don9f
Statesman
Les Warnett 9F, Martin Evans “Jinty”, a part built “Austin 7” and now a part built Springbok B1.
Posts: 961 
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Post by don9f on May 24, 2020 18:49:02 GMT
Agree completely with Julian’s comment and I think it was concluded some time ago that Ron’s B17 did in fact have the “all square” arrangement and the 90 degree value is valid on that design.
Cheers Don
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Post by silverfox on May 24, 2020 20:31:03 GMT
Reg
Thanks for the spreadsheet.
However as i dont hasve knowledge of e,k and a, and cannot figure out whau is! unless it is the arc length of the expansion link ( halved)
It looks as though i am onto a non starter and will have to resort to the expanding/retracting eccentric rod
Thought for a second i had found the golden ticket!!
I think both M Evans springbok and D Youngs A3 do have the same diameter diamenter. one , cannot remember which, is at 90" degrees, he other slightly out which didn't really help me!! Hence the original question all that time back
If anyone wants to have a stab at the possible radius of the B17 return crank i can send across all the known dimensions, Meanwhile the guessrod!! construction now commences
Thsnbks
Ron
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Post by d304 on May 25, 2020 7:29:02 GMT
Julian, you are correct. Looking at the article in ME “Some practical hints, 15 June 90” there is no mention of the inclination.
Ron, lay the information on a piece of paper as I have( starting learn Autocad 360 through son) and with arithmetic and subtraction the answers are there!
David
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Post by d304 on May 25, 2020 7:36:37 GMT
The Wallace simulator does produce a PCD!
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Post by RGR 60130 on May 25, 2020 8:26:23 GMT
For those who haven't input data into a simulator before, they usually require you to enter data that uses the centre line through the cylinder and driving wheel as the horizontal reference. The attached drawing shows some examples. Reg  VG Dimensions by George Rossiter, on Flickr |
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jma1009
Elder Statesman
Posts: 5,926
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Post by jma1009 on May 26, 2020 21:06:17 GMT
Hi Reg,
One issue I have with your above pic is that the angularity of the connecting rods is not made clear, if it is there at all.
I have waited a day or so hoping someone else might point this out before me!
When such a pic is presented, I take the view that the motion centre line should be showed if it has an inclination ie not horizontal. I take the view your's does have an inclination, but this is not clearly shown!
Cheers,
Julian
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Post by Oily Rag on May 27, 2020 20:25:38 GMT
I agree that some published designs are deficient in various respects, but I think we should avoid being too harsh on the designers. Don Ashton was an absolute master of valve gears, but in the absence of his published findings, how many people understood the finer points at all? LBSC, Martin Evans, Don Young and co. had to be reasonably familiar with all aspects of design - not just valve gears - and also know how to put it across as journalists (probably against the clock - that's how magazines work). I think they did their best within the limitations they had to work with. Full size was not always that brilliant either I am re-reading Eric Langridge's memoirs ("Under 10 CMEs") and although he had a valve gear model to play with, a degree of "rule of thumb" was also involved. He says that the inside valve gear for the Schools class as taken direct from the Drummond D15 design, and he comments elsewhere that "Walschaerts valve gear more or less designs itself". Then there is the case of the Joy valve gear on the LNWR 0-8-0s - noted for highly uneven valve events. Late in the day, someone managed to shift the position of the Joy slideshaft and got perfectly even beats - but "management" decided it was a major operation and it was more cost effective to let them plod on going "dot and carry one" for the rest of their lives. My suspicion is that, if Don Ashton had published his work half a century earlier, a lot of full sized locos would have had better valve gears. The model designers, for the most part, were amateurs like us, sharing the knowledge they had - and where would the hobby be without them? Malcolm There are a lot more published model engineering steam locomotive designs than what Don Young, Martin Evans and numerous other UK based designers put out into the world. They are just the UK based ones, consider the USA, New Zealand, Australia, Germany, Japan and .............................. a lot of locos and a lot of grief. I will concede to aspects of the relationship with the hobby and time constraints, however I feel that often not enough effort is out into the design, building it and then proving it before publishing. I am very familiar with the situation that for example Martin Evans was involved with. |
