The shuttle mechanism has three jobs repeated at the loom’s pace: throw the shuttle through the shed with a picker, catch it in a box at the far side, and keep it supplied with weft. At 100 picks a minute a 1 m loom pulls 100 m of weft a minute off the bobbin, so an assumed 25 g bobbin runs out in about 8.5 minutes and the weft supply is as much a part of the system as the throw.
Part of Power Loom Construction
How the shuttle is thrown, caught and re-supplied with weft, and how the pieces fit together.
Three Parts, One Cycle
The overview describes the shuttle mechanism as the automatic throw. Its parts are separate pages: the shuttle and its picker (Fly Shuttle Design), the box that catches it (Shuttle Box and Checking), and the weft bobbins it carries (Bobbin Winding). The cycle is the shuttle leaves a box at one side, crosses the open shed in 0.067 to 0.10 s (Weaving Mechanics), is stopped in the box on the other, and is launched back on the next pick. The energy of each throw is 12.5-28 J on the assumed 0.25 kg shuttle (Picking).
The hand-thrown ancestor is in Weaving; the overview credits John Kay’s 1733 fly shuttle with doubling weaving speed.
The Weft Runs Out Fast
Each pick lays one width of weft. On the reference loom (1 m wide, 29.5 tex weft; Weaving Mechanics) one pick uses 1 m of yarn weighing 29.5 mg. A bobbin that holds 25 g (assumed; weigh your own) therefore gives 25,000 mg ÷ 29.5 mg = 847 picks, which at 100 picks a minute lasts 8.5 minutes. In an 8-hour shift that is 480 ÷ 8.5 = 56 bobbin changes per loom. The weft consumed is 100 m a minute, 6 km an hour, as in Multi-Spindle Frame Assembly. Every change stops the loom or needs a second person, and a weft that runs out unnoticed weaves a thin place.
The winding side must therefore deliver bobbins at that pace. A loom needs a bobbin every 8.5 minutes and a winder that can wind at least 100 m of weft a minute to keep up with it.
What Goes Wrong Between Throw And Catch
- Weak pick: the shuttle stops in the shed. The reed then beats against it and breaks warp ends; a stopping device or a reed that can give way is the usual protection (historical practice, recalled).
- Rough or warped race: the shuttle rides over a bump or wedges.
- Shed closing early: the shuttle is struck by the lower layer.
- Weft tension wrong: loops form at the selvedge, or the weft pulls tight and narrows the cloth.
What You Need
- Shuttles of hardwood with metal tips (Fly Shuttle Design).
- Pickers, sticks and boxes at both sides.
- Bobbins and a winder to match the loom’s use.
- A weft stop or an attentive weaver.
Method: Bringing The System Up
Step 1: Make the shuttle and race first, and test a hand-thrown shuttle on the race.
Step 2: Fit the picker and boxes and run slowly by hand, checking that the shuttle seats fully.
Step 3: Load a bobbin, thread the shuttle eye and pull the weft to a light tension.
Step 4: Run at low speed, watching for shuttle rebound or a trapped shuttle.
Step 5: Raise speed gradually while counting weft consumption.
Worked Example
If the loom is slowed to 60 picks a minute, the same 25 g bobbin lasts 847 ÷ 60 = 14 minutes, and the shift needs 480 ÷ 14 = 34 changes. Slowing the loom by 40% cuts the changes by the same fraction; a larger bobbin gives the same effect without slowing: a 50 g bobbin doubles the interval to 17 minutes at 100 picks a minute.
Common Mistakes
- Designing the throw and forgetting the supply.
- A bobbin too big for the shuttle, which jams.
- Letting weft run out between changes.
- Raising loom speed to catch up and breaking more ends.
Safety
A trapped or thrown shuttle
The shuttle is a projectile at 10-15 m/s, and a trapped one is under the reed’s beat. Never reach for a trapped shuttle on a running or coasting loom: stop the loom at the belt, lock it, and let the slay and crank halt before a hand goes in. Know who reaches the water gate (Power Drive System). Changing a bobbin is done on a stopped loom, and children keep away from running machinery (Task Assignment by Age).
What’s Next
- Learn next: Fly Shuttle Design — the shuttle itself
- Combine with: Bobbin Winding — supplying the weft