Guy Rixon wrote:Things likely to fall off, from observation:
* Six-wheeled coaches, on plain line. Happens each time anybody farts in the same postcode, on both P4 and EM. .
Such a memorable thought has stayed in my mind challenging me to see if it's true. This nice BZ kit was on sale at Scalefour North in April and is just the job as something appropriate for 1950s/60s exCR/LMS BR Calderside. The plan was to make it on wet days during caravan holidays where a steam locomotive is too complex. But there haven't been many so it's still only half built.
The kit design which is for 00/EM envisages the centre wheel assembly sliding sideways as it enters the curve and, being linked to the outer wheels, steering them to thereby stay more or less at right angles to the track. As I don't intend anything less than say 4ft radius I thought there is no need for the outer wheels to steer. Indeed I have a SR 4 wheel van of the same wheelbase that goes fine. So the centre wheel assembly is fixed and the wheel given enough sideplay to be able to slide laterally within its bearings, which is no problem with the design being for the narrower gauges.
The design sees a piece of NS wire folded to provide a downward spring force on these centre wheels, with one of the outer wheels being able to rock.
I made up the basic chassis and basic bodyshell to test out Guy's assertion here. I found that the downward spring force was not sufficient for the centre wheels to be made to slide laterally. They preferred to mount the rails. So I replaced the wire with steel wire as used for AJs. Much 'tuning' or fiddling was required to subtly modify the shape of the curving fold to exact an appropriate spring force. What is required is to balance the force against weight added at each end. Too much force and the outer wheels are not firmly enough on the track. The more the weight the more the force can be. The weight must be as far as possible towards each end. I managed to find what I think is a medium balance where the vehicle weighs 90g while the centre wheels feel satisfactorily positively sprung. Perhaps a bit heavy but fine for me.
Lubrication of the centre axle is of course vital. Below is a picture of the centre wheel assembly and one of a test stage. The kit is very nice to make and the designer very kind and helpful with subsequent questions I had.