So on my first day at work as a trainee draughtsman I’m shown my drawing board and seat. Behind the seat is a desk where upon lays some drawing implements.
There’s a T-square, protractor, a few technical pencils, a rubber, erasing shield, ruler, compass, some circle stencils, a scratching pad which is basically sheets of fine sandpaper, a scalpel and a large orange brush that is apparently made from horse hair. I think that’s because it generates less static electricity.
It was always entertaining to swipe all the little pieces of rubber over to your co-workers drawing board, especially when they are really concentrating hard and have their nose a few inches from the board… so I’ve heard.
The yellow pen had 0.9mm lead, the blue pen had 0.7mm lead and the black pen had 0.5mm lead. The difference size leads would represent different parts of the drawing. That way it would be clearer to read for any manufacturer or fitter.
Generally the 0.9mm pen would be used for text, 0.7mm pen would be used for the outline of the component and 0.5mm would be used for hidden detail, dimensions, hatching and centrelines.
The Drawing Office manager would produce drawings that looked like pieces of art work and I found it unbelievably difficult in the early days to make mine look barely respectable. There is a real skill to being a good draughtsman and it takes many years to hone that craft.
I spent around 3 years using a drawing board before CAD came in and I’m proud to say I reached a high standard. One of the most difficult elements of draughting is writing neatly in block capitals and this was something I struggled with for a long time and if anything that was still a bit of a weakness even at the end of the drawing board era.
One of the tricks to drawing neat lines is using the scratching pad. If you were to snap the lead in a technical pencil and then draw a straight line of say 200mm the line thickness will differ along the length and it will most likely look lighter and darker in places. What I did before drawing every line was to gently rub the lead to a 45° angle on the scratching pad. Then try and apply a constant pressure whilst drawing the line. This way you would get the correct thickness and a clean crisp looking line.
I studied CAD for a year at college on day release before the company I worked for purchased their first CAD software. This leap from the drawing board to CAD couldn’t come soon enough for me as by then I knew how superior CAD drawings were to any that are hand drawn.
I think the first few CAD drawings I created were simple labels and brackets. The mistake I made though was to plot them using only a 0.7mm pen in the plotter. The CAD drawings to be honest looked a bit rubbish and the boss wasn’t overly impressed.
Without setting up line thickness correctly engineering drawings really do look awful. I quickly ordered some 0.5mm and 0.35mm pens for the plotter and setup some simple layers in AutoCAD that would represent the line thickness. The difference that made was striking. All of a sudden I was producing drawings that looked far neater than any of the hand drawn stuff before and thankfully everybody seemed impressed.
After a few months or so the drawings were getting much more complex as I was exploring the limits of CAD. I remember one day an old contractor who designed automotive dispensing heads for us popped in and rolled out his latest design for review. The drawing was hand drawn and on an A0 size sheet. It had some very complex section views, and credit to him his draughting skills were outstanding. Far better than mine.
We had a quick chat about his design before he started to mumble that CAD would never be able to produce drawings as detailed as his. I had to gently let him know that this statement was actually incorrect and I showed him a print of a recent drawing that I’d done that was even more complex.
The poor guys face just dropped and I could see he was absolutely gutted. I genuinely felt sorry for the guy, as no doubt he had spent a lifetime being a draughtsman, and here’s some young spotty oik producing far superior looking work.
With the advantages that CAD now brings over hand drafted drawings, as in the level of detail that can be shown, it’s more important than ever to get the line weight correct. There is absolutely no point in adding lots of detail if it’s not clear when printed out.
My personal preference now is to have the outline at 0.4mm, hatching, dimensions, centrelines, hidden detail at 0.25mm and all the fine detail at 0.18mm.
It is now becoming common not to print out drawings at all and to simply export them as PDF files. By setting up the line weights correctly the PDF drawing should look exactly how you’d like the printed out version to be.
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