A fly shuttle is a boat-shaped hardwood body 250-350 mm long, 40-50 mm wide and 30 mm tall, with metal tips and a hollow centre holding the weft bobbin, thrown by a leather picker on a spring-loaded or stick-driven arm. To reach 10-15 m/s over an assumed 0.15 m stroke it must be accelerated in only 0.020-0.030 s, which is 12-18 degrees of the crank’s turn at 100 picks a minute, so the launch needs a sharp blow or a stored spring, not a gentle cam.
Part of Power Loom Construction
Designing the shuttle and the picker that throws it, and the timing of the throw.
The Shuttle
The overview: the shuttle is made of hardwood (boxwood, persimmon or dogwood) shaped like a boat, with pointed metal tips for smooth travel, a hollow centre that holds a bobbin of weft, and a small hole in the side through which the thread exits. Dimensions: 250-350 mm long, 40-50 mm wide, 30 mm tall. It rides on the shuttle race, a smooth, flat, polished track in front of the reed.
Mass matters because the launch energy is proportional to it, and the overview gives none. Estimate on a rough basis: a boat shape fills perhaps 60% of its bounding box (an assumption), so 300 × 45 × 30 mm × 0.6 = 243 cm³, about half hollowed away leaves 120 cm³ of wood; at an assumed wood density near 0.9 g/cm³ (recalled) that is about 110 g, and with tips and a loaded bobbin the assumed 0.25 kg used in Picking is plausible. Weigh yours. A shuttle half as heavy takes half the energy at the same speed.
The underside must be polished flat. The shuttle slides over the lower layer of the shed; a rough or fuzzy warp snags it, and the shuttle’s own roughness fuzzes the warp. A sized warp (Warp Beam) helps both.
The Throw Must Be Fast
To leave the picker at 10 m/s and 15 m/s over a stroke d of 0.15 m (assumed) from rest at constant acceleration, the time is t = 2d ÷ v = 0.30 ÷ 10 = 0.030 s and 0.30 ÷ 15 = 0.020 s. A pick lasts 0.6 s at 100 picks a minute, so the launch occupies 0.030 ÷ 0.6 × 360° = 18° and 0.020 ÷ 0.6 × 360° = 12° of crank turn. The average force is m a, with a = v ÷ t = 333 and 750 m/s², about 83 and 188 N on 0.25 kg. A cam shaped for gentle motion cannot do this. The overview names two ways:
- A picker stick driven by a cam or tappet: a steep nose strikes the stick, which swings and carries the picker through the stroke; the strike is a shock to cam, stick and frame.
- A spring: a cam compresses a spring over a longer part of the cycle and releases it suddenly, which spreads the cam’s load over time and delivers the energy at the end. The spring must store at least the throw energy of 12.5-28 J.
The spring option is also the more controllable: the speed follows the spring tension, so it can be adjusted.
What You Need
- Dense, fine-grained hardwood that polishes (Hardwood Types).
- Metal tips, forged and fitted (Iron Applications).
- A hollow for the bobbin, a side exit hole and a means of tensioning the weft.
- Picker, strap and stick of tough leather and hardwood (Leatherwork).
Method: Making And Tuning A Shuttle
Step 1: Shape the body, hollow it, and check the bobbin seats without wobble.
Step 2: Fit the tips firmly; a loose tip leaves in flight.
Step 3: Polish the bottom and sides and test on the race.
Step 4: Weigh the loaded shuttle and compute the energy at the intended speed.
Step 5: Tune the picker: raise the spring tension or stick stroke until the shuttle arrives in the box at the target speed, measured by timing the flight over the 1 m width.
Step 6: Inspect daily for cracks, loose tips and a worn eye.
Worked Example
A flight time of 0.08 s over the 1 m width means 12.5 m/s. At 0.25 kg that is 0.5 × 0.25 × 12.5² = 19.5 J. If the spring has a stiffness of k and is compressed x, E = ½ k x². For x = 0.05 m, k = 2 × 19.5 ÷ 0.05² = 15,600 N/m, a stiff spring; at a compression of 0.10 m it is 3,900 N/m. The numbers show why leather straps and stout wooden or steel springs both appear in the historical designs.
Common Mistakes
- A shuttle heavier than needed, so every pick costs more energy and risk.
- Loose tips or cracked body.
- Overspeed to gain a few picks a minute.
- Rough race or underside.
Safety
The shuttle is a projectile launched on a stored-energy blow
A cracked shuttle breaks apart in flight; a trapped one is struck by the reed. Guard the front and ends of the race, keep out of the line of flight and the spring’s release path, and release spring tension before servicing. Stop and lock the loom first (Power Drive System). Children keep away from running looms (Task Assignment by Age).
What’s Next
- Learn next: Shuttle Box and Checking — stopping the shuttle after the throw
- Combine with: Bobbin Winding — the weft the shuttle carries