In response to BOB2's post above, that's correct, springing won't greatly affect pulling power and tracking. It DOES improve reliability in terms of staying on the tracks by maintaining some downward force on the axles at all times, so the loco can't lift a flange over a rail if it encounters a bump in the track. I am just getting started on rebuilding an AHM-Rivarossi 0-8-0 with springs, my first O-scale loco, but I have built stuff with springs in other scales.
The method I found works best is to design the axle boxes to rest against solid stops, (e.g. top of axle slot, or perhaps an adjustment screw? I never thought of that until just now!) and set up the springs so they only come into play if the loco encounters a bump. Setting up a loco that is 'floating' on its springs is a complete pain, much trial-and-error to get to sit level & at the right height. To work properly the springs have to have a fair bit of travel but this freedom of movement can cause problems. Sometimes a loco can even lean sideways on curves. Also, I have seen a loco that was worse for derailing after having springs fitted - turned out it was 'rearing up' when pulling heavy trains and lifting its front drivers off the rails, because the drawbar was tending to pull the bum of the loco down and the floating-spring arrangement allowed it to do just that. If a loco has stops for the axle boxes then you know it's going to sit level at the right height, and finding a suitable spring gets easier because its strength is not so critical, they can be quite weak and still do their job. The depth of the holes is not so important either - that's really helpful, 'cos unless you have a milling machine it's not easy to drill the holes exactly the same depth.
The 0-8-0 is being a bit of a nuisance; axle-box slots are different depths, so right now I'm figuring out what size packers I need to make them all the same. Regards, Paul - Whangarei, NZ
