Weaving interlaces lengthwise warp with crosswise weft through three repeated motions, shedding, picking and beating, and a continuous machine also needs two slow ones, letting off warp and taking up cloth. At 100 picks a minute one pick lasts 0.6 s, so the shed must stay open for at least 40-60 degrees of the crank’s turn while a shuttle crosses a 1 m warp in 0.067-0.10 s.
Part of Power Loom Construction
The repeated motions of weaving and how a power loom times them from one shaft.
Three Motions Repeat, Two Creep Forward
The Power Loom Construction overview lists the three motions every weaver repeats: shedding, where half the warp threads rise and half drop to open a V-shaped gap; picking, where a shuttle carrying weft crosses the gap; and beating, where a reed pushes the new weft against the last. The hand version is in Weaving and Heddle System. A power loom runs all three from a single power source.
A loom that weaves a long piece without a person adjusting it also needs two slow motions: warp is let off from the warp beam so the tension stays steady, and cloth is taken up on the cloth beam at a rate that sets the picks per centimetre (Warp Tensioning and Let-Off). Without them the loom stops after a few centimetres.
Each has its own page: Shedding, Picking, Beating Up.
One Revolution Is One Pick, And The Shed Has A Time Window
On the overview’s loom the crankshaft turns once per pick, at 60-120 picks a minute. Take 100: one pick lasts 60 ÷ 100 = 0.6 s. The overview gives the shuttle speed as 10-15 m/s; crossing a warp 1 m wide takes 1 ÷ 15 = 0.067 s to 1 ÷ 10 = 0.10 s. The shed must be open for at least that long. As a fraction of the pick, 0.067 ÷ 0.6 = 11% to 0.10 ÷ 0.6 = 17%, which is 11% × 360° = 40° to 17% × 360° = 60° of crank angle. The figure is a minimum for the shuttle crossing the warp alone; the shuttle also has to enter and leave the shed, so the real window is wider, and it is the first constraint on the cam shapes (Cam Shedding Mechanism). A plain-weave pattern repeats every two picks, so the cam shaft runs at half the crank speed.
The Reference Loom In This Tree
The articles in this tree use one loom so their numbers agree. The width is 1 m, the warp is the Ne 20 yarn of the spinning tree at 20 ends per cm (2,000 ends), the picks are 20 per cm, and the speed is 100 picks a minute. The sett is an assumed value that the yarn supports: for plain weave the corpus uses half the yarn’s wraps per inch as the ends per inch (Weaving); a count of Ne 20 wraps at about 125 per inch if its diameter is 0.2 mm (recalled formula, not from the corpus), so the rule allows about 62 ends per inch, 25 per cm. The overview’s 30 ends per cm (3,000 heddles) would need a yarn finer than Ne 20, about Ne 30 by the same rule.
Cloth advances 100 ÷ 20 = 5 cm a minute, 3 m an hour, 24 m in an 8-hour shift. The overview’s 20-40 m a day agrees. By hand an experienced weaver makes 1-2 m a day on a 90 cm floor loom (Weaving), so the loom replaces 24 ÷ 2 = 12 to 24 ÷ 1 = 24 weavers on that figure, near the overview’s 10-20.
What The Loom Needs From The Rest Of The Plant
A loom consumes 12 km of yarn an hour, the output of about 79 spindles (Multi-Spindle Frame Assembly), and needs 375-750 W (overview) from a drive that does not vary (Power Drive System), and a person who can repair it. It is a system, not a machine.
What You Need
- A power source and drive with a stop the weaver can reach.
- Warp yarn meeting the warp specification (Thread Quality Control).
- A frame, heddles, reed, shuttles and weft bobbins (the pages that follow).
Common Mistakes
- Counting the loom’s output without its yarn supply.
- Setting the shed window by the pick time alone, forgetting the shuttle’s flight.
- Skipping the slow motions in the plan.
Safety
Moving slay, shuttle and crank, and a drive the weaver cannot stop from the loom
The reed swings, the shuttle flies at 10-15 m/s and the crank turns while the weaver stands at the loom, and nothing about a belt or line shaft lets the weaver stop it by letting go. Know where the stop is, how long the loom coasts and who can reach the water gate (Power Drive System). Do not reach into a running shed to join a broken thread; the corpus keeps children away from running machinery (Task Assignment by Age).
What’s Next
- Learn next: Shedding — the first motion in the cycle
- Combine with: Thread Quality Control — the warp the loom depends on