Lovejoy Couplings: 6 FAQs from a Procurement Manager's Desk

Why I stopped treating all Lovejoy couplings as interchangeable

When I first took over purchasing in 2020, I figured a 'Lovejoy coupling' was a Lovejoy coupling. Just pick the size, order, done. Took about three orders — and one costly mismatch — to learn that spider for Lovejoy coupling isn't always the same as a standard jaw spider. So here's what I wish someone had told me upfront.

1. What's the difference between L-type, S-Flex, and Gear Lovejoy couplings?

Honestly, I used to think they were just different colors. Then a maintenance guy pulled me aside after I ordered L-sizes for a high-torque servo application. Basically: Jaw (L-type) is your everyday workhorse — good for general shaft alignment, moderate torque. S-Flex is the cushioned version — it handles more misalignment and dampens vibration. Gear is for heavy-duty, high-torque stuff where you need metal-on-metal strength. I learned this the hard way when a gear coupling spec I ignored caused a motor coupling failure. Now I always match the coupling type to the motor's torque curve.

2. Can I use any spider for Lovejoy coupling?

No — and I tried. Thought a generic urethane spider would save $12. The result: it disintegrated in three months. Lovejoy spiders (the rubber insert) come in different durometers: standard (NBR), Hytrel, and urethane for specific temp ranges and chemical resistance. The catalog lists which spider fits which coupling size. For example, the L095 uses a size 5 spider. If you grab a size 6 — well, my supplier had to overnight the right one. So check the part number. And if the application runs hot (like near a motor), use Hytrel. That's one of those "didn't know until it failed" lessons.

3. How do I match a Lovejoy shaft coupling to a Kollmorgen servo motor?

Kollmorgen servo motors — especially the AKM series — have specific shaft diameters and keyways. When we were replacing a worn coupling on a Kollmorgen servo motor, I initially ordered a standard jaw coupling with a straight bore. Problem: the motor shaft was metric with a flat. We needed a coupling with a metric bore and set screws — or a clamp-style coupling. Lovejoy's SD series (clamp-style) worked perfectly. Bottom line: always get the motor's shaft drawing before ordering. I now keep a spreadsheet with shaft dimensions for our 3 most common servo brands (Kollmorgen, Fanuc, Siemens). Saves me a week of back-and-forth.

4. What does a VFD actually do — and do I need one for my Lovejoy coupling setup?

I was embarrassed to ask this early on, so I'll be direct. A VFD (variable frequency drive) controls motor speed by adjusting frequency and voltage. It's not a coupling thing — it's a motor control thing. But if you run a motor through a VFD at very low speeds, the torque characteristics change. That can affect coupling selection. For example, at 5 Hz, some motors deliver less starting torque; a soft-start coupling like S-Flex might slip less than a stiff jaw coupling. We had a conveyor that used a 5 Hp motor with a VFD — the original Lovejoy L110 coupling broke under low-speed torque spikes. Switching to a jaw coupling with a higher torque rating solved it. So while VFD doesn't directly dictate coupling type, it's part of the system equation.

5. What conveyor chain types work with Lovejoy couplings?

I'm not a conveyor engineer — I just buy the parts. But I've learned that conveyor chain types (roller chain, engineering class, or specialty) affect the shaft loading. A Lovejoy coupling at the motor-to-gearbox connection sees different stresses if the conveyor chain is heavily tensioned or has jerky starts. For a roller chain conveyor moving 200 lb boxes, a standard jaw coupling with spider might be fine. For an inclined conveyor with heavy loads, we spec a steel gear coupling. My rule: if the conveyor has a start/stop cycle every 30 seconds, oversize the coupling by one model. I'm not sure why exactly — my best guess is the dynamic loading. But it works.

6. Where can I find reliable Lovejoy coupling dimensions?

Lovejoy publishes a catalog (latest I've seen is 2024 edition) with dimension tables for every coupling type. I keep a PDF on my desktop. For quick checks, lovejoy-coupling official site has a product search tool. But honestly, the fastest way is to call an authorized distributor — they often have a coupler selector tool. I once wasted three hours cross-referencing dimensions from a third-party site that had outdated L110 specs. Now I go to the source. Also, note that bore sizes vary by stock: standard bores are inch, metric available on request. Verify before ordering.

That's the stuff I wish I had known when I started. If you're in procurement, you'll make your own mistakes — but hopefully fewer than I did.