A FARO Laser Tracker, a FARO Arm, and the $42,000 Lesson About Humidity

How the FARO Laser Tracker Entered My Life

I've been handling precision measurement equipment orders for nine years. In that time, I have personally made—and documented—eleven significant mistakes. Add it up, and I'm looking at roughly $42,000 in wasted budget. That number includes rework, expedited training, and one very expensive return that I still don't like to talk about.

Back in 2022, our shop signed a contract to verify large aluminum frame assemblies. The biggest fixture was about fourteen feet long, and the customer wanted a dimensional report with a tolerance of 0.005 inch. Our stationary CMM could not handle parts that large. So I did what a lot of equipment buyers do: I built a spreadsheet, compared laser tracker specs, and asked my manager for a FARO laser tracker. He approved it faster than I expected. That was the first red flag I missed.

From the outside, buying a portable measurement system looks like a hardware purchase. The reality is that you are buying a measurement process. The FARO Laser Tracker is a serious instrument. Ours is still running today without a single major repair. But the damage I caused in the first year came from treating it like a tool that would work no matter where I plugged it in.

Lesson One: The Tracker Needs Training

I skipped the optional training. It cost $2,800, and I thought we could learn by doing. On the first morning, I could not get the tracker to hold a stable base coordinate. FARO support asked me what I was using for a reference, and I said 'the floor grid.' There was a pause on the call. That pause was the sound of a budget error. I ended up paying $4,600 for expedited on-site training a week later.

The training was worth every dollar, but here is the part that still stings: the operator manual and my own stubbornness caused the delay. Nobody on the FARO support team was rude. They were professional. I was the one who thought I could skip the basics.

CMM FARO Arm Measuring Machines Are Not a Substitute for a Process

The next request came after we realized the laser tracker needs line of sight. We had to inspect internal features on a box weldment, and the tracker could not see inside. That is when people search for CMM FARO arm measuring machines. We bought a FaroArm. It solved the line-of-sight problem, but I made the same mistake again: I trusted the spec sheet instead of the process.

The arm's repeatability looked great on paper. On the shop floor, the readings changed between 8 A.M. and 3 P.M. in July. We were not measuring the part; we were measuring the thermal expansion of the air and the aluminum. I blame myself, not the equipment. The arm eventually found a permanent home in a temperature-controlled inspection room, where it works beautifully. Its annual verification follows ISO 10360-12, which is the standard for articulated arm CMMs.

The Twist: A $40 Hygrometer Almost Cost Us a Week

Then came the problem that made me look foolish for a month. The tracker's measurements on the large frames started drifting. No pattern. One day good, the next day off by almost 0.008 inch. We checked the part setup, the software, the operator. All fine. I even questioned the technician's technique—unfairly, by the way.

FARO support finally asked a simple question: 'What's the humidity in the room?' I pointed to the cheap hygrometer on the shelf. It said 42%. They asked me to verify it. I put it next to a calibrated hygrometer. The cheap unit was 26% off. The actual humidity was 68%.

People think a laser tracker measures distance. The reality is that it measures through air, and the air's refractive index changes with temperature, pressure, and humidity. ASME B89.4.22 (the laser tracker performance standard) treats environmental monitoring as part of the test process. I had read that standard. I still ignored the environment.

That same week, support asked me to check the electrical supply. I grabbed the clamp meter 323 from the maintenance cart—the model a lot of plants own because it is inexpensive and good enough for basic current checks. The meter was fine. The reading was not. We saw a six-volt drop every time the air compressor kicked on. It wasn't enough to damage the tracker, but it was enough to make the controller lose its mind occasionally. So we had two invisible problems at once: humidity and power quality.

Starrett vs Mitutoyo Digital Calipers: A Smaller Mistake With the Same Lesson

In the middle of this mess, our supply clerk asked me to approve a caliper order. The machinists had opinions, and the old debate started again: Starrett vs Mitutoyo digital calipers. I have used both, and I genuinely like both for different reasons. The Mitutoyo IP67 coolant-proof model is the right choice for our CNC area. The Starrett calipers have a nicer thumb wheel and feel better at the inspection bench.

The bigger lesson is not which brand. It is consistency. A few years earlier, I approved three pairs of mixed-brand calipers for the same inspection process without checking calibration first. They all measured the same gage block differently at the 0.001-inch mark. We caught it before any parts shipped, but only because a machinist happened to measure the same block with two tools. That order cost $890 in calibration and replacement work. The incident is why every caliper we buy now goes to an accredited lab for NIST-traceable calibration before it touches a part.

The Checklist That Finally Stopped the Bleeding

After the third rejection in Q1 2024, I created our pre-check list. It is not elegant. It is a printed sheet that hangs next to the tracker's case. The full list has twelve items, and it looks obvious in print. It was not obvious in the moment. Here is the condensed version.

• Check temperature, humidity, and pressure against the manufacturer's allowed range.
• Verify the hygrometer and thermometer against a calibrated reference.
• Check power quality at the same outlet you will use for the measurement system.
• Run a length measurement on a calibrated artifact before every shift.
• If using an arm, zero it and measure a known feature first.
• Record the environmental numbers on every inspection report.

This list has saved us an estimated $8,000 in potential rework over the last eighteen months. The math is simple: 5 minutes of verification beats 5 days of correction.

The FARO laser tracker was never the problem. CMM FARO arm measuring machines were never the problem. The problem was my assumption that expensive hardware removes the need for a careful process.

Now we budget for training, calibration artifacts, environmental sensors, and a little time to do the checks. It is not the most exciting way to spend money. But it is a lot cheaper than the way I found out.