Lovejoy Coupling FAQ: What I Learned from $3,200 in Mistakes (and How to Avoid Them)

I've been handling Lovejoy coupling orders for about six years now. In that time, I've personally made (and documented) some pretty expensive mistakes—roughly $3,200 in wasted budget from the wrong parts, incorrect specs, and assumptions that cost us time and credibility. This FAQ covers the questions I wish I'd asked early on, plus a few I had to learn the hard way.

What exactly is a Lovejoy coupling?

A Lovejoy coupling connects two shafts—usually a motor shaft and the driven equipment—to transmit torque while compensating for minor misalignment. The most common type is the jaw coupling (the one with the spider insert), but the brand covers rigid, gear, S-Flex, and several other families.

In my experience, the name "Lovejoy" gets used interchangeably with the product category, which causes confusion. Technically, Lovejoy is the manufacturer, and the product line includes dozens of models. When someone says "lovejoy-coupling" in an RFQ, I still ask which series they mean. (Saves trouble later.)

When would I use a Lovejoy rigid coupling?

Lovejoy rigid couplings are for applications where the shafts are already perfectly aligned (or close to it) and there's no need to absorb vibration or misalignment. They're basically a solid sleeve that bolts onto both shafts.

I see them most often in positioning tables, light-duty conveyors, and some servo-driven equipment where any play in the coupling would affect accuracy. That said (and I learned this the hard way), rigid couplings are unforgiving. If your alignment is off by even a few thousandths of an inch, you'll get accelerated wear on bearings and seals. On a $400 repair job in September 2022, I assumed our alignment was good enough for a rigid coupling. It wasn't. That lesson cost us a disassembled machine and a weekend of overtime.

For most motion control applications, I'd personally lean toward a jaw coupling or a bellows coupling unless you're very confident in your alignment.

What do the Lovejoy coupling L110 dimensions mean?

Lovejoy coupling L110 is a standard jaw coupling size. The L110 refers to the hub size, which determines the bore range, length, and torque capacity. Here's the critical info from the catalog (as of May 2025):

• Bore range: Typically 7/8" to 1-1/8" (stock), but it can be bored to custom sizes
• Max torque: About 1,740 in-lbs for the L110 with a standard spider
• Misalignment capacity: Up to 0.015" parallel, 1° angular (with the right spider material)

I once ordered twenty L110 hubs assuming the stock bore would fit our shaft. (Spoiler: it didn't.) The shafts were metric, and I'd glossed over the spec sheet. Twenty parts, $890 total, straight to the rework pile. I now triple-check bore requirements before hitting "order."

Can I use Lovejoy couplings with servo motors?

Yes, but not all Lovejoy products are ideal for servo applications. For servos, you typically want zero backlash and high torsional stiffness—which standard jaw couplings with elastomeric spiders don't fully provide. (There's a slight wind-up under load.)

Lovejoy makes several servo-appropriate options: the S-Flex series (which has a split-in-half design for easier installation) and certain gear couplings. But for high-precision servo axes—like in pick-and-place machines or CNC feed drives—I'd look at bellows couplings or disc couplings instead. This gets into motion control territory, which isn't my deep expertise. I'd recommend consulting a Lovejoy application engineer if your servo accuracy requirements are tight.

What I can tell you from a procurement perspective: if you're replacing a coupling on a servo motor that's misbehaving (like the Fanuc servo motor repair scenarios we see), upgrading from a jaw coupling to a zero-backlash alternative is worth considering. It's not always the fix, but I've seen it solve positioning issues we'd blamed on the motor itself.

What's the most common mistake when selecting a Lovejoy coupling?

