while we're on the subject... I'd value some input on steel for the following:
one of the things I'm doing requires a stub axle to carry a wheel. This is
20mm dia., and I currently make them (as described in more detail recently) from 20mm bright MS, drilled for lightness.Now, 20mm bright, as I drill it (8mm hole at the maximum stress point, working out to 16mm at the extreme ends) is plenty strong enough. It's got to take half the weight of an adult trike plus rider (assuming the other wheel is lifted in a corner) and currently the same axle is used on tandems (hence twice the load) - not heard of any problems, so I assume the solo one is rather over-spec.
The axle has to be 20mm so it fits 20mm ballraces in the hubs, BTW.
The axle is currently 124mm long, it fits in a mount and a hub with a combined length of just over 124mm, and is all held together with a Q/R 5mm skewer down the middle (basically, a long 5mm bolt with an overcentre clamp on one end, if you've never seen one). The main thing this does, apart from stopping the wheel from falling off, is to pull all the spacers etc. between the ballraces and so on together solidly. I could equally well us a long, thin bolt, but then it's not possible to remove the wheel without tools, which it is now.
The main load is obviously a bending moment, at the point between the mount and the wheel inner side bearing. This has an alloy spacer about 14mm long, and it's in this area that the centre hole is 8mm.
OK, that's the job described. The current axle was tested by the unscientific but basically effective technique of holding it tight in the vice, putting about 8ft of tube over the end, and trying to bend it. It didn't; not at the sort of load that left the vice still attached to the bench, anyway.
in the early prototype stages, we made one using standard bike axles, which are 9mm solid but not plain mild steel, and these bent. Sturmey Archer supply hubs for singe-sided mounting with what appears to be a fairly ordinary 12mm bolt, and one would hope that they've tested this. I don't think they recommend those for tandems, though. So, your thoughts, please, if you've not got bored and wandered off. Can I get better steel which I can still machine? I don't really want to get into heat treatment, haven't got the gear for it.
If I stick with Bright MS, am I being over-cautious with the drilling?