Who This Checklist Is For
I'm a procurement manager at a 200-person custom machinery company. For the past seven years, I've managed our motion control component budget—roughly $300,000 a year in ball screws, servo motors, linear guides, bearings, and conveyor modules. I've negotiated with 15+ vendors and documented every order in our ERP system. This is the checklist I actually use when I'm about to buy or re-source automation parts.
If you're the person responsible for purchasing motion control components, this article is for you. It's not a backgrounder on industrial automation. It's a practical set of checks that pulls in the details that usually get missed until something breaks.
There are five steps. The order matters because the first two steps are the ones that save the most money.
The Procurement Checklist
Step 1: Define the Operating Context, Not Just the Part Number
When a machine goes down, the fastest reaction is to order the same part number from the usual supplier. I've learned to stop before doing that. A part number only tells you what the component is; it doesn't tell you how it's loaded, how hot it gets, or how much misalignment it has to tolerate.
Take Dodge pillow block bearings. They're common in conveyor lines and bulk handling equipment. According to Regal Rexnord's engineering manuals, proper life depends on correct mounting, shaft tolerance, and real-world lubrication. Even the ISO 281 rating life standard for rolling bearings assumes clean lubrication, correct mounting, and reasonable alignment. If those conditions aren't met, the catalog life is meaningless.
The same idea applies to servo motors. When you're comparing options from any servo motor manufacturer, don't just compare peak torque and rated speed. Ask about rotor inertia, thermal limits, and feedback resolution. A motor that looks fine in a datasheet can run hot in your machine, and heat is what kills the winding insulation.
Step 2: Calculate Total Cost of Ownership, Not First Price
Here's something vendors won't tell you: the first quote is rarely the final cost. The lowest quote often becomes the most expensive order once you add internal engineering time, freight, rush charges, and the cost of unplanned downtime.
I compare quotes using a simple TCO spreadsheet. Columns: unit price, freight, lead time, MOQ, payment terms, warranty, expected service life, and engineering time. I also put a row for "risk"—if this part fails early, what does it cost us?
One example: in Q2 2024, we re-quoted servo drives for a packaging line. One regional distributor was 18% cheaper on the drive itself. The larger automation supplier included free drafting support and a temporary spare drive while our old unit was being repaired. When I added up the engineering hours and potential downtime, the cheaper drive would have cost us about $1,900 more. The "cheap" drive wasn't cheap.
Bosch Rexroth often comes up in this kind of analysis. They aren't the lowest-price supplier in most motion control categories. But if you're already using their controls, the integration cost can be lower. That's not a sales pitch; it's an input to the spreadsheet.
Step 3: Verify Automation Platform Compatibility
It's easy to assume that any Ethernet/IP or PROFINET device will plug into your existing control system and simply work. That assumption is how projects eat up their engineering budget.
Here's a concrete example. Bosch Rexroth ctrlX AUTOMATION is described in their public product documentation as an open, app-based automation platform. The company also sells the Bosch Rexroth TS conveyor range, a modular conveyor system for factory automation. You can buy TS conveyor sections and a ctrlX controller separately, but you still need to confirm how they will communicate in your specific environment. Does the controller replace the PLC you already run? Does the conveyor's motor drive accept a standard VFD, or does it need a specific Rexroth drive? What about safety I/O?
Every module you add to a motion control system adds a compatibility interface. If a vendor says "backward compatible," ask them to prove it in writing. A verbal promise doesn't help when your electrician is standing in front of a machine that won't start.
Step 4: Ask About Lifecycle and Obsolescence—Then Read the Fine Print
Factory automation equipment isn't a consumer gadget. A production line can run for 15 years, and you need spare parts, documentation, and support to match that timeline. That's why I ask every potential supplier these questions before ordering:
- How long will this product family be available?
- What is your product change notification lead time?
- If a part is discontinued, is there a migration path?
- Can you commit to spare parts availability for X years after the last order?
I learned this lesson the hard way. In 2022, we bought a batch of low-cost sensors from an online supplier. Eighteen months later, the product line disappeared. We paid a rush premium for replacements and spent 15 hours redesigning the panel. The cheap sensor saved us $240 and ended up costing us over $4,000.
Having a big name doesn't automatically make a supplier trustworthy, but it often means there is a formal lifecycle policy to review. You can ask Bosch Rexroth, or any major automation vendor, for a written statement about spares availability. If the supplier hesitates, that's useful information.
Step 5: Plan for the Moment a Component Fails
At some point, every component fails. The real question is how prepared you are when it happens. If you've ever asked, "What happens if a ball bearing goes out?" you know that the answer can be expensive.
A failing ball bearing can overheat, seize, score the shaft, and damage the housing. In a conveyor system, that can mean a production stoppage and a pile of scrapped product. But here's the part that surprises people: bearing failures are rarely caused by the bearing itself. They're usually caused by misalignment, poor lubrication, contamination, or excessive preload. The bearing is the victim, not the criminal.
So when you're buying replacement bearings—whether it's a Dodge pillow block or a precision ball screw support bearing—build a maintenance plan at the same time. Who will monitor vibration and temperature? How often? What action do you take if the reading is abnormal? If you don't answer those questions, you're waiting for a failure instead of preventing one.
And when a bearing does fail, don't just replace it. Write down the failure mode, the lubricant condition, and any unusual noise or vibration before you disassemble the housing. That record is what lets you choose a better part next time.
Honestly, I'm not sure why bearing failure forecasting is so often ignored. My best guess is that maintenance schedules get pushed aside when production pressure is high. But the extra 10 minutes of inspection typically costs less than one emergency parts order.
Common Mistakes I've Seen
I've spent over seven years tracking purchase orders and failure data. The same mistakes show up no matter which supplier is involved.
- Choosing by unit price alone. A $30 bearing that fails in three months costs more than a $60 bearing that lasts three years. That's not a slogan; it's arithmetic.
- Forgetting about lead time. Saving 5% on a servo motor doesn't help if the lead time is six weeks and your line is down.
- Over-specifying components. Buying a heavy-duty option when a standard part will do is just as wasteful as buying too cheap.
- Not keeping records of failures. Every part that fails has a story. If you don't document it, you'll probably repeat the same purchasing error.
The goal isn't to find the cheapest part. It's to avoid the most expensive part—the one that fails, takes down a line, and creates a problem that's way bigger than the price difference.
Final Thought
I'm not going to pretend this checklist is a magic formula. It's a way to force yourself and your suppliers to be specific. Before you send an RFQ for ball screws, servo motors, linear guides, or conveyor modules, send them this checklist and ask for a written response to each point. The suppliers who answer clearly are usually the ones worth paying for.
Some of my colleagues still think I overthink procurement. Maybe they're right. But in the last seven years, our component-related downtime has dropped noticeably, and the hours we spent on these checks have paid for themselves many times over. I'll take that trade any day.