Beating up pushes each new weft thread against the cloth edge with a reed carried on a swinging slay, once per revolution of the loom. At 20 ends per cm with two ends in each slot the reed needs 10 dents per cm, 1.0 mm apart, and every warp end is dragged through its dent on each of 100 beats a minute, so the reed finish and the warp surface decide how many ends break.
Part of Power Loom Construction
Packing the newly laid weft against the cloth edge with the reed, and what the beat demands of the warp.
The Reed Does Two Jobs At Once
The overview: a reed, a comb, pushes the new weft thread tightly against the previous ones. The reed also spaces the warp ends evenly, since each passes through a slot (dent). In the hand loom of Floor Loom Construction the dents per cm are 8-10 for fine fabric, with thread spacing of 1.0-1.25 mm.
For the reference loom (2,000 ends, 20 per cm; Weaving Mechanics) put two ends in each dent: dents per cm = 20 ÷ 2 = 10, a dent pitch of 1 ÷ 10 cm = 1.0 mm. At the corpus’s top figure of 10 dents per cm this is a fine reed. Two Ne 20 ends of about 0.2 mm (recalled diameter, not from the corpus) occupy 0.4 mm of that 1.0 mm, leaving 0.6 mm for the dent wire and clearance. A thicker wire leaves the ends crowded and chafing.
Picks Per Centimetre Come From Take-Up, Not From The Beat
How many weft threads per centimetre end up in the cloth depends on how far the cloth advances between picks, which is the take-up setting (Take-Up and Cloth Beam). The beat packs the pick to that position. A weak beat leaves picks that spring back and make a soft, uneven cloth; a very hard beat strains the warp at its worst moment, since warp tension rises as the reed pushes the cloth edge forward (standard weaving mechanics, recalled). Aim for a firm beat that is the same every time.
A Crank-Driven Slay Dwells At The End Of Its Stroke
If the slay is driven by a crank of radius r through a connecting rod (Crank Mechanism), its speed is roughly ω r sin θ and falls to zero at the front dead centre, where the beat is made. At 100 rpm, ω = 10.47 rad/s, and for an assumed r = 0.1 m the peak speed is 10.47 × 0.1 = 1.05 m/s mid-stroke. At the front dead centre the crank has a large mechanical advantage, so the reed arrives gently but pushes hard. The timing follows from the geometry: the reed is back at the far dead centre while the shuttle crosses, and forward at the beat.
What You Need
- A reed with dents of smooth, hard wire, bamboo or hardwood, all the same width, glued or bound into rails (Floor Loom Construction).
- A slay, a swinging frame (the sword and rails) that carries the reed and the shuttle race.
- A crank and connecting rod to drive it.
- Smooth warp (Thread Quality Control).
Method: Setting The Beat
Step 1: Choose the dents per cm from the ends per cm and ends per dent.
Step 2: Check each dent for burrs by drawing a length of the warp yarn through it.
Step 3: Set the slay stroke so the reed reaches the cloth edge at the dead centre.
Step 4: Weave a short piece and measure picks per cm over several places; look for streaks.
Step 5: Examine the warp just behind the reed for fuzz building up, which is the sign of abrasion.
Worked Example
The reed rubs each end on every beat. Over 100 m of warp at 20 picks per cm there are 200,000 beats; a yarn element that travels from the heddles to the cloth edge across 15 cm (an assumed zone) at 20 picks per cm meets the reed on 15 × 20 = 300 beats. Each element of the warp is thus rubbed 300 times in the beating zone before it is woven in, and 300 passes through a rough dent or on a fuzzy yarn is plenty to break it. Sizing the warp (Warp Beam) and a polished reed are the two defences.
Common Mistakes
- A rough or burred reed.
- Beating late, after the shed has started to close, which crushes ends.
- Letting the warp go slack, so the reed pushes the cloth edge back.
- Ends crowded three to a dent without checking the yarn diameter.
Safety
The slay swings through the weaver's reach
It carries a reed with wire or blade dents and the full weight of the beam; a hand or arm between reed and cloth edge is crushed at 100 beats a minute. Stand clear of its arc, fit a guard at the ends of its swing, and join broken threads only on a stopped, locked loom (Power Drive System). The corpus keeps children away from running machinery (Task Assignment by Age).
What’s Next
- Learn next: Loom Frame Design — the structure that carries these forces
- Combine with: Take-Up and Cloth Beam — what sets the picks per centimetre