Drawing and sketching

Drawing is the common language of metalworking professionals. Except for minor differences in conventions, two metalworkers in different countries should be able to exchange drawings and be able to interpret the specifications. This ability to communicate across language barriers is extremely powerful. 

Use 8½ "×11 " sketch paper, draw large and fill the sheet. Tiny sketches are like tiny brains: who wants one?

Press hard with the writing instrument. Faint lines and text are for accountants—not metalworkers. Everything shows up when the sheet goes through the copier if you use a heavy hand.

Take some time and learn how to functionally sketch in the isometric projection. This technique saves countless hours of drawing time because many times you only need one view instead of the standard two or three views to fully communicate a part.

The three isometric axes.

I have a little trick to help me with my isometric drawing. I made a special ruler, which, when combined with normal graph paper or even plain lined paper, can make anyone’s isometric drawings look good. Although you can buy ruled isometric paper, I found that when you photocopy or scan it, the grid lines get darker and you wash out your sketch object lines, turning a nice isometric sketch into a jumble of spidery lines.

To start making decent looking isometric sketches on the shop floor, you will need a plastic ruler that’s clear so you can see through it. It should have lines on it parallel to the long axis of the ruler. These are used to set distances parallel to existing lines. They also work great for spacing hatch lines when you draw a cross section.

If you want nice circles, you will need an isometric circle template. I skip the template in the shop and hand draw circles. Remember that the goal is to get it done as quickly as possible with good quality. It’s better to have a decent quick sketch than a perfect sketch that took way too long to make.

The Iso-ruler I made is cut off at the same angle, approximately 35°, as the normal isometric axis. 

When drawing to scale, the three isometric axes are the only directions that measurements can be made along. With the Iso-ruler, you can align the angled edge with the vertical gridlines of normal graph paper or even the edge of the pad itself. Flip the angled edge over and you have an alignment guide for the opposite direction. I like the engineering pads that have the lithographed grid on them for anything I run through the copier. The lines are a faint green and disappear in the copier.

With the parallel lines on the ruler, you can set off distances quickly by sighting through the clear ruler. This is a simple method for drawing quick, concise job sketches. It’s better to have some kind of sketch even if it’s not technically perfect because you can’t do this stuff purely from memory.

When sketching quickly, try to get the scale and proportions roughly correct. They don’t have to be deadly accurate; they just need to look about right. If a part is long and skinny, sketch it that way.

Learn and use the basic rules of drafting. These rules and conventions have been refined over hundreds of years. You can bend them a little, but don’t break them into a million pieces.

Some of the major abuses I see in electronic drafting are incorrect line weights, omitting hidden lines in views, mission dimensions, incorrect third-angle projections, lazy details on hole bottoms and thread misrepresentations. These abuses result from ignorance of drafting conventions and laziness. Just because you can draw something with an expensive electronic drawing program does not mean you are doing it according to established conventions. As the saying goes, garbage in, garbage out.

Avoid the temptation to use an electronic drafting or modeling program immediately on a new design. In the earliest stages of a design, CAD is often a hindrance or waste of time. CAD promotes a microscopic view with way too much detail and precision in the opening stages of a concept’s development. This weakness, coupled with the possibilities of countless revisions and iterations, can make CAD a serious time liability. If you can’t get the concept down with paper and pencil, you have no business behind a computer’s mouse.

Date and initial all your hand sketches and keep them in a binder. Having these handy has saved me many times. Always release a copy to the shop and retain the original information as a backup. CTE

About the Author: Tom Lipton is a career metalworker who has worked at various job shops that produce parts for the consumer product development, laboratory equipment, medical services and custom machinery design industries. He has received six U.S. patents and lives in Alamo, Calif. Lipton’s column is adapted from information in his book “Metalworking Sink or Swim: Tips and Tricks for Machinists, Welders, and Fabricators,” published by Industrial Press Inc., New York. The publisher can be reached by calling (888) 528-7852 or visiting www.industrialpress.com. By indicating the code CTE-2010 when ordering, CTE readers will receive a 20 percent discount off the book’s list price of $44.95.