Ask the Expert: Shop Floor CMMs

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by Kip Hanson 

Coordinate measuring machines are only for the inspection room, right? Maybe not.

I can name several shop owners and quality control people who would call me crazy (or worse), but I’m a big fan of putting coordinate measuring machines (CMMs) on the shop floor. I’ll offer some good reasons to do so in a minute, but let’s start by addressing the naysayers’ objections. 

The first is temperature. Everyone knows that shops should keep their metrology labs at 20°C (68°F). And although I don’t have any real desire to spend the $509 for the ISO 1:2016 “Geometrical product specifications (GPS) — standard reference temperature for the specification of geometrical and dimensional properties” document, I’m pretty sure there’s something in there about humidity control as well. 

Such cool, dry air would be nice for the people who work on the production floor, but unless they’re making ultra-precision widgets for a local university or the Royal Canadian Navy, it’s simply not feasible for most machine shops and sheet metal houses. 

CMMs are also quite expensive, especially for a machine that, as many shop owners like to point out, doesn’t produce anything. As with air conditioning on the production floor, what shop can afford to buy more than one or maybe two of them? 

Lastly, they’re delicate, with precision air bearings and long, spindly touch probes. Just as everyone knows that CMMs should be kept in temperature and humidity controlled environments, they also know that shop people are tough on equipment. Right?

Wrong on all counts. Set aside any concerns over costs and equipment usage for a moment and consider the following scenario: In my fantasy machine shop, the CNC machinist will not have to take her first article to the QC room and wait until buy-off before beginning production. Nor will she break the rules, as I once did and not
wait for inspection, taking full responsibility for any resultant scrap.

Instead, she will set the part on the CMM, scan a barcode on the job traveler to call up the correct inspection routine, and get busy measuring the part. And if the CMM is automated, so much the better. Now we’re looking at two to three minutes of lost time rather than the 20 minutes to an hour that parts might linger in the traditional inspection queue, during which a CNC machine tool that costs way more than a CMM sits idle. 

Nor are the objections over a CMM’s supposed fragility or temperature sensitivity realistic. I’m not naming any names, but there are all manner of shop-hardened CMMs, vision machines, and so-called comparators or “gauging systems” available on the market today, many of them at an easily-digested
price point. 

These systems are also getting easier to operate and, as noted earlier, can be programmed in advance so that even less experienced personnel will have no problem performing a first article inspection. Installing a few of these on the shop floor or marrying one to each CNC machine tool might seem like overkill, but is actually a reasonable approach to maximizing productivity and part quality alike. SMT

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