Posted by Graham Williams 12 on 26/08/2022 10:23:25:
A little mystery: with the plan set I bought was two folders. All the parts had been hand drafted on A4 lined paper at a smaller scale – a tremendous amount of work! The chap I brought them from – Ben who is very much involved with full size steam engines – bought them from someone about 15 years ago – and didn’t know why this had been done.
As an old time draughtsman and more latterly design engineer (retired) I appreciate just how much work was involved in this.
I can only think this may have been the old version of what I am doing right now – modelling it in 3D CAD to “get the parts into your head”, or that it was just to have workshop sized drawings rather than having the A0 drawings laying around.
or is there another explanation?
Any thoughts or is this jogging someone’s memory?
Graham
Both good reasons Graham, but another strong possibility it was done to check the drawings for mistakes as these have been a problem in model plans from before Percival Marshall was a twinkle in his dad's eye! Various reasons:
- The draughtsmen's training was highly inconsistent; anything between tidied up back of an envelope to professional work, but possibly done in retirement to obsolete standards.
- Drawings were rarely thoroughly checked by others before publication. It's hard for amateurs and pros working from home to arrange proper review, and there's no formal authorisation process. It's extremely difficult to spot your own mistakes – we see what we expect to see!
- Once issued there is no version control. Over the years many drawings have been copied and amended by different people at different times. They corrected some old mistakes, missed others, and added new ones! It's a muddle.
- There's no standard way for mistakes to be catalogued or corrected. Be nice if mistakes made by LBSC up to a century ago had all been nailed down, but no – they're catching people out.
In short, a serious uncorrected quality management problem caused by not following the full engineering process. Hardly surprising as Model Engineers are disparate hobbyists, not a disciplined team of well trained and consistent experts! Fixing all the bad plans at this late stage would need someone determine and energetic to organise a CAD group to clean up by recreating the designs in 3D, operating strict peer review, and then version control.
So if I have any doubt about a plan, I redraw it to make sure I understand it and to flush out errors. Very often, a few dimensions will be missing or wrong, and sometimes more serious mistakes creep in, like interferences.
Dave