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Post by Oily Rag on May 27, 2020 20:41:17 GMT
Hi Reg, One issue I have with your above pic is that the angularity of the connecting rods is not made clear, if it is there at all. I have waited a day or so hoping someone else might point this out before me! When such a pic is presented, I take the view that the motion centre line should be showed if it has an inclination ie not horizontal. I take the view your's does have an inclination, but this is not clearly shown! Cheers, Julian For the purpose of input into for example the Dockstader simulator the Cylinder, crank axle centre line angle to horizontal is not required. For all intent and purposes the inputs work as if all is horizontal. For example the QR C17 has a 1 in 19 inclination, about 3.05 degree if I recall. So one thinks as if the drawing is rotated 3.05 degrees clockwise. This does require a wee bit of care if the drawings show some dimensions perpendicular to the cylinder centre line and some crucial dimensions in X and Y from a horizontal line and or vertical line, as the Queensland Railways drawings often do. CAD or paper drafting will assist to resolve this. One problem that may exist is if the cylinder centre line does not line up to the driving wheel axle, this is not unknown. Also if the valve rod centre line is not parallel to the cylinder centre line, again not common but does occur on the odd occasion. The Dockstader simulator I think does not accommodate such instances, I have no idea of other simulators. |
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Post by silverfox on May 27, 2020 21:21:38 GMT
d304
Where can i find this wallace simulator?
The only link i get is for an anxiety, and depression test, which i would certainly qualify for in working out my PCD!!!
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Post by Deleted on May 28, 2020 9:23:44 GMT
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Post by d304 on May 28, 2020 10:39:14 GMT
Maybe we need the “Wallace Stimulator” to find the elusive PCD!
Yes as Greendlade said, Ashtons site under downloads. Fill the required boxes on the first page of the Excel spreadsheet and if you look at the tabs at the bottom, the information like PCD are generated.
David
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jma1009
Elder Statesman
Posts: 5,926
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Post by jma1009 on May 28, 2020 20:45:23 GMT
Hello David,
Don provides the mathemetical proof/equations for this in his book, but then adds the proviso on p.7 that unless you can make everything exactly to 'toolroom standards' then he sets out the procedure that stevep and I have set out on here.
The PCD of the return crank is not that important anyway - after all it ends up connected to the expansion link that then alters this throw and is adjustable. Don was quite keen on the expansion link not having too much swing, that can make reversing difficult when the loco is stationary.
Cheers,
Julian
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Post by d304 on May 29, 2020 0:48:38 GMT
Hi Julian
My thought is that if the parts are made to “tool room standards”, then the dimension of the eccentric rod would would have a known dimension, not something approximated on assembly.
My current build, the valve gear was finished using the dividers and adjustable eccentric method and runs well on air.
David
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Post by Roger on May 29, 2020 10:05:46 GMT
Hi Julian My thought is that if the parts are made to “tool room standards”, then the dimension of the eccentric rod would would have a known dimension, not something approximated on assembly. My current build, the valve gear was finished using the dividers and adjustable eccentric method and runs well on air. David Hi David, This is true, and Don Ashton's drawing for SPEEDY's new valve gear defined everything. If the valve gear dimensions have come from a simulator, then all of the dimensions must have been defined. I made everthing to the drawing, and it seems ok. |
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timb
Statesman
Posts: 512
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Post by timb on Jun 4, 2020 9:56:46 GMT
Thanks Reg for a great explanation, my understanding of what is going on with this gearing arrangement is much clearer now. From some of the other comments it would appear that getting this right is almost impossible to do without detailled knowledge and absolutely accurate machining, yet there are many working examples out there for all to see! It gives hope to us lesser beings!
Tim
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