Your mission: to go shopping for a sewing machine without being bowled over by the buzzwords and hype. What do all those strange words mean anyway?
This glossary is focused mostly on terms associated with older all-mechanical sewing machines, but does include some modern features. Bold terms are terms that you're likely to hear salespeople use. Non-bold terms are defined to help you understand what the buzzwords really mean.
Automatic Tension: See Tension, Automatic
Bobbin: A small spool that you wind thread onto yourself; the bobbin thread makes up the lower side of the stitch.
Bobbin Case: a device that holds the bobbin inside the shuttle, it also incorporates a tension spring that regulates bobbin thread tension.
Bobbin, Drop-in: A fixed bobbin case permanently mounted inside the shuttle set horizontally (flat) so the bobbin can just be inserted from the top surface of the workspace instead of having to first be mounted in a bobbin case and then installed.
Bobbin, Oscillating: See Shuttle, Oscillating
Bobbin, Rotary: See Shuttle, Rotary
Bobbin, Self-winding: A system where the bobbin is not removed and put on a bobbin winder to load, but instead loads while in the bobbin case (also referred to as in-place bobbin winding).
Cam: An irregular wheel with one or two bands of indentations. A 1-band cam controls the left-right movement of the sewing machine needle, a 2-band cam also controls the movement of fabric forwards and backwards under the presser foot. This allows an all-mechanical sewing machine to sew multi-step and decorative stitches.
Cam, Interchangable: A cam that can be removed from the sewing machine and replaced with another, allowing more multi-step and decorative stitches. Sometimes called a stitch wheel or fashion disc.
Cam Stack: A group of cams made as a single unit, permanently installed inside a sewing machine. An all-mechanical machine that does multiple stitches by just switching levers or dials has an internal cam stack.
Commercial: see Industrial. Often misused by eBay sellers.
Cylinder bed: the industrial equivalent to the free arm
Darning Plate: a plate that covers the feed dogs preventing them from moving the fabric forwards or backwards. Some machines don't need a darning plate because they feature fully retractable feed dogs.
Drop-in Bobbin: see Bobbin, Drop-in
Dual Feed: see Feed, Dual
Electronic Speed Control: See Speed Control, Electronic
Fashion Disc: See Cam, Interchangeable
Feed Dogs: Small toothed rails that move the fabric forwards or backwards under the presser foot while you're stitching.
Feed, Drop: The most common household sewing machine feed mechanism where, while the needle is up, feed dogs rise up, press against the fabric, and move it a short distance before dropping and moving back to their original position
Feed, Dual: An enhancement to drop feed where a moving upper foot (separate from the presser foot) clamps the fabric against the feed dogs and moves in sync with them to move the fabric. Its effect is similar to a walking foot. Most common on industrial machines and new home machines manufactured by Pfaff.
Feed, Needle: A feed mechanism only found on industrial machines, needle feed moves the fabric while the needle is in it. Unlike all other feed mechanisms, the needle is moved forwards or backwards in sync with the feed dogs as part of the feed process.
Free Arm: A fully-enclosed arm that holds the bobbin, shuttle and feed dogs, allowing you to easily pass curved fabric or loops of fabric back under the arm. Most sewing machines that feature a free arm also have a work table accessory that wraps the free arm to make a large flat workspace.
Industrial: A sewing machine made for the garment or other sewing trade, an industrial sewing head is very large compared to a home sewing machine. An industrial head is always mounted to a table and is driven by a 3/8" belt drive connected to large (usually 220v) external motor with a friction clutch. Specialty heads include post-bed, cylinder bed, needle-feed and automated bar-tackers. The term (and related terms such as commercial) are often misused by eBay sellers.
In-place Bobbin Winding: See Bobbin, Self-Winding
Interchangeable Cams: see Cam, Interchangeable
Lock Stitch: The stitch every modern sewing machine does. The needle passes a loop of thread through the fabric being sewn. A shuttle catches the loop and passes it around the bobbin, wrapping the two threads together. Finally, the needle pulls the loop and caught thread back up through the fabric, leaving the loop in the thickness of the fabric and showing an even line of stitching on each side.
Needle Control: A feature often associated with Electronic Speed Control, Needle Control stops the motor with the needle either in the "up" or "down" position only, and allows you to use the Speed Controller to advance the machine 1/2 stitch at a time. This is clever, but can be done as easily by moving the hand wheel manually.
Needle Feed: see Feed, Needle
Needle Plate: The slick plate that the presser foot holds the fabric against. The needle plate has a hole in it that the needle passes through to carry the needle thread to the shuttle. It also has slots that the feed dogs pass through to move the fabric.
Oscillating Bobbin: See Shuttle, Oscillating
Plastic: Usually used in the phrase "No plastic gears" or "No plastic parts." Any plastic that's not Nylon. According to sewing machine marketing people, Nylon isn't plastic. Machines that say "No plastic" on the box usually have nylon gears or cams.
Presser Foot: The slick metal (or sometimes plastic) foot that holds the fabric down for stitching. Often, lifting the presser foot releases the needle thread tension.
Rotary Bobbin: See Shuttle, Rotary
Self-Winding Bobbin: See Bobbin, Self-Winding
Shuttle: A circular hook that moves around the bobbin case, looping the needle and bobbin threads together to form a stitch.
Shuttle, Oscillating: A shuttle where the hook rotates forward in a partial circle, catches the needle thread and then rotates back to its original position, releasing the needle thread and completing the stitch.
Shuttle, Rotary: A shuttle where the hook rotates forward, catches the needle thread and continues to rotate forward, releasing the needle thread and completing the stitch before continuing on to its original position. This continuous rotation maintains more consistent thread tension while a stitch is formed than the back-and-forth movement of an oscillating shuttle.
Speed Controller: A foot pedal or knee bar that controls the speed at which the sewing machine motor runs.
Speed Control, Electronic: A speed controller that uses an electronic circuit rather than a simple rheostat to control the speed at which the sewing machine motor runs. Where a rheostat-based speed control delivers less motor power at lower speeds, an electronic speed control delivers full motor power at all speeds.
Stitch Wheel: See Cam, Interchangeable
Tension: The drag (friction) applied to the needle thread and bobbin thread as the thread is used. Bobbin tension is usually pre-set and needle thread tension is adjustable. If needle thread tension is too high, the bobbin thread will be pulled to the upper side of the fabric; if it's too low the needle thread will be pulled to the lower side of the fabric. When the needle thread tension is just right, the threads will lock together without showing loops on either side of the fabric.
Tension, Automatic: While thread tension does need to be adjusted to account for different fabrics and threads, most sewing can be done without much tension adjustment. Marketers labeled this pre-set tension level as "Automatic Tension." A machine that lets you adjust away from this preset level is great, as sometimes it's necessary. A machine that only has "Automatic Tension" is often a disaster when you try to sew with threads or fabrics not appropriate to its setting.
Throat Plate: See Needle Plate
Walking Foot: A presser foot mounted on springs; when the needle is in the "up" position the foot can slide forwards or backwards as the feed dogs move, reducing friction on the upper piece of fabric. An industrial machine's "walking foot" is entirely different, and usually refers to dual feed