A few years ago, I did some consulting and training for a manufacturing company. Components of their products were made from metal castings with some precision requirements below a thousandth of an inch. The company had some trouble achieving these tough product targets and I was there to help.

Now put yourself in the management of this operation as you read, and ask yourself, "What would I do?"

All of the metal components were machined according to mechanical drawings. ("blueprints".) After some research into the prints I made an interesting discovery. Many of the prints had a common flaw. (Let me simplify the story here to help you make a mental picture.) Imagine that a hole is to be drilled into a eight inch wide block of metal and the drawing calls for the center of the hole to be exactly four inches from the left edge and five inches from the right. Now, make the mental picture. Do the math! See the problem?

The drawing is ambiguous. There are two possible places that the hole could be formed. Errors of this sort are avoided in drawings by specifying all dimensions from a single common reference. The engineering drawings had many of these errors, and I brought this to the attention of management.

Now, if you were responsible for managing this company, what would you do?

I further researched the machining processes and found a long row of machining work centers . Each work center  made one or more cuts into a rough metal casting and finished parts were produced at the end of the line. This "pipeline" approach had tremendous potential to rapidly turn out quantities of product. Once configured for a certain specific part, this "assembly line" approach to metal machining was extremely productive.

Everyone knew that the first machining work center  was extremely critical. It made the "reference" surface. This is the same principle in the handling of materials as in drafting. The first cut created a smooth flat surface on the cast iron part. Every subsequent act of positioning and measuring that specific part for the rest of its manufacture began with lining up that flat reference surface to a known position mark.

The problem was this: the finished parts came out different. Statistical analysis showed four distinct groups which were traced back to a casting "mark" of 'a', "b', "c", or "d". The molds for the iron castings formed four parts at a time. Parts that came from mold 'a' were very much like any other "a", but different from "b". The difference was small, but enough to produce significant scrap.

I recommended that we add one work center to the start of the machining line. The job was simply to -sort- the castings by mold. Castings marked 'a' would be processed and then the cutting machines would be recalibrated before 'b' parts would run. We did an experiment. We tested the sorting station theory. Setup time was dramatically reduced because first piece QA checks came back on the money and without delay. Every part now left the first machining work center with a consistent reference surface, and the finished parts came out as "same" (plus or minus) and not as "four flavors".

Now, after this little experiment succeeded, if it were your facility and your money, what would you do?

Finally, there was a third story to tell  from this plant. it is a story that I have told in some detail elsewhere, but here is the abridged version. A work center was designed as a round turntable. Seven stations with cutting tools were arranged around the table, and the eighth station was a standing position for an operation to attach and remove parts from the table. The operator would unload a finished part, load a fresh part, and then start the cycle. The table would rotate 45 degrees and each of the seven machining stations would go to work on their respective parts.

The machine had a terrible reputation with the operators and no one wanted to be responsible for setting it up for a different kind of part. After some investigation, I found out why. The two stations on either side of the operator and the center of the table were designed to form  a perfect 90 degree angle for reference and measurement. All placement of fixtures on the table and all positioning of the remaining five stations were to be made from this objective and absolute frame of reference.

I discovered that someone had unbolted and moved one of the two reference machining stations in an attempt to set up the machine. The perfect right angle was broken and a 91 or 92 degree angle had taken its place. It was now -impossible- to perform precision machining at this work center. The only solution was to reposition the two critical stations relative to the center of the table, and this required the machine maker's assistance and precision laser measurement tools.

So once again, if it were your responsibility, what would you do?

Here is the rest of the story.

Regarding the blueprints: the company decided to do nothing. Regarding the new pre-sort work center: The company decided to do nothing. Regarding the machine damaged by an untrained setup operator: the company decided do nothing, and to leave the machine at it was.

The next time your engineers, plant managers, training or quality personnel tell you "we did SPC, measurement studies, process management, all those things...and they didn't make a difference in our scrap rate." - take that with a big grain of salt, and get the rest of -their- story.

If you do what you always did, you'll get what you always got.