Landships II

Basically the dishing strengthens the wheels and makes sure they take transverse loads (or partly transverse ones, with components along the line of the axle) in a predictable way.

George Sturt's lovely book is quoted here - http://www.wheelwrights.org/craft/history-of-the-wheelwrights-craft - and is well worth looking at if you like wood or carts.

and

http://wantage-museum.com/wp-content/uploads/2011/03/Wheelwrights.pdf

THis has stuff on wheels and dishing too but I have only just found it and have to go before I can explore properly ... http://www.lostcrafts.com/Carriage-Building/Practical-Carriage-Building-Main.html

I'm not quite sure what you mean about the difference between 'conical' and 'dished' - surely all such wheels are basically conical? Perhaps it is an artefact of the spoke shape? Or just bad workmanship/I would be surprised to see spokes that were actually curved, as 'dished' in your sense implies, as they would be bending and therefore undergo worse bending under load and lose compressive strength = risk of runaway buckling failure, rather than taking the load straight along the axis of a straight spoke. Pre-stressing doesn't make sense to me as the hub would just get pushed out even more.

Not sure about why 12/14 spokes, and someone else has my copy of Sturt, but obviously the more spokes the more joints and the more holes cut into the felloes (bits of the rim) and the less room for the joints between the felloes and on the hub. And more spokes too. Costs more.

My very strong instinctive reaction is that 12 is blindingly obviously (OK, well perhaps not obviously!) a better number because it is easy to mark out 12 spokes by geometry. I do no tknow how they did it in fact. But 12 = 3 x 4 and straight off the top of my head I can see how to do it with nothing but a pair of large compasses and a ruler. Draw a triangle, use the compasses to find the centre, then draw a circle on that centre, mark out the lines from the centre through the angles of the triangle to get the first 120 degree arcs, and then twice bisect each arc with the compasses to get the 12 rim/spoke joints. If the felloes are to be identical, too, which surely they have to be for even loading, then that means a minimum of 7 felloes (x 2 holes each). That's one more felloe, 2 more spokes and 5 more joints for 14 rather than 12 spokes.

14 is 2 x 7 and such a pain to mark up that one would have to make up a jig, effectively, so you only have to do it once and then can mark succeeding wheels. This is much more reasonable for artillery of which a lot of identical-ish wheels were produced. And who cares about the cost if the MoD, or its predecessor, is paying?

I stand to be corrected of course!! - and will be very interested. It's something I've been wondering about myself, having been very disenchanted with a couple of kits of Great War artillery which forgot to dish the wheels (amongst many other flaws and omissions).

-- Edited by Lothianman on Thursday 7th of February 2013 11:56:06 PM

-- Edited by Lothianman on Friday 8th of February 2013 12:04:48 AM