Mechanics of sewing machines

From: veritasium

Sewing machines are ubiquitous, creating virtually every piece of clothing worn today [00:00:35]. Unlike hand sewing, where a needle is passed completely through fabric and re-grasped on the other side [00:00:16], sewing machines operate without the needle ever fully leaving the fabric [00:00:13]. This required a completely new method of sewing to be invented to allow for mechanization [00:00:27], a significant innovation in sewing technology that enabled these machines to perform “tiny mechanical miracles” every second [00:00:48].

The Challenge of Mechanizing Sewing

The primary obstacle to mechanizing hand sewing, such as a running stitch, was the need to release the needle on one side of the fabric and pick it up again on the other [00:01:40]. This action was almost impossible for early machines to replicate [00:01:52]. Thus, the history of sewing machines is marked by three fundamental breakthroughs [00:02:01].

Breakthroughs in Sewing Machine Design

1. The Eye-Pointed Needle

For tens of thousands of years, needles remained largely unchanged, featuring a sharp end and an eye on the opposite end for the thread [00:02:42]. In 1755, Charles Frederick Wiesenthal, a German inventor in England, patented a needle that was sharp on both sides [00:03:08]. This allowed the needle to pass back and forth through fabric without being flipped [00:03:23]. An unexpected benefit of this design was moving the eye of the needle next to the sharp tip [00:03:39]. This eye-pointed needle is used in all sewing machines to this day [00:03:42].

2. Securing the Thread: Chain Stitch vs. Lock Stitch

The core problem remained: how to prevent the thread from pulling out once the needle retracts [00:03:49]. The solution involved finding ways to tangle the thread underneath the fabric [00:04:00].

The Chain Stitch

The chain stitch is formed by keeping a loop of thread underneath the fabric as the needle pulls out [00:04:12]. The needle then passes through this loop, forming a link [00:04:19]. Repeating this action creates a chain of stitches [00:04:26]. This was one of the first stitches successfully performed by machines [00:04:36].

• Early Inventors:

  • Thomas Saint (1790) drew detailed patent drawings for a sewing machine, though no prototype was built [00:04:52].
  • Joseph Madersperger (1814) received a patent in Vienna but never commercialized his machine [00:05:00].
  • Barthélemy Thimonnier (1830) built a version using a barb needle to create a chain stitch and set up a factory with 80 machines, but it was destroyed by angry tailors [00:05:12].

• Reliable Chain Stitch Mechanisms (1857):

  • Charles Raymond’s Hook Design: As the needle punctures and withdraws, it creates a bulge of thread. A sharp hook catches this bulge, forming a loop, and the needle passes through it on its next descent [00:06:03].
  • James Gibbs’s Rotating Hook Design: Similar to Raymond’s, but the hook rotates, grabbing the thread and releasing the previous loop as it spins [00:06:45]. Gibbs developed 37 prototypes to perfect the looper shape [00:06:59].

• Flaw of the Simple Chain Stitch: If the thread comes loose, the entire stitching can easily unravel due to minimal friction between stitches [00:07:25]. More complex, robust chain stitches were developed, commonly found in jean hems [00:07:49].

The Lock Stitch

The lock stitch uses two separate spools of thread: a top thread from the needle and a bottom thread from a “bobbin” [00:08:30]. The needle pushes the top thread through the fabric, and the bottom spool of thread passes completely through a loop in the top thread, interlocking the two [00:08:47].

• Elias Howe patented the lock stitch in 1846 [00:09:21]. His early machine used a curved needle and could only stitch in a straight line [00:09:34].

• Allen B. Wilson dramatically improved the lock stitch sewing machine, receiving patents in 1850 and 1851 [00:09:41].

• Lock Stitch Mechanisms:

  • Vibrating Shuttle (1850 patent): An oscillating shuttle containing a bobbin moves back and forth. As the needle goes down and comes up, it forms a loop with the top thread. The shuttle passes through this loop, intertwining the top thread with the bobbin thread to create the lock stitch [00:09:51]. The shuttle’s movement is synchronized with the needle [00:10:16]. Singer Model 27, of which millions were made, used this robust design [00:10:34].
  • Rotating Hook (1851 patent): In this design, the bobbin is inside a rotating hook. The needle descends, pulls the top thread, then rises slightly to create a bulge. The rotating hook grabs this bulge, pulling more thread to pass entirely around the bobbin, forming the lock stitch [00:10:53]. This is the basis for most modern sewing machines [00:10:56].

• Tension and Needle Groove:

  • For a strong lock stitch, the tension on both the top and bottom threads must be identical so the stitch meets perfectly in the middle of the fabric [00:12:12].
  • A groove was developed in the sewing needle to reduce friction between the thread and the fabric as the thread is pulled down and up multiple times per stitch [00:12:40]. This results in less fraying and a cleaner stitch [00:12:52], and is present on practically all modern sewing machine needles [00:12:57].

3. Fabric Feeding Mechanism: Feed Dogs

Early sewing machines required manual fabric repositioning after each stitch, leading to slow and inconsistently spaced stitches [00:13:10]. Allen B. Wilson again provided the most successful solution: “feed dogs” [00:13:21].

• Mechanism: When the needle is not in the fabric, a small metal piece with grooves (the feed dogs) pushes up from below, grabs the fabric, and moves it a fraction of an inch to position it for the next stitch [00:13:25]. This design is used in virtually all modern sewing machines [00:13:41].
• Variations: Some specialized machines, like those for chain stitch embroidery, use a “universal feed” where a handle underneath rotates the machine’s “nose” and presser foot, allowing fabric to be advanced in 360 degrees [00:13:47].

Commercialization and Impact

The history of sewing machines was significantly shaped by Isaac Singer. While he did not invent the sewing machine, he was a shrewd businessman who bought patents for various parts [00:15:01]. Inspired by interchangeable parts in firearms production, he optimized the manufacturing process, dropping the price of machines from $100toabout$10 (around $300 in 2023) [00:15:14]. Singer’s company was also one of the first to offer installment payment plans, making machines accessible to families [00:15:34]. This led Singer to become one of the world’s largest corporations and the first American multinational company [00:15:44].

The impact of sewing machines on clothing production was profound:

• Before machines, sewing a single shirt took over 12 hours; it now takes less than 30 minutes [00:15:53].
• In 1900, American families spent about 15% of their income on clothing; by 2003, it was less than 4% [00:16:01].
• Despite spending less, people own more clothes, with the worldwide average number of garments owned exceeding 130 in 2019 [00:16:10].
• Annually, 100 billion garments are produced globally [00:16:19].

Despite these changes in consumption habits, the sewing machine itself is a brilliant invention, iterated and improved by dozens of people, truly revolutionizing the world [00:16:42].