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Many vintage sewing machine ads tout the wonders of a "powerful 1.0 amp motor," which sounds impressive.
But the Singer 401 has only a a .72 amp motor. Does that mean it's less powerful than the 1.0 amp machine?
What is an amp? How many do I need? Does it even matter?
An amp (short for ampere) is a measurement of electrical current. The amperage of an electric motor is the amount of electrical current required to run the motor. If a motor draws more current it usually produces more power.
Is "more power" always a good thing? Not necessarily. If you ever watched the sitcom "Home Improvement" you've seen what happens when an oversized motor is attached to a home appliance. (Remember the dishwasher?) Not good.
Those episodes were exaggerated for comic effect, but the principle holds true. An electric motor needs to be the right size and right power for the task at hand. Under-amped or over-amped are equally undesirable.
Let's compare the .72 amp motor from a 401 with a 1.0 amp motor from a belt-driven Class 15 "Singer Clone":
The .72 amp motor has a long motor shaft because the motor sits inside the machine and the gear at the end of the motor shaft directly engages the needle-bar and hook mechanism inside the machine. There are no belts.
The 1.0 amp motor has a short shaft with a pulley that connects to the machine via a belt on the handwheel. The handwheel turns the needle-bar and hook mechanism inside the machine. A belt-driven sewing machine typically needs a more powerful motor because power is lost in the transfer from motor to mechanism (via the belt). A higher amp motor compensates for this loss of power. (Note: additional power will be lost if the belt is too tight or loose.)
So when you are shopping for a vintage machine, it's not just the size of the motor that counts, it's the design of the machine that determines how much power is needed to drive the mechanism.
Which means that a .72 amp motor packs the appropriate punch for the Slant-o-Matic family, but a 1.0 amp motor provides the added "oomph" that a belt-driven machine needs.
Whichever machine you choose, make sure the size of the motor is appropriate. It's possible to attach a bigger motor to belt-driven machines, but "more power" can place undue stress on the machinery, which may shorten the machine's life. You need enough power, but not too much power.