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peter ravenscroft30/07/2010 19:27:11
88 forum posts
3 photos
oops thats what you get for reading it on the bus on the way home
you are corect it is 0.718 not 7/8ths as i presumed
regards
peter
KWIL30/07/2010 19:36:24
3232 forum posts
63 photos
Ian S C is "correct" if it is given in 1/32 then +/- 1/32 is OK,  as per his rule measurement, if in decimals, you takes your choice of how well you can work, 4th place on a DRO!
Dave Harris31/07/2010 08:43:39
28 forum posts
Thanks to all who have responded as above.
 
I have located and read the standards information in the Model Engineers Handbook and this agrees with all the construction books produced by LBSC and indeed the Loco Construction book by Martin Evans ie that the back to back dimension for wheels of 3 and 1/2'' gauge locos should be 3 and 9/32'', or 83mm.
 
Can the editor please explain the different 'back to back' dimension given on the drawing in 'ME'?
 
Also, i am concerned that it seems to be acceptable to 'mix' dimension standards on drawings? My mentors tell me that drawings should be drawn to one standard, and whilst in this day and age there is obvious 'discussion' over which 'standard' to use...imperial, decimal, or metric; that all drawings for a project should be to ONE standard.
 
Would the editor like to comment / explain why what would appear to be accepted standards seem to have been ignored for this construction series drawings?
Dusty31/07/2010 09:50:28
471 forum posts
8 photos
re Dave Harris's post
     Wheel standards do not apply to narrow gauge loco's. You must read the back to back dimension in conjunction with the flange dimension. Flange dimensions on narrow gauge loco's are far more substantial than main line loco's. If Martin Evans standard were to be applied to this loco the wheels would run on the flanges if run on a standard 3 1/2 gauge track. This would give an inside flange dimension of 3 19/32" patently 3/32" wider than the track. Hope this explains your query Dave. (yes I know I am not the Editor)
 
David Clark 131/07/2010 10:18:41
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3357 forum posts
112 photos
10 articles
Ray does say he has used different wheel standards in the article.
regards David
 
Dave Harris31/07/2010 22:11:52
28 forum posts
Thankyou for the responses. i regret to say I cannot understand the logic of using 'different standards' for NG locosas surely this is one area where the loco has to conform to track standards and not expect the track to conform to the loco? My other questions seem to have been ignored re drawing standards. i will retire from this forum, very confused and dissapointed!
John Stevenson31/07/2010 23:15:46
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Posted by Dave Harris on 31/07/2010 22:11:52:
 My other questions seem to have been ignored re drawing standards. i will retire from this forum, very confused and dissapointed!
 Sorry ??
 
Is it that the drawings are so messed up that you cannot understand them [ I have not seen them ] or is it that you expect every drawing to be of a standard even though they may have been prepared by  someone more used to making things than drawing things ?
 
If the first then I can understand your concern.
 
If the latter then, no don't bother - forget it.......
 
John S.
Dave Harris01/08/2010 08:30:30
28 forum posts
John,
 
   It a combination of both your observations.
 
   I do expect drawings produced for publication to be correct as far as dimensions are concerned, and to mix standards I feel is wrong as I said in one of my earlier posts.
 
   I am also puzzled by David Clarke's reply that 'different standards' are being used for this loco. I feel the standards in the Model Engineers Handbook are well known and should be adhered to for everybody's sake as tracks have been made to those standards for many years. Dusty's reply leaves me very confused, as, if the loco cannot be run on 'standard' 3 and 1/2 inch gauge track, then where can it be run?
 
   If the answer is to modify to suit current track standards then I feel that the series should have had this explained at the very start, especially for the benefit of 'beginners' like myself who, rightly or wrongly, expect the articles to be correct, and provide the means to complete a workable model,minor typos excepted.
JasonB01/08/2010 08:31:35
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18084 forum posts
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Well I thought that both Kwil and myself gave an answer as to why decimals may be used although it does not ap[ply in this case.
 
Its a bit much to expect the editor to spend his Saturday and Sunday reading through every post as I'm sure he does not get paid for it, perhaps wait until the beginning of the week to see if he replies. And also have a look back through some of the older posts as the same point has been raised several times in the past and I expect you will find your answer there.
 
Lets just be happy that people are willing to provide these drawings, Asd long as there are no errors I'm happy to work in any measurement or mixture
 
I would think that a narrow gauge loco by its very nature is somewhat top heavy and short wheelbased so thats why adjustments need to be made and they often also ran on tracks with a much smaller turning radius so a bit more "play" between the flange and the track is required if they are not to jam on the rails.
 
The Author also says its is "not unusual" for a narrow gauge loco to to use thicker flanges, so its not just a different standard being used on this loco
 
Jason

Edited By JasonB on 01/08/2010 08:35:05

Edited By JasonB on 01/08/2010 08:40:52

StirlingSingle01/08/2010 10:05:32
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40 forum posts
Hello,
 
Are the cylinders on this loco going to use Conway Castings and wheels?
 
Many thanks,
 
Stirling Single
steve milner01/08/2010 15:19:14
3 forum posts
8 photos
Hi sterling Single,
 
Cylinders are new castings to new patterns going to be available from Blackgates Engineering. Or you can machine from solid.
 
Wheels again available from Blackgates Engineering as existing 'Conway' castings but again can be manufactured from solid.
 
