Domestic vintage sewing machines were designed for housewives of the era. Intended to be a household tool, the machines can handle diverse materials; in the 1940s and ‘50s, the average housewife might be called upon to make everything from clothing to drapery to slipcovers for the couch. She might be sewing something as light as lace, or mending something as heavy as an overcoat. While not necessarily brilliant at any one thing, the domestic machine had to be flexible enough to cover the range.
Industrial sewing machines are intended for use in factories, where people work in assembly lines on highly specific tasks with consistent materials. Some machines are designed to sew shirt cuffs; others are designed to put the waistband on a pair of jeans; still others are designed to attach zippers. Whatever the task, the operator sits there and does that same task over and over again, and the machines are specific to the material weight and the task. An industrial machine is not versatile, but is excellent at performing a few specific tasks.
If you think about it, it’s obvious that a factory making silk bras will have different machine needs than a factory making overcoats. Both will be using industrial machines, and those machines may be completely different from each other. That's why it's pretty dumb if someone says to you, "Hey, you wanna buy an industrial machine? I have an industrial machine!" It's like someone saying "Hey, you need some medicine? I have medicine!" You have medicine, or an industrial sewing machine, that's used for what? If I'm making parachutes and your machine came from a panty factory, it does me no good. I might as well buy cholesterol pills for a broken leg.
A domestic machine is used for a few hours at a time, and during that usage, it is not running constantly. The sewist puts down a line of stitches, then pauses to adjust the material, insert or remove pins etc., then puts down another line of stitches. It is stop-and-go work and the machine is designed accordingly, with a small motor and standard-sized components.
Let's look at the underpinnings of a 15-91:
Underside of a typical domestic machine. (Oil bottle for scale.)
In contrast, industrial machines are designed for factories, and factories make money by running full-tilt. Your average factory worker puts the pedal to the metal and cranks out hundreds or thousands of pieces a day. Accordingly, industrial machines have powerful motors, thicker shafts, stronger bearings, and beefier gears. They use more steel inside than a domestic does.
Let's look at the underpinnings from a Singer 111w155:
Underside of an industrial features much thicker, heavier parts. (Oil bottle for scale.)
Whether specifically designed to sew silk or heavy leather, an industrial machine uses more robust parts than a domestic, because an industrial must stand up to the abuse of long hours of constant high-speed usage.
Note that the beefy connecting rod, at center-right, looks like something you'd find in a car.
While not the end-all be-all, the motor is the most obvious indication that you’re dealing with an industrial versus a domestic machine.
I recently bought the Singer 111w155 pictured up top, which is a true industrial, designed to produce automotive upholstery. Take a look at the motor that was connected to it:
Now look at the potted motor of the Singer 15-91, one of the machines I frequently see FALSELY advertised as “Industrial Strength:”
Let's look at them side-by-side:
Get the idea? Even if you know nothing at all about motors, do you honestly believe the one on the left is capable of doing the same thing as the motor on the right? If so, why would factory owners bother buying the bigger motors?
Most industrials have motors that are 1/2 horsepower or 3/4 horsepower. Your average domestic Singer’s motor isn’t measured in horsepower, it’s measured in amps (short for amperes), a unit of electric current.
Horsepower and amps aren’t easy to compare-it’s a bit like comparing how much money Person A has, to Person B’s earnings potential-but if we put them on a rough scale, 1 amp is equal to approximately 1/10 horsepower.
Some sellers will boast that they’ve outfitted their machines with 1.5 amp motors, which according to them, makes them “industrial strength.” Simply not true. A 1.5 amp motor is still less than 33% as powerful as the smallest industrial motor. So don’t be wowed by impressive-sounding numbers. Plus, as you saw above in the photos of the underpinnings, a more powerful motor alone is not enough to make a machine "industrial."
A Word About Leather
Sellers trying to inflate the capabilities of their machine love to put “Sews leather!” in their description. This is a ridiculous and value-less statement, because leather comes in many different thicknesses and types. The lightest, cheapest garment-weight leather is easy to put stitches in on ANY machine, including those plastic Wal-Mart junk jobs. Bring me the crappiest sewing machine you have and I’ll show you a lightweight piece of leather I can sew on it.
What these sellers are hoping is that you’ll believe that if you buy one of their machines, you’ll be able to make gun holsters and horse saddles with their “Industrial Strength” model 99s. Which is, of course, ridiculous.
Some sellers will go a step further and show photos of their machine sewing through thick leather belts. Folks, I have no doubt you can coax a domestic into temporarily sewing through thick leather. I also don’t doubt you could take the Toyota we saw earlier, tie that trailer to the back of it, and under the right conditions, get it to move. But how far do you think you’ll get? And how well do you think that Toyota’s going to hold up before it breaks down?
Here’s the bottom line: The guy bragging about his machine’s leather capabilities is trying to sell it to you. Wouldn’t you rather learn about leather machines from someone who sews leather for a living and isn’t trying to sell you anything?
If so, the forums over at Leatherworker.net are a great place to start. There’s a section called “Leather Sewing Machines” where people with decades of leather experience discuss different sewing machines appropriate for those tasks. Needless to say, you won’t find anyone raving about “Heavy Duty” model 66s.
A Word About “Heavy Duty”
Apart from the sellers who’ll actively lie to you about their machines’ capability, there are others who misinform you because they just don’t know any better. They find a sewing machine in their grandmother’s attic and figure it’s worth big bucks. They try lifting it and discover it weighs 30 pounds. They figure it’s a “heavy duty” machine because of its heft.
Folks, a domestic vintage Singer is only “heavy duty” in the sense that EVERYTHING from that era was “heavy duty”-meaning “overbuilt.” Today we have fancy software that analyzes machinery parts for manufacturers, to help them calculate the absolute thinnest and cheapest a part can be to get through 10, 000 cycles before it breaks. Back then we had no such thing. So we overbuilt everything from sewing machines to refrigerators to cars. Pull the door shut on a ’54 Buick, then pull the door shut on an ’88 Buick and see if you notice anything different.