Most drawings carry enough information that contract manufacturers can make accurate bids, says marketing manager Jack Fulton at Specialized Medical Devices, Lancaster, Pa., (specializedmedical.com). “Properly detailed drawings yield accurate bids and lowest-cost quality parts”, he says. But the rest leave his team scratching their heads trying to figure out what designers had in mind. Fulton says he sees the following drawing errors most often, and in the spirit of constant improvement, offers ways to eliminate them.

“The most challenging shortcoming on drawings are tolerances held too tightly across the board. It looks like somebody hit a default key to assign them,” he says. “Aside from being difficult to hold, tight tolerances increase manufacturing and inspection costs. However, after bringing these expensive details to the designer's attention, we can usually agree on critical and noncritical features,” he says. Tight tolerances stay on the important features and wider tolerances get applied to noncritical features, making the part less expensive to manufacture.

Another question Fulton's team asks is: Why did they specify that material? “Hardness is usually the issue. The material initially specified is often not hard enough to perform the intended function. Experience with a wide variety of metals lets us suggest a proper substitute.”

A third omission is that after finishing a design, no one looks at tolerance stack up. “If an engineer would perform the analysis, they would find their assemblies won't assemble and could make proper adjustments.”

And lastly, how components will be packaged seems an afterthought to many. Medical components often call for individual wrapping, such as in separate tubes, which means an expense the design company did not consider. Including packaging in the design avoids surprise costs, suggests Fulton.