How to keep from scrapping parts

Scrap happens. By scrap, I mean parts that are out of tolerance and, therefore, useless.

Scrap is the physical manifestation of a wasted machining effort. Unlike other by-products of the manufacturing process, such as chips, shavings and drops (the last bits of bar stock that are too short for making parts), you generate scrap only through mistakes.

So the challenge of reducing scrap comes down to preventing mistakes.

Step one of not making mistakes is to, counterintuitively, make mistakes. Step two is to learn from them. After generating scrap, document exactly what mistakes were made and how they could have been avoided. Then require new trainees to read these comments as part of their training. Smart people learn from others’ mistakes and don’t make the same ones.

I’ve learned to minimize scrap because of making lots and lots of mistakes. Presented here is some of what I’ve learned so that, hopefully, others don’t repeat them.

Few things waste more time in a shop than performing secondary operations on a part that should have been scrapped after the initial operation. Obviously, there’s no “best” time to scrap a part. But if there were, it would be during the design phase. For all jobs, even one-offs, make a complete plan—including drawings of all dimensions, fixtures and processes—before you remove any material.