This is not something you should ask model engineers, as many of them will say that of course it should be fully sprung, as per prototype. But you are not making a model – you are making a small locomotive to do a job, and have some fun with.

You can certainly get away without springing on a simple loco that is only going to run slowly, but a bit of "compliance," and not necessarily conventional springs, will improve running as you say, and give better adhesion, and it need not be a lot of extra work.

Look at the earlier Maxitrak 4 wheel locos for ideas. Some have two rigid axles and some have only one axle sprung, or pivoted centrally to provide compensation. These are successful commercial products that pull loads and stay on the track.

It is in the axle box sliding bit.

It is a good idea to provide at least one axle with suspension. Model tracks are seldom level and points and joints often have discontinuities.

On a freelance model it is also a good idea to put in guard irons and horizontal stretchers just above the rail level so that when the loco or driving trolley do come off they land on that not crashing down on the sleepers and possibly bending brake gear etc.

Pm sent.

Just in case it's not obvious the important thing about back-to-back is for the wheels to pass though the check rails on points but at the same time not be wide enough for the wheel flange to hit the nose of the point frog. However the wheels need a bit of clearance to avoid jamming between two opposing check rails. I suspect your supplier was thinking of this.

SMEE standard for back to back is 4.687 (119 mm), just looked it up, so is GL5

Edited By duncan webster on 10/05/2018 14:44:15

Springing will improve its adhesion, and therefore its pulling power.

No springing won't stop it working, but it will work better wit at least one sprung axle.

If you want simplicity, copy what I did for my driving truck. Each axle passes through a swinging arm at each end, with a ball race fitted in it. The ordinary ball race happily permits a small amount of mis-alignment over the width of the axle. Springing is just a piece of dense rubber between the arm and the chassis which has the advantage of being progressive and largely indifferent to the exact size and position of the block. It works perfectly, unlike teh original springs with adjusters the blocks replaced (see below).