Villiers engine from 1957 manual. Most anyone with the gift of a bit of talent can make CAD drawings. Obviously some are going to be real masters and some, like myself, are going to be duffers but to be able to draw the types of drawings like the one above, one would have to be truly gifted and extremely dedicated to mastering the craft. I've got several old manuals that have similar illustrations in them. I've always taken them for granted, as I suppose most people have.
I know lots of craftsmen working in a variety of trades and most of the time everything they do is taken for granted by the general public. When you drive across a bridge you normally don't think about the carpenter, laborer, iron worker, welder, painter, design engineer, cement finisher, operating engineer, teamster, and who knows who else was involved taking the bridge from design to completion. The work mostly goes unnoticed. Likewise, when it's time to repair your 60 or 70 year old motorcycle, your main concern is on fixing the bike not the drawings in the shop manual, as long as they are clear enough to help you rectify the problem all is good.
We're working with a new dividing head in my class at school. It has separate plates for different numbers of divisions that are contained inside the dividing head. The dividing head was made in Poland and the instructions are in three different languages. Not the clearest of descriptions in the Polish to English translation, but the exploded drawing makes things quite clear as to how it goes together and what the plate looks like thanks to a skilled technical illustrator in Poland.
I've been involved in technical education for over forty years. I don't think I've ever heard anyone promote the field of technical illustration to a student, unless it came from inside the cover of a matchbook. No technical illustrators showed up on career day. Most all schools used to offer board drafting to the boys along with some metal and wood shop - home economics for the girls. Drafting was offered because every trade uses blueprints and you could get a job as a draftsman. Technical illustrator? Just one career out of probably hundreds that never was mentioned or promoted as an option that at least a few students could have pursued and done well at.