Thank you Steve.
There's always something that doesn't quite go right first time with these things, but it's good to know you've identified the weakness and solution.
My own long-delayed project is a one-third-size Hindley steam wagon whose full-size prototype was launched in 1908 , and the big hold-up at the moment is the engine, an enclosed, vertical compound unit very unusual if not unique, for this class of work. The engine's place in life is equally unconventional for its day, between the two crew seats, and just in front of the cargo platform. I've no drawings, just some copies of 100 year old photos and few dimensions.
I've now found a candidate engine design, actually for a 5"-gauge locomotive, but the geometry and valve ports are close enough for adapting to the wagon. I'm now using TurboCAD for a General Arrangement of that adaptation. My attempt at an image of the crankshaft that I posted on here some while ago, was a preliminary drawing for this engine's shaft. I submitted it in wire-frame format, but someone else, Henry Hubbich I think, kindly coloured it in for me!
The GA, and any subsequent drawings using TurboCAD can only be all orthographic, because unfortunately I have failed in trying to learn 3D enough even for single, simple parts of the machine, as I'd have liked; let alone complete assemblies. However, it should still perform two important functions: assessing fitting the unit in the limited space available, and of helping me overcome two problems I unwittingly created when I made the chassis too many years ago.
1 The vehicle has Ackermann steering, so the chassis rails have to be swan-necked inwards, but I didn't realise at the time that one of them would cramp the space available for the transmission, and in an awkward manner! Nor that they should have come in a bit further still to give a tighter turning-circle.
2 The way I modified a car front-wheel-drive differential to carry the final-drive chain sprocket on a proper traction-engine type live axle, places the chain a bit too far inboard, cramping things even more! Much later I acquired a further, original manufacturer's photo showing the layout I should have followed... had I known.
So at least I can use TurboCAD to experiment with designing the 2-speed gear-set and its place relative to engine, drive-chain and chassis, before physically cutting metal.