How I Wasted $3,200 on the Wrong Sprockets (and What I Learned About Spur Gears)

The Day I Thought 'Spur Gear' Was a Safe Bet

It was a Tuesday in March 2019. I was a mechanical engineer handling power transmission orders for Martin Sprocket & Gear in Kansas City – or at least I thought I knew enough. One of our regular customers needed a custom assembly for a conveyor system: a ball screw actuator paired with two roller chain sprockets, and they asked a simple question: “Which gear is most likely to use a spur gear?”

“Easy,” I said. “A spur gear. It’s the most common type, right?” I’d learned that in school, seen it in countless catalogs. Not ideal, but workable. I placed the order for standard Martin Sprocket & Gear Inc parts – stock numbers all lined up, bore sizes matched the actuator shaft. Shipped from Martin Sprocket Kansas City warehouse within two days.

The Assumption That Cost Us

What I didn’t verify was the actual load profile. I assumed “same specifications” meant identical results across vendors. Didn’t check the torque ratings or the gear mesh alignment. Turned out the spur gear I selected had a pressure angle mismatch with the actuator’s output shaft coupling. (Honestly, a rookie mistake – I still kick myself for that.)

The system ran for about 40 hours before the noise started. By hour 60, one of the roller chain sprockets had visible wear on the teeth. The customer called, furious. I went on-site to see the damage: worn chain links, a bent shaft coupling, and a ball screw actuator that had lost its precision. Basically, a $3,200 order straight to the trash. Worse than expected.

“The surprise wasn’t the sprocket failure,” the customer said. “It was that you assumed a spur gear would work without checking the AGMA class.” He was right. The application needed an AGMA Class 10 precision spur gear for the torque range, but I’d chosen a lower-cost Class 8.

How Martin Sprocket’s Tools Saved My Next Project

After that disaster, I sat down with our engineering team and built a checklist. Now, before any roller chain sprockets or ball screw actuators leave our Martin Sprocket Kansas City facility, we verify three things:

• Load rating vs. application – spur gears are great for low-to-medium speed, but not for high torque at low RPM without proper rating (reference: AGMA 2001-D04).
• Bore size tolerance – we use Martin’s online catalog (martin-sprocket.com) which lists ANSI B29.1 bore standards for roller chain sprockets.
• Gear type confirmation – that “which gear is most likely to use a spur gear?” question is now always followed by “at what speed and torque?”

The automated selector tool on the Martin Sprocket & Gear Inc website eliminated the data entry errors we used to have. Cutting order processing from 5 days to 2 days. Seriously, the difference was way bigger than I expected. A lesson learned the hard way, but one that saved us a ton of headaches since.

So if you’re ordering ball screw actuators or roller chain sprockets from Martin Sprocket Kansas City, don’t assume. Use their engineering resources – they have actual technical support that knows spur gears inside out. (Wish I’d known that in 2019.)