Over the years I have been involved in the recruitment of many CNC Setters. During the interview process I will usually walk candidates around the CNC machine shop explaining what equipment we have available and the type of work we do, the examples I show them are usually accompanied by the comment “it’s not rocket science”. I am still not entirely sure for whose benefit I say it. Is it for my own in the hope that my dismissal of the difficulty will impress the prospective candidate? Or is it so that our already nervous prospect will not be put off by something he/she may see as complex or difficult?
What do we mean by “it’s not rocket science” anyway?? I guess the simple answer is that the parts are not complex or difficult to make or that conversely parts for rockets are somehow far superior to anything we make and we are simply not good enough to make rocket parts! [By 1950, rocket science was generally accepted as being intellectually difficult and outside the capabilities of the average Joe.
So how good are we? If not good enough to make rocket parts are we good enough to make parts for multipliers? I guess the simple answer is yes given that we have been making them quite successfully for many, many years including the 28 I have been personally involved. Yet we still get things wrong and mistakes are still made.
Whenever something goes wrong I am asked to investigate what went wrong and come up with a solution, a solution that will permanently fix the problem! What went wrong is not always obvious and a permanent solution is not always possible - things go wrong for many, many reasons.
So what makes a part “wrong”? As previously stated, it can be many things but generally it is a part that does not conform to the drawing specification in some way i.e. a dimension is out [of spec] or a hole or series of holes are “out” of position, the surface finish is not good enough, the material specification is wrong, or a problem with the material itself, the list goes on...
We buy expensive machines that are supposedly capable of making parts correctly; right? The simple answer is yes, we do. These same machines will be used in a Formula 1 team or Aerospace machine shop, but things can still go wrong. Let us look at what we expect these machines to do. We take a chunk of material, usually Steel or Aluminium, clamp it to the machine under a force large enough to prevent movement and then cut away material using various tools, which can all “flex” or move under cutting forces. Removing material from a part will often introduce stresses into the part causing distortion. We then expect dimensions and features to be accurate, accurate to within typically .025 mm .05 mm or to put it another way 12 thirds of the thickness of the average Human hair! In the worst cases we are asked to machine, or cut, features with much smaller allowances. These allowances can be as small as 7-8 microns (7-8 thousandths of a Millimetre) out of position in any one direction, or to put it another way 1/10th of the thickness of the average Human hair! Try splitting a hair in two never mind 10! Is it any wonder we sometimes fail.
Despite the above, we get the overwhelming majority of parts correct. We actually only scrap around 1% of parts we make. We continue to strive to make good parts, to make parts we are proud of and to make parts that are good enough for rockets!
Neil Bennett
Day Shift Manager (CNC Production)