Thank you Jason.
Also, thankyou David for sending what the rail should look like.
Ironically I realised only this morning when thinking about what I need re-measure, that for practical purposes I need only that trapezoidal centre section.
It will hold the engine and transmission, which have to be connected around the final-drive chain sprocket whose location became fixed by the axle and radius-rods I made too many years ago.
If I ignore everything outside that tapered area, I might be able to draw just that part of the frame correctly. They consist of the two side pieces and one cross-member, all channels; and a second cross-piece, of angle-section. Still problematical though, because the outline is a trapezium, not a rectangle.
If modelling the entire chassis I could represent the channel members as solid bars – but why even try to model the full chassis?
There is no point trying to model the whole vehicle in 3D CAD, even heavily simplified. If I tried it, it would be very incomplete as I’d have to simplify much of it and omit everything too hard to draw, including the steering links, springs, brake rigging, boiler fittings and pipework. This beast is proving easier to build than to draw, despite continually having to revise existing parts and overcome built-in errors!
I don’t know why I thought I would eventually be able to model it in 3D CAD. I think someone here suggested it. Aye – them as finds very hard things easy, tend to think those easy for everyone.
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I need draw the machinery properly, but almost everything forward and aft of that machinery space is nearly complete, made mostly without drawings, though needing a lot of finishing and some revising.
There are “only” two major items to make other than the engine and road-gearing:
– The proper steering gear-box to replace the present, temporary arrangement. That needs proper drawings. I might be able to model its components in Alibre, with suitable simplifying; but not the assembled mechanism.
– The boiler cladding sheets. They cannot be drawn using CAD, only marked out from cardboard templates measured and cut to fit (The other “CAD” !)