Thomson-Linear Bearings Checklist: 6 Steps Before You Order Linear Motion Components

For eight years, I've been the guy at Thomson-Linear who gets the orders that don't quite make sense. The actuator with no load specified. The linear bearing that's somehow too big and too small at the same time. And the occasional request for ball bearing casters—which, by the way, we don't make. More on that later.

I've personally made and documented 46 significant mistakes in the last eight years. That's not a flex. It's about $38,000 in wasted budget, rework, and expedited shipping. This checklist is the one I wish someone had handed me in 2017.

Use it when you're picking thomson linear bearings, linear actuators, motors, or any other piece of a linear motion system. Six steps, in the order I do them. Most people skip Step 5, which is probably why I see so many of the same problems.

Where this checklist came from

Back in 2019, I approved a rush order for 30 linear bearings. The shaft size matched, the stroke was fine, and the load "seemed okay." What I didn't verify was the motion profile—acceleration, duty cycle, the whole machine context. We didn't have a formal motion profile review process then. It cost us when the bearings showed up and couldn't handle the actual cycle. $3,100 in parts that couldn't be returned, plus a week of delay while the customer waited.

I built the checklist the next Monday. It's changed a lot since then.

Step 1: Write the motion profile before you open a catalog

Here's the thing: nobody orders a linear bearing for fun. It's there because a machine needs to move a load in a specific way. If you don't write that down, every number in the catalog is just a guess.

What I mean is, you need more than "it moves a box from A to B." You need the mass being moved, orientation, stroke length, cycle time, acceleration, deceleration, position accuracy, and how many cycles the machine runs per day. Put that on one page. Show it to the vendor. It catches more errors than anything else I do.

In 2021, I compared two orders side by side—same actuator, same stroke, but one had a 2-second cycle and the other had a 30-second cycle. The difference in required life was enormous. That's when I finally understood why the motion profile isn't just paperwork. It's the whole job.

Step 2: Make sure everyone means the same thing by "ball bearing"

Let's go back to a basic question: what's a ball bearing? Basically, it's a set of balls running between an inner and outer ring. The balls turn sliding friction into rolling friction, so a load can move smoothly with less force. In linear motion, we use ball-based rolling bearings too, like thomson linear bearings, where the balls roll along a shaft or rail.

The word "bearing" is doing a lot of work there. A ball bearing caster, for example, has ball bearings inside the wheel and the swivel, but it's not a linear motion component. It's a wheel-and-housing assembly that helps carts move around a floor. Different product. Different engineering. I've had customers ask us for both, and honestly, I'd rather explain the difference upfront than send them something useless.

Step 3: Load ratings are not decorative

I once chose a linear bearing based on its dynamic load rating alone. It fit the shaft, had plenty of life on paper, and the price was good. Then I realized I'd ignored the static load rating—the load the bearing could handle while standing still. One machine crash later, the bearing was dented. The static rating had to be above any short-term spike, not just the steady state.

Now I check three numbers: dynamic load, static load, and life. In that order. The life calculation is usually a formula that includes load and distance traveled. According to ISO 281, the basic rating life of rolling bearings depends on the dynamic load rating and the equivalent bearing load. I'm not going to pretend I can do that math in my head—that's what the spreadsheet is for. But if a supplier can't tell you the dynamic and static rating for their thomson linear motion component without checking, that's a red flag.

Step 4: Match the motor to the machine, not the other way around

Motors are a place where I see people get stubborn. A stepper motor is good for simple positioning. A servo motor is better when you need closed-loop feedback and higher speed or torque control. And an ac motor? It's the workhorse for continuous rotation—pumps, fans, conveyors running at constant speed. Pick the motor that fits the machine's real job, not the one sitting in a drawer.

In 2022, a customer asked for a linear actuator with an ac motor because their plant is all 3-phase and they wanted one spare part for everything. But the operation needed precise stops at multiple positions. The ac motor could do the speed, but it couldn't do the positioning without a lot of extra hardware. We ended up changing to a servo-based thomson linear motion system, and the machine worked. The lesson wasn't "ac motors are bad." It's that the motor has to match the motion profile from Step 1.

And if a vendor says "one motor does everything," be careful. That's usually a compromise that does nothing perfectly.

Step 5: Verify the mounting details (the step everyone skips)

This is the one that hurt. In 2020, I ordered 40 thomson linear bearings with the right inner diameter, right load rating, and right seal material. What I didn't check was the bearing's external dimensions against the housing on the workbench. It didn't fit. Forty pieces. $1,850. "Can't you just machine the housing?" Sure. But that wasn't in the budget or the schedule.

Now I treat drawings as a question, not a suggestion. Get the shaft tolerance, the housing bore tolerance, the recommended fit, and the mounting surface flatness. "Standard" means different things in different catalogs. Look, the people who say "trust me, it's universal" are usually the ones who haven't seen your drawing.

Step 6: Ask for numbers, not adjectives

"Heavy duty," "industrial grade," "high performance." Give me a number. Give me test data. A good technical datasheet tells you the rated life in meters or cycles, the maximum acceleration, the IP rating for dust and water, the temperature range, and the lubrication interval.

The one thing I never ask anymore: "Is this the best product?" Of course the salesperson will say yes. Instead I ask: "Where is this product going to fail first? What's its weak point?" If they can't answer that, they haven't tested it. If they say "it won't fail," that's not engineering. That's a marketing sentence.

One more thing: know what your supplier actually does

Remember the ball bearing casters I mentioned at the start? We don't make them. That's not us being modest. Thomson-Linear specializes in linear motion: linear bearings, actuators, ball screws, motion systems, and the motors that drive them. Casters are a different industry, and your best solution is probably a company that does casters every day.

Here's what I learned from a few rejected orders and a couple of awkward phone calls. A vendor who tells you "that's not what we do, and here's who does it better" is a vendor worth keeping. The one who says "sure, we can do that" without asking about your application? That's when I get nervous.

So that's the checklist. Six steps, no magic. Write the motion profile, check the bearing definitions, verify load ratings, match the motor, confirm mounting details, and demand data. Do those, and you'll skip most of the mistakes I made.

And if you need ball bearing casters? Seriously, call a caster company. We'll still be here when the linear part is ready.