PRIN. OF DRAFTING AND SHOP DRAWINGS - OD1641 - LESSON 1/TASK 1
3.
Freehand Drafting
In the machine shop, the sketch or freehand drawing is a quick, accurate, and clear
method of conveying ideas. Although sketching is not essential to the reading of a
shop drawing, it is helpful in learning the language of mechanical drawings.
Sketches are made rapidly and usually without the aid of drawing instruments, but
they must be accurate and complete.
Omissions and mistakes that would be
discovered in making a scale drawing might easily be overlooked in a freehand
sketch. Extreme care, therefore, must be taken to ascertain that all information
is accurate and that nothing has been omitted.
a.
Kinds of Sketches.
Sketches are divided into two general classes as follows:
(1) Class I.
Class I sketches include sketches made before the project is
started.
(a) Idea.
Used in studying and developing the arrangement and proportion of
parts.
(b) Computation.
Used in connection with mathematical calculations for motion
and strength.
(c) Executive.
Drawn by the inventor or engineer to give instruction for
special arrangements or ideas that must be embodied in design.
(d) Design.
Used for putting ideas into form from which the design drawing
can be started.
(e) Working.
Used as substitutes made from finished project.
(2) Class II.
Class II sketches include sketches made from the finished project.
(a) Detail.
Made from existing drawings or parts with complete notes and
dimensions.
They must include information essential to the making of parts, or
mechanical drawings of the parts.
(b) Assembly. Made from an assembled project to show the relative position of
the various parts, with center and location dimensions, or sometimes with complete
dimensions and specifications.
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