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A First Attempt at 3D..
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* June 04, 2018, 03:12:25 PM
Assuming I've attached it correctly!

Don't get too excited...

It's not exactly a "rendering", just a drawing with the hidden lines hidden, of my preliminary design for the crankshaft for a miniature steam-wagon's engine. Finer details omitted, apart from the key-ways. The colouring was only so I could see what was what in the wire-frame view's tangle.

There are no drawings available, just contemporary advertising photographs and trade-magazine reviews with a few useful dimensions, for the prototype, a Hindley steam-wagon introduced 100 years ago this year and in production for only a few years. The engine, whose original cylinder sizes are given in the Edwardian trade-reviews for it, is unusual for such vehicles by being vertical, enclosed and mounted in the chassis between the crew seats.

The two pairs of large discs outside the cranks represent the eccentrics that drive the valve distributing the live steam in, and exhaust steam out, of the cylinders. They do so via a "link motion", set by a driver's control,  that makes one eccentric's motion relative to the piston travel dominate over the other such that the engine can be reversed, obviating using a reverse-gear in the transmission (a heady 2-speed arrangement).  Setting the pictorial ones to their nominal angles of advance round from the crank-pins, was tricky! I drew pairs of temporary radial lines on one end-view at the requisite angles from the crank centre-lines, centred the eccentrics as cylinders on the lines' intersections with a circle concentric to the shaft, deleted these lines and the circle, then chivvied the cylinders into their right places along the shaft.

Not quite first attempt at 3D either, because I'd been faffing around with assorted shapes for a long time, trying to make sense of a bewildering system. It's only recently that with a lot of Forum help I've began to grasp Snapping objects together at a simple level, and that in 2D only. The help was information the Manual does not contain, which is how to select the requisite drawing tools, the preliminary conditions necessary for them to work - and when they won't by design - or when they don't but ought, where to look for the problem!.

Unable to fathom out how to make 3D Snaps, Work-planes and Co-ordinate systems work, let alone co-operate, this is really just a line of similar, symmetrical shapes distributed by arithmetic along a common (0, Y, 0) axis on the default World work-plane. I found out, sort of, how to Subtract "boxes" from the cylinders that became the crank-webs, and similarly to draw the key-ways, but otherwise kept it simple, with all lengths (thicknesses) except the outer ends, set to a regular 0.60". That value both simplified the sums and produced something very close to intended size for assembly-fit and function, for what I'm trying to build.

 Since the engine doesn't need to be true to scale to something shown only in old photos anyway, as long as its external appearance is a fair representation, it also makes sense to design it around nice round decimals of inches to start with, to suit the machining, rather than model-engineering's more usual binary-fractions with all their secondary conversions to decimals. Superimposing circles to represent the cylinders I've already made showed happily, needing only minor dimension changes to match - but I could not find out how to do that here, which TC tells me is a mixture of "TC Surfaces" and cylinders.

I'd hoped to go on to add the connecting-rods, crossheads, pistons and cylinders, and the valves, at least, then the basics of its surroundings in the wagon, to help me work out how to fit the assembly into a rather cramped space - but will have to use a purely diagrammatic approach, and stick to orthographic projection for the parts drawings.


On TC Deluxe 19: hobby use.

* June 04, 2018, 03:27:33 PM
It looks like you've gotten the hang of this program, Nigel. I took the liberty of assigning a material and rendering your drawing...

Henry H


* June 05, 2018, 03:11:52 AM
Thank you Henry!

It does look better rendered. I'm a long way from getting the hang of TurboCAD though. I bought it primarily to be able to make isometric or similar views of parts and assemblies viewable in different planes, something I knew already is a fundamental feature of CAD, but have found it very hard to learn. I am not so worried about renderings as I'm after design & workshop drawings, rather than brochure-quality representations, but either way I'm far from being able to assemble collections of entities into cohesive wholes.

Where I wrote about "how to select a tool" I didn't mean how to open it from its symbol, but how to decide which tool to use to achieve what outcome; and very importantly, the pre-requisites for that tool to work. Many of the tools rely on your already knowing their concepts.

For example, I learnt with a lot of help that you can't hatch a cross-section unless within a polyline - a CAD concept new to me, not found in manual drawing. That polyline won't work if certain other subtle conditions fail, and these too, are not found on the draughting-machine. (I turn the auto-join option off, so though making more work for me, I can verify it's working or see any stop-points by the highlighting.)

And that's in 2D! 3D adds considerably to the complexity.

That crankshaft represents my present limit - like the assorted exercises I had concocted, it relies on very basic geometry of its own and its co-ordinate planes; and none of it was snapped together. Thinking about it, to add the primary parts of the rest of the engine to that drawing I don't need to try to design those parts in detail on it, since the drawings's purpose is largely to help me ensure the machine will fit where it should, and guide the detail draughting, which can be in 2D.  For example, I can represent the connecting-rods and the parts above them by simple 3D-primitve "cylinders" and "boxes", as long as they are in the right places and alignments. 

What I couldn't find is how to modify the sizes of some of the various entities so far, or stop odd effects like them drifting off-centre, but I can't spot any patterns in the causes and effects I'm getting. I don't know if object nature matters, as a Cylinder by Extrusion or Primitive, and TC Surface, all seem to me to have different Properties, judging by the menus. I suspect work-planes somewhere, but my attempts with those usually collapse into Escher-esque optical illusions! 

Incidentally I have had a little previous, very introductory, experience of rendering, via a pictorial programme called POV-RAY. This is not an engineering or architectural CAD application at all, and doesn't pretend to be, but exists purely to let you create pretty 3D-effect pictures by command-line data entries.


On TC Deluxe 19: hobby use.

July 14, 2018, 09:55:26 PM

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