Designing Your Prototype, by Jack Lander the Inventor-Mentor.

Many of the inventors I work with complain that their prototype didn’t meet their expectations. In almost every case the problem is traceable to communications. The inventor didn’t design the prototype, but left a large part of that task to the prototyper.

An invention is not fully designed until you’ve created a drawing that can be used to communicate all of its features to a remotely located prototyper, and person can produce your invention without further need to contact you, and the resulting prototype is exactly as you imagined it would be.

That’s a tall order. Even professional designers don’t always succeed in creating a perfect drawing. So, how is an inventor, who is not trained as either a designer or draftsperson supposed to accomplish this ideal?

Let’s begin by looking at the differences between a “back-of-an-envelope” sketch, and a formal drawing. The sketch may show the shape of the invention, but that’s just the beginning. Here are the parameters that are often missing from our sketches.

Additional views. Conventional drawings have at least three views: front, one side, and top or bottom. If needed for clarity, the drawing may have front, back, top, bottom, right side, and left side. So, when you go to a prototyper with drawings of your invention, be sure that you present at least the three basic views: Front, side, and top or bottom. If you’re not sure what I mean by sketching or drawing these views, go to your library, and check out a book on mechanical drawing or drafting.

· Cross sections. If a feature is hollow, for example, clarity may be improved by showing a cross section. The cross section is an imaginary view of the feature drawn as though you had cut through it with a saw, separated the two pieces, and were looking at the inner surface that is revealed by the cut.

· Dimensions. Sketches may have basic dimensions, such as length and width, but the detailed dimensions are often missing. For example, if a feature is a panel of sheet metal, what is its thickness? If a hole is to be made through the panel, what is its diameter, and how far is it located from the top or bottom and from one side?

· Tolerances. Manufacturing processes are always a compromise between precision and cost. The more precise a dimension must be made, the higher the cost in most cases. Thus, the designer must tell the prototyper how much latitude or “tolerance” he may use in meeting the design dimension. For example, a large plastic part—let’s say the housing on your computer screen—will shrink as it cools after coming out of the mold. The rate of shrinkage is fairly predictable, but may vary from production run to production run due to variations in the raw material, machine cycle time or temperature, etc. Also, the dimensions are not super-critical. So an allowance (tolerance) of plus or minus .015 (approximately 1/64^th inch) might be specified for its width. The buttons on your cell phone, however, are also plastic, but must fit precisely in their openings. A tolerance of plus or minus .002, (two thousandths of an inch)—roughly the diameter of a human hair—may be specified. Generous or tight, every dimension on a drawing must have a tolerance. This is usually accomplished by having a standard tolerance for the majority of the dimensions, and only noting certain dimensions with tighter (smaller) or looser (larger) tolerances. If two parts are to be assembled, the dimensions, including their tolerances, must not overlap, which could result in the parts not fitting together. Remember, each tolerance implies a cost. Don’t specify tighter tolerances than are needed to accomplish the quality you are aiming for. For typical small parts, a loose tolerance might be .015 or .010, and a tight tolerance .005. For typical large parts, a loose tolerance might be .030, and a tight tolerance .010 or even .005.

· Materials. If your product is to be made of sheet metal, the most common metal is 1010 CRS (cold-rolled steel). This is relatively inexpensive because it is the most popular of all steels. But if you need medium hard steel, 1040 CRS may be appropriate. If you need to make a flat spring, 1095 CRS, which will have to be heat treated to achieve its spring characteristics, will be appropriate. Stainless steel is attractive because it doesn’t rust or tarnish under ordinary conditions. But it is very expensive compared with cold-rolled steel. On the other hand, it needs no painting or electroplating. Thus, small parts may be profitably made from it. There are hundreds of different plastic materials. Should you use polypropylene, polyethylene, nylon? Again, there is a wide range of costs and characteristics that must be considered in selecting the most appropriate plastic.

· Attachment. Will the various parts of your assembly be glued, stick welded, spot welded, screwed, riveted, swaged, press-fit, or snapped together?

· Surface finish. Will your product be electroplated, painted, dry coated, or left as produced (such as stainless steel)? If electroplated, will it need to be polished before plating? If painted, will it need a special paint that adheres to certain troublesome surfaces?

The above represents the basics that cover most design decisions. Use it as a check list before and after you hire a designer or a draftsperson to assure that your product is fully defined on paper. And, of course, use it if you do your own drawings.

If your part is relatively complicated, or requires an artistic touch to create an attractive consumer appearance, you may want to hire an industrial designer. If your part if relatively simple, and you have answers to the bulleted points above, you may find that you can work satisfactorily with a draftsperson. Draftspersons are usually less expensive than designers. Find these fellows under “Draftsmen” in the yellow pages.

If you decide to hire an industrial designer, be sure to find out what kind of work the firm or person has done in the past. Try to get a designer who has the kind of experience your product requires, and who works alone. The design services that have a staff are generally higher priced than the lone designer. Many prototypers are also experienced draftspersons, and may be willing to create your drawings. However, the more specific you can be about each of the bulleted items on my list above, the less expensive your drawings will be, and the more likely that you will be pleased with your resulting prototype.

* * *

Share and Bookmark:

shop4patents Blog

Comments »