Monday Morning, Q1 2025
A pallet of Renishaw linear encoders arrived at our dock. Fifty units, shrink-wrapped, labeled with our PO number. I’d been reviewing incoming inspection results for four years at that point — roughly 200 unique deliveries each year — and something about this batch felt off before I even opened a case.
Our supplier had quoted a price that was 12% lower than our previous vendor for the same Renishaw encoder model. At the time, my procurement manager said, “Great deal.” I said, “Let’s see what’s inside.”
The First Red Flag
I pulled out my Starrett micrometer — a 0–1″ unit I’ve used since 2022, when I implemented our dimensional verification protocol. If you’ve never used a Starrett micrometer, here’s the quick version:
- Clean the anvil and spindle with the paper included in the case
- Close the micrometer until it lightly contacts the object — use the ratchet stop, never force it
- Read the sleeve (0.1″ per revolution) and the thimble (0.001″ per division)
- For this job, we needed ±0.0005″ tolerance
The first encoder body measured 1.2380″ on the Starrett. Spec says 1.2370″ ±0.0005″. That’s a 0.0005″ oversize — barely, but out. The second unit? 1.2385″. The third: 1.2390″. By unit ten, I had data that screamed systematic drift.
So I grabbed our Mitutoyo point micrometer — a set with a 0.3 mm radius tip — to check the mounting surface flatness. Point micrometers are great for measuring small grooves or shoulders, but here I used it to detect local deviations on the encoder faceplate. The results were worse: some spots were 0.001″ lower than the nominal surface.
Then I Brought Out the Ultrasonic Sensor
Our Panametrics ultrasonic thickness gauge (a 38DL Plus) can detect internal voids or delaminations. I applied couplant and scanned the encoder housings. Two units showed a 2.5 dB drop in the backwall echo — indicating a possible inclusion. That was enough to reject the entire batch.
Everything I’d read about Renishaw encoders said the brand was bulletproof. In practice, this particular lot — sourced through a distributor undercutting the market — had substandard material. The conventional wisdom is that a brand name guarantees consistency. My experience suggests otherwise: the source and the price are the real indicators.
It took me 3 years and about 150 inspection orders to understand that lowest-bid pricing often hides the cost of rework. The buyer who lists all fees upfront — even if their total looks higher — usually costs less in the end. Because when a $3,000 Renishaw encoder fails because of a 0.001″ machining error, the downtime on a $150,000 CMM is what really hurts.
The Rejection and the Lesson
I formally rejected the batch. The distributor claimed we were being too strict — “within industry standard.” But our internal specification (based on Renishaw’s own published tolerances for linear encoders, per their technical datasheet) required tighter. We stood firm. They redid it at their cost, using a different sub-supplier.
Here’s what I’ve learned: trust isn’t built in the sales call; it’s built in the quality review. The supplier who voluntarily shares their inspection data upfront — even data that shows a few units slightly out of spec — earns more credibility than the one who hides behind a low price. Per the FTC’s Green Guides, similar logic applies to truth in advertising: claims must be substantiated. That applies to metrology products too.
So if you’re specifying a Renishaw linear encoder, or any precision component, don’t just compare unit prices. Ask: “What’s not included?” and “How will you verify before shipping?” I’ve learned never to assume the proof represents the final product — not after that batch.
Bottom line: a point micrometer and an ultrasonic sensor can save you a lot more than they cost. Use them. And for your next hundred parts?
“The vendor who shows you their rejects is the vendor you can trust.”
