Multi-dimensioned Drawings

I'm sure publishing to a hobby audience had far more to do with it than engineering best practice!

Model Engineering Plans are often eccentric by professional standards, for all sorts of reasons. They range between excellent and downright misleading. Using the same drawing to redimension similar parts is asking for trouble in manufacturing, but not a bad idea for economy minded hobbyists wanting to build the same engine in different scales. It does require the hobbyist to be wide-awake though!

I never trust hobby plans entirely, and always do sanity checks before making anything. Safer to assume model engineering plans are flawed than to blindly trust them! The check might be a basic sketch, or a full 2d CAD redraw to confirm many dimensions, or modelling whole parts and assemblies in 3D CAD. 3D Modelling is useful because it often suggests how parts might be machined for real, as well as confirming their shape and dimensions. (In a sense 3D CAD modelling really makes parts, rather than representing them 2D on paper, which is error prone.)

In my limited experience sanity checking reveals fairly quickly how good or bad the plan is. Although cluttered the PottyMill plan I found on the internet proved sound, as was Stewart Hart's properly laid out original I came across much later. Same can't be said of some of the plans in old ME's, where the number of question marks often suggest a full review is necessary! Mistakes are fairly common, more difficult are missing dimensions and reference points, and parts that can't possibly fit together. LBSC plans are inconsistent, ranging from crystal clear - the famous words and music - to unsatisfactory outlines, probably never built, and perhaps only published as suggestions rather than practical designs. To be fair to amateur plans, draughtsmanship isn't an easy profession, and drawing offices usually cross-checked and reviewed everything with a team, corrected mistakes promptly, and applied proper version control. More work than most of us have time for.

No matter: I'm a gentleman dilettante who likes making things, indulging interests, who has no need to earn a living from my tools. Iffy plans are deeply frustrating if get-on-with-it perfection is expected of them, but all part of the puzzle solving fun once you understand they are often flawed. And they often are...

Dave