5" gauge axle diamensions

[ivanp]

hi all
I have a question, I am building a 5" gauge loco and i have noticed that some designs call for axle length dimensions as 4 5/8 back to back while others ie simplex 4 11/16
also the wheel thickness is 5/8 or 11/16 respectively
any body know why or does it matter?

Ivan

[Boadicea]

I don't know the answer directly to your question, but our very own Alan Stepney tells us what it should be here (and much, much more!)....

www.alanstepney.info/page24.html

Regards, Bo

[Lurkio]

Hi Ivan,

There'll be better qualified than me on this forum to put you straight on this one, but I'll share my own thoughts for what they're worth.
I found a similar problem searching out the 'standards' for 3 1/2" gauge - different sources gave different dimensions.

Seems the standards have evolved over the years as the overall scale quality of locos built has improved. LBSC's old drawings appear to provide amongst other things for a wider (read coarser?) wheel than is recommended today. Make them narrower though and any outside motion etc. has to be made to suit of course.
Back to back though I always found the same dimension recommended - surprised you've come across a difference there, as this definitely needs to be correct.

As I understand it, in the early days models were mainly used up and down a straight, so axle lengths were not too critical. Nowadays with curves, points, crossings, check rails etc., back to back wheel dimensions are important to prevent derailment.

I finally decided to stick with LBSC's drawings for overall dimensions, but to use the wheel profile as shown by Tubal Cain in his Model Engineer's Handbook (usual disclaimer) - all the modern standards are there, and without actually checking, I think they tie up with those on Alan's website as indicated above by bo.

Lurkio.

[jgb7573]

Hi Ivan,

The most critical dimension for wheelsets is the back-to-back dimension, particularly if you plan on running on tracks with points. This dimension makes sure that when the wheel is approaching the frog, that the check rail by the 'outer' rail pulls the wheelset over so that the 'inner' wheel goes on the correct side of the frog.

There are two different standards for 5" gauge for historical reasons I believe. I know that when the points were designed on the IDSME track this gave rise to some head-scratching, and we ended up with a design that coped with both standards by wangling tolerances. It gets more involved still with mixed gauge points as the 'outer' check rail works for both the the 5" and the 3.5" frogs. I dare say the same compromises apply for mixed gauge 7.25" points. I think you'll find most club tracks with pointwork will support both 5" gauge standards, so choose one of them and stick with it!

[Shawki Shlemon]

Hi Ivan
Here in OZ this has been a point of discussion for long time . In brief the 4 11/16" is fine scale size and I use it on most of my engines .
Also we have here a narrow gauge size and it is 4 9/16" and is widely used in Australia . Someone will correct me if I am wrong the 4 11/16 will run happily on a track designed for 4 9/16" but if the track is designed only for 4 11/16 ,the 4 9/16 could experience problems through the points . If the track is designed for narrow gauge and fine scale then all engine (back to back 4 9/16 - 4 11/16 ) will be OK assuming the 5" dimension and all other dimensions are wright .

[GeorgeRay]

If you are using or intending to use David Hudsons self steering wheel sets and bogies he says stick with 4 5/8", increasing the back to back to 4 11/16" adversly affects the behaviour of the wheel sets. This of course assumes that the SMEE wheel standard is used for the flange dimensions and the wheel is 5/8" thick. Our club is just about to start building passenger trolleys using the self steering design so we will be sticking with the smaller dimension.

[alanstepney]

There are, confusingly, several "standards". Or to be accurate, several people/bodies have suggested standards over the years.

LBSC used one, which was, from memory, the same as proposed by Henry Greenly.
Martin Evans used a slightly finer "standard".

The first real common one was that proposed by the SMEE, which many clubs adopted for their tracks.
Derby club made some minor alterations to that in their superb articles about multi-gauge tracks.

Tubal Cain published the then latest proposed standard, and, yes, it is the same as on my website. Around that time, Model Engineer also published it, and SMEE and other bodies tended to stick to the same major dimensions with only very minor differences.

Then along came the narrow gauge enthusiasts.
That meant some changes to keep to something that was scale, but would still run on standard gauge tracks, particlularly multi-gauge club tracks.
Again, a compromise was the answer.

Of course, go across the "pond" and everything changes, but I wont go down that route in this thread!.

At present, I always build to the standards on my website, and if that means changing other dimesnions on the loco to suit, then so be it.
Of course, for anyone planning to run on a specific club track, such as Derby, where they have a recomended standard. it is worth sticking to what they suggest.

[ivanp]

Thank you to all that have replied
I am going to use the 4 and 11/16 dimension
as this is what the latest drawing states , the original drawings and subsequent construction articles that appeared in EIM stated 4 5/8"
hence the original question.

Thanks again for your input
best regards
Ivan