Posted by Nigel Graham 2 on 12/07/2023 00:18:37:
…Now, how the heck is the exhaust pipe going to thread its way from the vicinity of the LP valve-chest not yet made, round the firebox while passing the injector someone has unhelpfully installed in its way, to the smoke-box connection only just higher than the axle?
…
Sent a "Help"! enquiry to the TurboCAD Users' Forum. I don't use TC much now and tried using Alibre again yesterday only after a very long break, but all of my inadequate, poor-quality drawings of my wagon parts are TurboCAD.
The one I wanted is a putative GA for the engine and transmission area. Or volume, rather.
I wanted to experiment with modifying the gears layout. TurboCAD's technique for moving drawing objects is very easy; but when I set the rectangle representing the chain-sprocket to go vertically, it moved horizontally! The X and Y directions had decided to change places but the planes-symbol still showed correctly.
Every object on this drawing raises work-plane error messages every time I select it, its co-ordinate values do not matching the Y-axis margin scale and non-existent X-scale. These are probably from TurboCAD trying to force 3D modelling mode.
That reversal of the two planes though, was totally new to me. When I re-opened the programme and drawing afresh, the same thing happened. Even more weirdly, it seemed to affect only that rectangle – oh, and its +/- directions are reversed too!
Hence my enquiry – what have I done wrong now?
The usual – trying to run before you can walk, changing horses in mid-stream, and leaving a gap long enough to forget Alibre! If you can possibly avoid it, don't take long breaks whilst learning CAD, and don't attempt two or more CAD packages at the same time!
Changing horses in mid-stream is a classic mistake. Both horses run away, everyone laughs when you fall in, even if you hit your head, drown, or die of pneumonia. Though I know FreeCAD, Fusion360, and SolidEdge moderately well, I find it difficult to switch between them. Their basics are all a bit different, so even simple stuff like creating a cube with a hole in it require a mental reset. Imagine owning two lathes where the controls are in different places and set up in the opposite sense: turning the carriage wheel clockwise moves the saddle right on one and left on the other; lever down to engage cross-feed vs lever-up; lever down to engage half-nut feed vs lever-up'; and then all these controls are positioned on their respective aprons in the opposite order. Even experienced operators take time to switch between contrary machines and are liable to get the controls wrong in an emergency. Alibre and TurboCAD have far more differences than a pair of topsy-turvy lathes.
I advise spending the time necessary to manually convert all the TurboCAD drawings into Alibre, and then dump TurboCAD. (Or the other way round if you must – the only daft choice is doing both!)
When 3D-CAD has been used to develop and assembly of parts, routing pipes between parts is relatively easy once how to draw lines in X, Y and Z has been mastered. But I would say pipe routing is advanced work, because it depends on mastering a raft of simpler tools and concepts first. Routing isn't beginner friendly.
I wonder if if would be better to develop the design using traditional methods rather than 3D-CAD?
Before plunging into Drawing Office detail, the original truck would have started as a series of rough sketches to pinned down the approximate location, size and weights of all the major components. Quite likely, several candidate designs would have been crudely small-scale modelled to check fit. Boiler represented by a cardboard tube, wooden discs for wheels, plasticine, wire and balsa etc.. This type of simple model makes it easy to spot major errors before tackling details, and it's likely several models of increasing accuracy would be made before the Drawing Office started work. And more models were often made to check and steer the Drawing Office as the design improved. Full-size prototypes were common: hopefully ready to go, but deliberately built expecting to find trouble before going into production. The process is slow and costly in time and materials, but not difficult.
Once 3D-CAD has been mastered, modelling on a computer saves an enormous amount of time and effort compared with developing physical models. But learning CAD is a major challenge, and the effort may not pay-off, especially if CAM isn't on the agenda as well.
So instead of struggling with 3D-CAD, why not tackle it traditionally. Make a simple model of the model to get the GA, and produce 2D drawings from that. The downside of course, is making models of models is time-consuming and not very rewarding – after a lot of work is put into painfully solving a problem, they're thrown away!
Here's a modern example, a Renault Twizy, made of clay, full-size by the look of it. Note the wheels, which aren't models!
Dave