtube.com/watch?v=Q3JINX9Gnv0


The rail seems somewhat loose here? ...and the sleepers would appear to have split.

Are you saying that the movement is actually the rail with sleeper attached floating up and down on the ballast .... I am not sure I buy that as the pictures from my period have the ballast packed around the sleepers pretty much flush with the top. If the sleepers floated moving up and down I would have thought there would be a degree of disturbance to the ballast which is not discernible in the photos. Also I would have thought such movement would go through sleepers and fixings pretty rapidly?
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Re: Engineering, Injuneering and Knitting

Postby billbedford » Mon Dec 18, 2017 7:59 pm

Le Corbusier wrote:
Julian Roberts wrote:https://m.youtube.com/watch?v=Q3JINX9Gnv0


The rail seems somewhat loose here? ...and the sleepers would appear to have split.

Are you saying that the movement is actually the rail with sleeper attached floating up and down on the ballast .... I am not sure I buy that as the pictures from my period have the ballast packed around the sleepers pretty much flush with the top. If the sleepers floated moving up and down I would have thought there would be a degree of disturbance to the ballast which is not discernible in the photos. Also I would have thought such movement would go through sleepers and fixings pretty rapidly?


The sleepers are moving relative to the ballast because there is void in the ballast under them. If the resilience came from formation under the ballast the sleepers and ballast would be moving together.
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Re: Engineering, Injuneering and Knitting

Postby Le Corbusier » Mon Dec 18, 2017 8:10 pm

billbedford wrote:
Le Corbusier wrote:
Julian Roberts wrote:https://m.youtube.com/watch?v=Q3JINX9Gnv0


The rail seems somewhat loose here? ...and the sleepers would appear to have split.

Are you saying that the movement is actually the rail with sleeper attached floating up and down on the ballast .... I am not sure I buy that as the pictures from my period have the ballast packed around the sleepers pretty much flush with the top. If the sleepers floated moving up and down I would have thought there would be a degree of disturbance to the ballast which is not discernible in the photos. Also I would have thought such movement would go through sleepers and fixings pretty rapidly?


The sleepers are moving relative to the ballast because there is void in the ballast under them. If the resilience came from formation under the ballast the sleepers and ballast would be moving together.


Yes I can see what is happening on the film .... but I was hypothesising that this was not a desirable state of affairs and perhaps not what should be happening?

I assume that your comment suggests that in fact this is exactly what happens?

This is the type of picture which led to my initial hypothesis. I thought there would be more disturbance with the ballast.
brake van.jpg
Midland compensator.jpg
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Re: Engineering, Injuneering and Knitting

Postby junctionmad » Tue Dec 19, 2017 2:22 am

Paul Townsend wrote:
Le Corbusier wrote:a thing I have always been curious about chez Rice is to do with suspension. Iain suggests (I think in his track work book but could be the chassis one) that on the real thing the track itself sinks in to the ballast as the train rolls over providing a degree of 'suspension'. This as I recall went alongside his theories of the flexure within the main frames from side to side.


Put yourself in the cess when a steam loco goes past. If the track is bullhead and chairs on wooden sleepers, it certainly goes up and down. I have not measured this but it looks like at least an inch for a big loco. I suspect more modern track is stiffer.

Having never put my head inside travelling mainframes I can't comment on that sideways flexure.



doesn't need to be steam, I have vivid memories watching diesels go by on bullhead and the rail moving up and down quite dramatically

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Re: Engineering, Injuneering and Knitting

Postby Julian Roberts » Tue Dec 19, 2017 6:45 am

The point is, real trains are very very very very very very heavy! How much would a 4mm axle load have to be to move the length of rail born by one single sleeper up and down like that?

Proving what Iain says. Models behave completely differently to the real thing so the problems are different and different engineering solutions are required.

I have seen that kind of movement in lots of places. I saw it worse about three years ago at a certain mainline location when I was on holiday nearby with time to spare, where every few minutes Class 185s 156s and heavy freight trains roared past at 80mph (or 60 in the latter case.) And been a passenger over the same spot, and being able to feel nothing unusual. Probably it's endemic and fairly harmless?

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Re: Engineering, Injuneering and Knitting

Postby Le Corbusier » Tue Dec 19, 2017 9:12 am

Julian Roberts wrote:The point is, real trains are very very very very very very heavy! How much would a 4mm axle load have to be to move the length of rail born by one single sleeper up and down like that?

Proving what Iain says. Models behave completely differently to the real thing so the problems are different and different engineering solutions are required.

I have seen that kind of movement in lots of places. I saw it worse about three years ago at a certain mainline location when I was on holiday nearby with time to spare, where every few minutes Class 185s 156s and heavy freight trains roared past at 80mph (or 60 in the latter case.) And been a passenger over the same spot, and being able to feel nothing unusual. Probably it's endemic and fairly harmless?


Wasn't Iain's espousal of a foam bed beneath the track, as opposed to cork, partially promulgated on the idea that this would allow the track to mimic life to some extent - rather than simply for quiet running? Perhaps this is where I subconsciously got the idea that the whole track bad acted as a damper .... without realising that models don't scale up and sometimes the full size bods will have to find an alternative engineering solution :D
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Re: Engineering, Injuneering and Knitting

Postby Tony Wilkins » Tue Dec 19, 2017 9:56 pm

Julian Roberts wrote: Didn't all locos have a specified minimum radius?

