Freehand sketching is an important skill in connection with drafting. When we use the term sketching, it shouldn’t be considered as an incomplete drawing however. If anything, a sketch needs to be more complete than any mechanically executed drawing. Sketching is the engineering language of the trained engineer and drafter as well as a convenient and quick method of graphical representation. Sketches are used to give information from which parts are made; they’re used for repair parts; new parts; as an aid to reading drawings; as an aid to design; as a means of recording ideas, and a great many other purposes.
Accuracy of thought, observation, representation, and proportion are essential.
The 4 “P’s” of sketching are:
You can’t put too much emphasis on accuracy in proportion and detail.
A very interesting example is shown to the left that’s a reproduction of a sketch for the first steam hammer, drawn by James Nasmith. (click on image to enlarge) Quoting from Nasmith’s autobiography by Samuel Smiles: * “I got out my ‘scheme book,’ on the pages of which I generally thought out, with the aid of pen and pencil, such mechanical adaptations as I had conceived in my mind, and was thereby enabled to render them visible. I then rapidly sketched out my steam hammer, having it all clearly before me in my mind’s eye. In a little more than half an hour after receiving Mr. Humphrie’s letter, narrating his unlooked-for difficulty, I had the whole contrivance in all its executant details, before me in a page of my scheme book. The date of this first drawing was November 24, 1839.”
Materials for Sketching
The materials necessary for sketching are a 2H drawing pencil, pencil eraser, art gum, and paper. Either plain or gridded paper may be used, but it’s better to use the plain paper at first so you aren’t as dependent upon the aid that the squares give. The pencil should be kept sharp with a long round point. It’s a good idea to have a clipboard for a solid backboard for the paper. Every sketch should have a title, the date, and the name of the person who made it.
To the right is a sketch I made of a steel plate connection. (click on image to enlarge) To make a sketch, try doing things in the following order.
- First examine the object, determine the number of views necessary to completely to define it, and observe the proportions.
- Then proceed to sketch very lightly, locating center lines and blocking in the limits for all views.
- Sketch in the details and then go over and brighten up wherever necessary in order to make all parts clear and definite.
Straight lines may be drawn by making a succession of short straight lines or by marking points and drawing from one point to the next. Views should be blocked in completely with straight lines regardless of the number of curves and circle arcs.
To sketch a circle, draw center lines at right angles (Fig. “A”), space off the radius, as shown in Fig. “B”, on the center lines and in between them. Another method is to block in a square made up of four smaller squares (Fig. “C”), then sketch in one fourth of the required circle at a time.