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to incorporate alterations if we want to. See Fig. 64, which is my usual practice for small parts to be turned, the little blackboard being above the lathe. Fig. 65 is a sketch on scrap paper of part of the Davey motor. You will see that it is both numbered and dated, as it is, in fact, the only detail drawing of this part, taken off from my general arrangement. You will also see that I had

Fig. 63 A "Hand Sketch" made by the author circa 1950 using pencil in a "Sectional Book" of squared paper. Note the use of a compound sectional view. (The decimal rendering of 9/16in was due to lack of space.

Fig. 63 A "Hand Sketch" made by the author circa 1950 using pencil in a "Sectional Book" of squared paper. Note the use of a compound sectional view. (The decimal rendering of 9/16in was due to lack of space.

second thoughts part way through and altered the design, but that is another matter. Such a sketch need not be to scale, can be quite rough, but it must be complete in its dimensions. I use any paper to hand -friends in offices save me paper due for shredding and I have also had stuff from the local stationery wholesaler 'damaged in transit' - very useful I use grade B pencils, ballpoint and even felt-tip pens.

The sum up the differences, the 'idea' sketch will be the bare bones on which you will fit the detail later. It should be reasonably permanent and preferably in a book. The second type should be carefully done, as accurate as freehand work will allow, and again permanent. The third is an ephemeral affair if it is a copy of another

Fig. 64 A "Workshop Sketch" in chalk on the author's blackboard above the lathe.

drawing; this depends on what you are doing. It should be clear, the dimensions checked carefully, but the linework need not be as good as on the other types of sketch. Let us now look at the engineering drawing proper.

THE WORKSHOP DRAWING is the most familiar one, as it used to make the machine parts. It is drawn to scale, but the thickness of the lines and the subsequent reproduction processes (there may be several stages) means that it is unsafe to scale from the print itself. The prime requirement is boldness and absolute clarity, both in the way it is laid out and in the quality of the lettering and figures. It is vital that all the rules be followed, otherwise there is grave risk of misunderstanding by the machinist. This applies even if you are making the drawing solely for your own use - if, for no other reason, that you may come back to it in the future and may forget that you have taken liberties with the 'grammar'. The drawing is usually made on plain paper and then traced, but in many cases it is convenient to use semi-transparent paper from which a reasonable print can be taken even from pencil work. A medium hard pencil is used - I use 3H for centre and other thin lines and 2H for outlines, but I shall be coming to pencils shortly. In former times it was customary for all the detail parts for each component to appear on a single drawing making it rather large. Nowadays the more usual practice is to use a separate small sheet for each of the component parts -handier in the workshop and less expensive when the shop print has to be replaced. But the actual size of the drawing sheet must be sufficient to permit the various views to be laid out without crowding and to leave room for the notes which may be necessary. The drawing should contain all the information necessary for a competent machinist to make the part. In model engineering especially, there is a nasty habit of inserting a note saying 'refer to text' when a constructional article is involved. This is fair enough if the reference deals, say, with a hint on how to carry out the work; the article may be read by many who are

"Workshop " Sketch" made on scrap paper. Note the "floor to floor machining times.

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