A drafter (draftsman) is required in most cases to draw from rough freehand sketches, made by themselves or by someone else either from an actual object or an imaginary one. For instance, suppose that a machine is in operation somewhere and the drawings never existed or were lost. For the purpose of rebuilding or regularly fabricating this machine or part, a set of working drawings is needed. Suppose the machine is in a place that it is not easily accessible to the drafter all the time so that they can’t take measurements while making the drawing. In such cases they have to make sketches which are rough mechanical drawings, drawn freehand which are later turned into regular technical drawings on the drafting board or in CAD.
Suppose a certain change or modification has to be made to a machine, machine part, or mechanism or even a new one has to be fabricated. If so, a working drawing is going to be needed. The idea is then made clear to the drafter by means of sketches more or less complete, which the regular drawings are eventually created from.
A sketch has to have all the essentials of a working drawing except that it isn’t to scale, although the relative proportions of the object represented are maintained as near as this is possible by mere eyesight. As in a mechanical drawing, the sketch must clearly contain all the dimensions and notes needed to make it possible for the object to be fabricated from it. In all intents and purposes, a working sketch could be immediately be used as a working drawing and is sometimes is in cases of emergencies.
A regular working drawing however, is generally more elaborate lot only is it drawn to scale, but generally a smaller number of views of the object are shown than are required in a sketch. In both one endeavors to get along with as few views as are necessary to clearly represent the object, although in a sketch, a multiplicity of lines is avoided by additional views and sections, which can be quickly drawn; also, various notes, short cuts, and conventional marks may be used more freely on a sketch than would be tolerated on a regular drawing.
The procedure for making a technical sketch is first fully represent the object in as many views as necessary to bring out all the details; the measurements are taken afterwards and are written in. This is really the best way, as lots of time can be wasted by trying to take measurements and write dimensions as one sketches. Furthermore, by first fully completing the sketch a better general knowledge of the object is gotten, which will help in distinguishing between dimensions that are essential and those that aren’t.
All that’s really needed for making a sketch are a lead pencil, grid paper and a good eraser. The paper is best used in letter size, 8 1/2″ x 11″ in pads of 100 or more sheets that the single sheets can be detached one by one. The paper should be heavy, so that it will stand considerable abuse; Manila paper is very good for the purpose. Grid paper is well adapted to sketching; the little squares are a great aid in enabling the piece to be sketched in proper proportion and assist materially in producing rapidity. The kind that is divided into 1/4″ squares is the best but smaller can be used. If you are just learning to sketch, I advise you not to use it until you have become proficient in making sketches on plain paper, since in actual practice you will often be necessary to make sketches on plain paper, and you will find it very difficult to do this if you have not learned to depend on grid paper.
To learn more about Machine Sketching, please go to The Online Drafting School at http://draftingschool.net/