David Hoskins

During many years of building locos, mainly from kits, I have never been able to see the sense of sprung axles, unless you want a prototypical look-alike chassis and a lot of extra build and commissioning effort.

The following are my suggestions for the minimum requirement for good running using regular bearing bushes, and the axle centres in the frames of an etched kit.

1 The driving (motorised) axle should be fixed horizontally and laterally but be allowed plus or minus 1mm of vertical play. The motor and gearbox should be restrained, but allowed to rotate up to five degrees by clamping the motor body to a sprung angle bracket with a cable tie. The net result of this effort is a rocking axle irrespective of its position in the chassis. In other words, it can drive on the middle or rear axle.

2. The forward axle, irrespective of the number of axles, should be fixed laterally, horizontally and vertically. This is very important when using external valve gear.

3 Assemble these two axles without motion, valve-gear or pick-ups. Place the assembly on a sheet of glass or a flat section of track and check that it sits square and doesn't rock. Place a strip of 0.5 mm brass or plastic under one wheel and check that all four wheels remain touching the glass or track. Repeat this procedure for each wheel. The driving wheel axle hole upper and lower extension (ovality) should be increased to get this right.

4 All the other axles can use fixed bearing bushes. The lateral play on these must be increased depending upon their position relative to the driven and front axles and the end user's operational track radius. If you're concerned that the driving wheel bushes will rotate in the oval chassis holes then modify this position as shown in figure the above drawing.

Another useful device in loco building is a metre of track fixed at a 6ft radius onto a portable plank of wood. A more expensive solution is use of 72 inch LH and RH turnouts fixed end-on-end. Use these test benches at each stage of the build especially when fitting the valve-gear and motion. P.S. The floating axle shown in the photo can also be used on the middle axles of tenders.