Machine Sketching

By | March 13, 2017

The first purpose of a drawing is to give a clear idea of the shape of the pieces wanted with it’s dimensions. While a well executed drawing with smooth lines and nice shading makes a pretty picture, it may not be nearly as useful as a rough sketch that has every dimension correct. The sketch may not show everything in its true proportion, but if the numbers are right, no one should be misled as there is no excuse for measuring a drawing when all the dimensions are given. One of the best things to do for practice is to sketch any tool or object around the shop, such as the anvil, a lathe dog, pair of calipers, a pulley or a hacksaw frame, so as to be able to make a new one just like the other. This teaches us to be careful to put down all the changes of shape and all the dimensions and to be careful that the figures are right.

Take a plain bolt or nut, sketch it so that you can put the dimensions on the right places and just about anyone can read them. For this purpose some sort of a perspective view is best. This can’t be done with complicated pieces, but for simple stuff, it’s easy to make something that’s often more understandable than a regular drawing.

In Fig. 1, There’s no need to make circles perfectly round or lines perfectly straight. We only to give the idea of the general shape of the piece needed. Anyone who could make a mistake in making bolts from this type of sketch has no business working in a machine shop. This shows the bolt to be 4 inches long under the head with a 13-pitch, United States standard thread cut 1-1/2 inches on the end. The bolt is 1/2 inch rough, hexagon head, 1/2 inch thick and 1-1/8 inches across the flats, but not finished.

Don’t be afraid to put any information necessary on the sketch or on any drawing. It’s better than leaving a lot to the imagination as some drafters seem to like doing. It’s a good idea not to put the same dimension on twice in different places because there’s a chance of getting one of them wrong, which makes confusion. Have the sketch tell all it can either by figures or notes; it can’t give too much information.

Fig. 2 is a steel gauge, 1/4 inch thick all over, 2 inches long in the main part, with the end projection 1/2 inch each way, a 1/2 inch corner as shown and the round corner with a 3/4 inch radius. The fillet (rounded area) is not important as long as it’s rounded out enough to prevent cracking while it’s hardening.

Fig. 3 shows a small connecting rod, 24 inches center to center, which is the important dimension. The hole at the left is 2 inches in diameter and at the right it is 3 X 4 inches for an adjustable box. This opening is shown divided each side of the center so that the total length of the rod will be 24 + 2-1/2+ 3 = 29-1/2 inches. The ends are 2 inches thick and the central portion is round, 2 inches in diameter.

Making sketches is also great training in another way. It teaches us to observe little details. Most of us look at an object without seeing more than the basic outline. To test this, lay twenty common articles on a table or bench, ask a man to look at them for a full minute and then go away and make a list of them. Seems easy, of course, but just try it yourself and see how much easier it is to forget from quarter to one-half of them. But in making a sketch, we have to note the details and then remember them.

One more time, let me remind you of the importance of not forgetting any necessary dimension. It may not matter much if you can go and take another look at it, but it’s a different proposition when you are sent off a few hundred miles to sketch a broken piece and find some dimension is missing. I guarantee you’ll feel dumber than a box of rocks and you can just about imagine the snide remarks the boss will be making to himself ,even if he doesn’t say it out loud.

One thought on “Machine Sketching

  1. Katia Young

    Very good observations here on the importance of sketching your pieces. One thing I would like to add – and it’s something you touched on – is the importance of taking the time during rough sketching to identify & get the location right of any crucial details that could be missed, or misrepresented later on.


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