They certainly did and not just for horizontal curves either.
I do not have any figures available for steam locos, but typical examples from some diesel loco diagram books I have state the following.

Class 47
Horizontal without gauge widening 4 Chains
Horizontal with 3/4ins gauge widening 3.75 chains
Vertical convex 10 Chains
Vertical concave 10 Chains

Class 45
Horizontal without gauge widening 5 Chains
Horizontal with 3/4ins gauge widening 4.65 chains
Vertical convex 23 Chains
Vertical concave 24 Chains
Class 40 and 45s were banned from passing over humps in marshalling yards because of their lack of flexibility in the vertical plane.

Class 08
Horizontal without gauge widening 3 Chains
Horizontal with 3/4ins gauge widening 1.8 chains
Vertical convex 3 Chains
Vertical concave 5.5 Chains

It wasn't just Locos either. All rolling stock had official limits.
A Mk1 coach was limited to 3.5 Chains and this would have been at very slow speed.
A 16ton mineral wagon or 12ton box van could negotiate a curve down to 1 Chain radius but not I suspect whilst coupled to another vehicle.

Tony.

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Re: Engineering, Injuneering and Knitting

Postby Julian Roberts » Wed Dec 20, 2017 6:52 am

Most interesting Tony. Thank you. I note the difference GW makes to minimum radius of Class 08!

The answer to Tim's last question is on the next two pages of Iain's book quoted earlier. For simplistic souls please note that because I quote something doesn't imply my concurrence with every word. The camping mat tended to disintegrate with time apparently. See Allan Goodwillie's articles in recent Snoozes.

I am however proud to claim to be a pragmatist and seek a place at Iain and Mike's Kitchen Table.

20171125_224704.jpg

20171125_224721.jpg


20171125_224855.jpg


The resilience of track referred to by Iain is not I would think the type of fault in the earlier video. Rather, that of BH track by its design.

Tim sure you're right about granite, but any time I have read about track the ballast is referred to as being resilient. Concrete slab track is a very different animal probably.... :?:

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Re: Engineering, Injuneering and Knitting

Postby Le Corbusier » Wed Dec 20, 2017 8:40 am

Julian Roberts wrote:Most interesting Tony. Thank you. I note the difference GW makes to minimum radius of Class 08!

The answer to Tim's last question is on the next two pages of Iain's book quoted earlier. For simplistic souls please note that because I quote something doesn't imply my concurrence with every word. The camping mat tended to disintegrate with time apparently. See Allan Goodwillie's articles in recent Snoozes.

I am however proud to claim to be a pragmatist and seek a place at Iain and Mike's Kitchen Table.

20171125_224704.jpg
20171125_224721.jpg

20171125_224855.jpg

The resilience of track referred to by Iain is not I would think the type of fault in the earlier video. Rather, that of BH track by its design.

Tim sure you're right about granite, but any time I have read about track the ballast is referred to as being resilient. Concrete slab track is a very different animal probably.... :?:


Thanks Julian,

I had forgotten he touched on the resilient under layer in his chassis book. It was his track laying book which I was recalling .... where he goes into more detail. (Trackwork Prelininaries - 1:Trackbed and Underlay)
I have written at some length ..... as I am quite convinced that the right track bed can produce as great an improvement in the running qualities of model track as the use of modern finescale components produce in its appearance. Code 75 bullhead rail, though nowhere near as flexible relatively speaking as the real thing, will still flex sufficiently to perform a useful role in the production of a 'total sprung railway system' if it is laid on a suitable underlay, in such a way that its flexure is not adversely affected - which rules out the granite chipings and the PVA. The use of a ballast material that is, in itself resilient, will help to ensure that the track performs in the same way as the prototype, as well as keeping things sweet on the acoustic front.

His proposal was ....track built on stretched cartridge templates fully finished complete with ballast - then cut out. An isolated mdf track base on foam damper pads (though then mechanically fixed) with the tack composite then laid onto an additional layer of foam on this base, utilising double sided carpet tape - the edges of the cartridge is then bonded into the scenic section using PVA and a corrugated card strip.

discuss :)

Having just used granite chippings with a dilute PVA solution on a cork sub base I am somewhat hanging out there ;) My own initial thoughts were that for a pragmatic kitchen table approach it does seem extremely complex and the use of CSBs should vastly reduce the need for any of it. On the acoustic front perhaps simply isolating the track base (without rice's mechanical fixing) will suffice.
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Re: Engineering, Injuneering and Knitting

Postby billbedford » Wed Dec 20, 2017 11:13 am

It is obvious the the Crossrail engineers haven't read any of Iain Rice or Mike Sharman's excellent advice since 80% of the track in the new Elizabeth Line tunnels is mounted on solid cast concrete bases.

http://www.crossrail.co.uk/construction/railway-systems/
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Re: Engineering, Injuneering and Knitting

Postby Armchair Modeller » Wed Dec 20, 2017 11:37 am

...yet Brunel's baulk way was originally very rigid and had to be modified. Still, I guess suspension systems have improved slightly since the early days of the GWR ;)


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