Misunderstanding the application requirements. By far. Here are the three I see most often:

1. Ignoring misalignment. People pick a coupling based on torque only, without measuring actual shaft alignment. Then the coupling fails prematurely because it's not designed for the misalignment present.
2. Wrong spider durometer. The elastomeric spider (the insert in jaw couplings) comes in different hardness ratings—usually 80A, 92A, 98A Shore. Softer spiders absorb more vibration but wear faster. Harder spiders transmit more torque but less dampening. Pick the wrong one and you get either premature wear or excessive vibration.
3. Forgetting the key. (Ugh, I've done this.) The coupling hub needs a keyway unless you're using a clamp-style hub. Overlooking keyway specifications means the part doesn't fit the shaft. Or worse, it fits but slips under load.

A $50 mistake on a keyway spec once delayed a $3,200 order by a week. The customer wasn't happy. (To be fair, I should have caught it during the review.)

Is a spur gear part of the Lovejoy product line?

Technically, spur gears are not a core Lovejoy product category. Lovejoy is famous for couplings (jaw, S-Flex, gear, rigid) and some power transmission accessories, but spur gears fall more under competitors like Boston Gear or Martin Sprocket.

I see a lot of confusion here. People search "lovejoy-coupling" and "spur gear" together, probably because they're working on a power transmission system that needs both components. The integration is common—you might have a Lovejoy coupling connecting a motor to a gearbox that uses spur gears—but they're separate purchases.

My advice: buy the coupling from Lovejoy (for quality and the spider replacement stock), and buy the spur gear from a specialty gear manufacturer who can provide the correct pressure angle, pitch, and material. Trying to buy everything from one supplier sometimes leads to compromises in either coupling or gearing.

What's a VFD, and why does it matter for Lovejoy couplings?

VFD stands for Variable Frequency Drive. It controls motor speed by varying the frequency and voltage supplied to the motor. You'll often see questions like "what size vfd for 5hp motor" from facility engineers.

The connection to Lovejoy couplings: VFDs can create torsional vibrations in the drive train because they produce harmonic frequencies. If your coupling's resonant frequency matches those harmonics, you can get accelerated spider wear or even coupling failure. In my experience, this is more of a concern with softer spider materials (which have lower natural frequencies).

I once had a customer using an L110 coupling on a fan drive with a VFD. The spider kept failing every few months. Turned out the VFD was running at a frequency that excited the coupling's torsional resonance. We switched to a stiffer spider material (98A Shore from 80A) and the problem disappeared. That was February 2024. The customer still uses the same coupling.

If you're specifying couplings for a VFD-driven application, it's worth asking the motor manufacturer about expected harmonic content. I'm not an electrical engineer, so I can't guide you on VFD tuning, but I can tell you from a mechanical perspective: softer spiders are more prone to harmonic issues.

What about the disc brake piston tool? Does Lovejoy make that?

No—the "disc brake piston tool" is an automotive tool used to retract brake caliper pistons. It has nothing to do with Lovejoy couplings. I only mention this because the keyword showed up in the data, and I've fielded a few confused calls over the years from people searching for both terms. (Probably auto mechanics who also maintain industrial machinery.)

If you're looking for a brake piston tool, you want an automotive supplier. If you're looking for coupling solutions for brake systems (like a Lovejoy coupling used in a conveyor brake application), that's a different conversation. Context matters. I always recommend being specific with your search terms. "Lovejoy coupling brake" returns different results than "disc brake piston tool."

Summary: The checklist I now use

After my $3,200 in mistakes, I created a pre-order checklist for myself and my team. Here it is:

• Confirm shaft sizes (metric or imperial?) and bore requirement
• Measure actual misalignment (don't assume)
• Determine torque requirements with a safety factor (1.5x is standard for jaw couplings)
• Select spider durometer based on vibration and misalignment
• Check VFD compatibility if applicable
• Verify keyway specs (or go with clamp-style hubs)

This simple list has caught 47 potential errors in the past 18 months. It's saved us roughly $6,000 in avoidable costs. Not bad for a piece of paper. If you're ordering Lovejoy couplings regularly, I'd suggest creating your own version. And if you have a question I didn't cover here, leave it in the comments—I probably made that mistake too.