In the small world of 3D metrology, we all have heard the same questions in various contexts countered with some wildly different answers. This new column will explore these frequently asked questions, and address what is and what is not proper 3D metrology practice. Over the coming months, I will cover topics ranging from calibration to lasers to everything in between. The read will be quick, concise, and hopefully enjoyable, with the end goal of moving metrology conversations in the right direction.
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My name is Shaun Wissner. I have been at this metrology gig for more than 15 years, working in nearly every position in this field from quality technician to manager in various industries. It was in the mid-nineties, when I was working in the light machinery industry, that I was introduced to my first coordinate measuring machine (CMM), a nice little tabletop manual machine with MicroMeasure III software. Then I got into foundry work (hot iron and aluminum) where I got my hands on a couple of automatic CMMs, much nicer than the manual unit but way more complicated and breakable.
At present, I am an applications engineer at Hexagon Metrology. To put it plainly, I’m “traveling technical support” for any type of computer-aided measurement device and software. In this capacity, I work very closely with clients to understand their unique applications and their measurement problems. It is my job to respond to their questions and find the optimum solution. I am anxious to share what I have learned from working face-to-face with customers, and with the help of some industry experts, lay it out for you in plain English.
The two big problems
So, back to the point about moving metrology conversations in the right direction.
There always seems to be two big problems when talking to people about the science of metrology. First, and probably most obvious, is terminology. I am not infallible in this regard. To this day I will use the phrase “probe calibration” when I should say “tip qualification.” That is to say, there is no such thing as “probe calibration.” In this context neither the word “probe,” the part that actually triggers the hit, nor the word “calibration” is correct. As insignificant as this sounds—everyone hearing those words can most likely infer the proper meaning with some follow-up information—this little mistake will compound itself as the conversation continues, leading to the wrong questions and probably the wrong solution.
Just to be clear, the CMM, as in the entire integrated system, is calibrated to a prescribed specification using known artifacts, environmental variables, laser sensors, and mechanical adjustments. The tip, which makes contact with the actual part, is simply qualified (not calibrated) against its nominal value to remove its inherent inaccuracy. Most CMM styli, or tips, are certified for roundness, not size, so a qualified size value is required for the system to achieve its specified accuracy and uncertainty when measuring, well, anything really.
The second issue is industry trends. Every time some new technology comes out everybody just has to have it. But, just because your competition is doing it, it does not necessarily mean you should, too. There is a great divide between doing things and doing them well. For instance, right now laser scanning is hot. Everyone wants their parts scanned with a laser because more data must be better, right? Well, not always. Sometimes more is just more.
Hopefully, I have piqued your interest enough to check out my column next month where I will start to dig into the difference between data collection and data management. This is a broad topic, so in order to keep it readable, I will cover it over a few columns depending on your feedback. That’s right, this column is interactive and I’ll be “probing” your comments on-line. If there is any topic bugging you (in the sphere of metrology only please, as I’m not qualified to give relationship, medical, religious or political advice), let’s talk it out, point by point.
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