Two-thread lockstitch machine.
How do two threads become a lockstitch?
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How do two threads become a lockstitch?
Fit all six essential stitch assemblies.
As the needle rises it leaves a loop behind its scarf. The rotating hook carries that upper-thread loop around the stationary bobbin, enclosing the lower thread. The take-up pulls the crossing into the fabric. A feed dog advances the cloth only after the needle withdraws; relative tension decides where the interlock rests.
Schematic two-thread 301 rotary-hook machine, not an identified production model. A 15 mm crank and 45 mm rod give 30 mm needle stroke; the hook turns twice per mainshaft revolution. JUKI LU2 examples use 2.4 mm needle rise for pickup and 1 mm maximum feed height. This lesson uses an explicit 2.0–2.8 mm pickup teaching band, not a factory tolerance, and an illustrative 0.8–1.2 balanced tension band. Knot location shows only the qualitative effect of relative tension. Slow-motion cycles/s are not machine rated speed. Thin red/blue paths explain thread topology; they are not metal solids. Continuous motion demonstrates the cycle; only requested full-cycle hand tests accumulate stitch count and sewn length. A fixed section window reveals advancing cloth surface marks; a raised two-layer swatch exposes the interlock. Friction, elasticity, motor load, thread stretch and bobbin depletion are not simulated.
Hand-test four balanced stitches of 2–4 mm. Set hook pickup to 2.0–2.8 mm needle rise and upper/bobbin tension ratio to 0.8–1.2.
Follow two threads through one lockstitch.