Hope this helps,
 
Steve
Dusty01/08/2010 20:16:26
471 forum posts
8 photos
Dave
       I am sorry if my reply confused you. What you must remember is that this Loco is scaled at roughly 1 3/4" to the foot. The wheel standards you are quoting apply to locomotives that are scaled at 3/4" to the foot. My current Loco is a 3 1/2 N.G. Loco. My wheel back to back dimension is 3 5/32", the flange is 1/8" wide, simple maths show that this gives a dimension of 3 13/32. A whole 3/32" narrower than the nominal 3 1/2" gauge track. I did not say as designed this loco would not run on 3 1/2" track, but there is a real danger that it would have a propensity to de-rail. I think that when I get round to building I will reduce the width of the flange to 1/8" this would in someway overcome the potential problem I have highlighted, without the need to completely redesign the axles. I dont know how Ray has got on with his loco, a lot depends on the accuracy of the gauging of his track.
Dave Harris01/08/2010 23:04:49
28 forum posts
Dusty,
 
   Thankyou for your clarrification.
 
   I have to say that I ran the discussion re this loco past some other model engineers and their reaction was that they would have used the 'standard' as per the model engineers handbook for the wheel profile, although one did say that if he were to do what your most recent post in fact has said, then he would have made it clear that some modification to the 'normal standards' would be necessary for the benefit of the less experienced. The 'fog' is gradually clearing!
Dusty02/08/2010 09:03:33
471 forum posts
8 photos
Dave
       I forgot to say that the wheels of my Loco are in fact 43/64 wide, even wider than Darjeeling Loco
KWIL02/08/2010 09:26:54
3232 forum posts
63 photos
Looking at our club standards, the flange width for 3 1/2" NG is 0.090", it is the tyre width that is much bigger on NG, 0.520 cf 0.370. The was a very comprehensive series of articles in EIM starting Jan 1994 which dealt with all the detail of guages, flange depths etc aimed at preventing conflicts arising.
Chris B02/08/2010 12:22:45
34 forum posts
5 photos
I would have thought with 3 1/2" the back to back would not be particularly critical for raised tracks as flangeways and check rails do not seem to feature on this type of track.
The problem area would be where ever 3 1/2" is "on the ground" and has points to negotioate.
In 7 1/4" there are std (6 13/16" back to back) and narrow (6 3/4") wheel standards but the track standard will accomodate both as the flangeway width and check gauge are big enough to accomodate the larger flange width. Although I found at my local club one particular point had been built particularly tight and I had to increase the back to back on the slate waggon I have just finished by 15 thou to stop it trapping the flanges and riding up.

Edited By Chris B on 02/08/2010 12:24:28

Dave Harris02/08/2010 20:28:18
28 forum posts
I am reading the responses with great interest and some confusion.
 
I am told by by other model engineers that even if one is building a 'NG' loco such as 'Conway' or the Dargeeling loco the back to back standard for 3 and 1/2inches still applies and that any machining of the wheel to a given size should not result in sacrificing the back to back dimension on the axle.
I note that the Conway wheels which are suggested for use in this instance are 1/4inch larger in thier tread diameter, and are 5/8'' thick, which would allow them to be machined back to the dimensions shown in the drawing for the 'Dargeeling' wheels  -  what I do not understand from all the previous posts is why the back to back measurement needs to be different to the already defined measurement given in the standards in the 'Model Engineers handbook' and as 'Dusty' has said, if left as per the drawing in ME, will give rise to a loco likely to derail. Surely if there are 'standards' for each gauge then whatever type of loco one is building to whatever gauge then the wheel treads and back to back measurements have to conform to the track standard?
I agree with Chris B that the main time this difference will show is on ground level tracks with multiple gauges and therefore using points. This may not seem to matter too much but it does mean that the standards set for our tracks, albeit a small minority of tracks, are being ignored for want of a better way of putting it and I still cannot understand why this has to be when it doesnt happen if building locos like 'Conway' or the smallest gauge version of 'Sweet Pea'?
Donald Mitchell02/08/2010 20:41:10
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90 forum posts
3 photos
Hi engineers,
 
I have been watching this thread about the wheel back to back size with growing interest.
 
Raymond McMahon is presently away from home on holiday; he will be returning on Tuesday 10th. Aug; and will no doubt clear up this dilema via this keyboard as soon as possible thereafter.
 
Raymond does not use the Internet himself.
 
Donald Mitchell
Castle Douglas
Bonnie Scotland
Dusty02/08/2010 21:38:49
471 forum posts
8 photos
I am afraid that a lot of you seem to be missing the point. In effect the back to back dimension means nothing, it is the thickness of the flange and the measurment over the flanges that is important. This measurement has to be less than 3 1/2" by, I would say 1/16". This is to allow the loco to run on the tread of the wheel as oposed to tight on the flanges. The larger the radius between the flange and the tread then the nominal 1/16" needs to be larger. In essence the thicker the flanges the smaller the back to back dimension needs to be.
 Playing the devils addvocate, if for instance we had a back to back dimension as per Martin Evans of 3 9/32" and flanges of 5/32" The loco would not sit on the track. I am afraid I cannot advance this any further. Everything in life is a comprimise especially Model Engineering.
Dave Harris02/08/2010 23:10:23
28 forum posts
Dusty,
 
I am sorry but I do not understand your logic.
 
If one takes a 'Speedy' wheel as an example, the overall thickness of the wheel is 9/16'', as for the Dargeeling wheel, the thickness of the flange is 3/32'' and the tread is 3/8'' and this allows for the 5'' gauge back to back measurement.I cannot see why with the same overall wheel thickness it is not possible to adhere to the 3 and 1/2'' standards already quoted.

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