The shuttle box at each end of the race catches the shuttle and brings it to rest in a short distance, ready for the picker to throw it back. To absorb 12.5-28 J over an assumed 0.10 m of checking travel it must supply an average 125-281 N and decelerate the shuttle at 500-1,125 m/s^2, about 51-115 times gravity, so it needs a yielding leather check and a box shaped so the shuttle seats square, not bounces.
Part of Power Loom Construction
Catching and checking the shuttle at the end of its flight without damaging the shuttle, the box or the warp.
The Box Is A Brake With A Short Stroke
The overview has a matching picker and box catching the shuttle on the other side. The energy to absorb is the energy of the throw: 12.5-28 J for the assumed 0.25 kg shuttle at 10-15 m/s (Picking). Stopping it over a distance d takes an average force F = E ÷ d. With an assumed checking distance of 0.10 m:
- at 10 m/s: F = 12.5 ÷ 0.10 = 125 N; deceleration a = v² ÷ 2d = 100 ÷ 0.2 = 500 m/s², which is 500 ÷ 9.81 = 51 g
- at 15 m/s: F = 28.1 ÷ 0.10 = 281 N; a = 225 ÷ 0.2 = 1,125 m/s², 115 g
Halving the distance doubles the force. The shuttle body, the metal tips and the box all take that load every pick, 48,000 times a shift: a total of 48,000 × 12.5 = 0.60 MJ to 48,000 × 28.1 = 1.35 MJ of impact energy per shift, absorbed in a few leather pads and the box wall.
Too Stiff Is As Bad As Too Soft
A hard stop returns energy: the shuttle rebounds toward the shed and may re-enter it or lie half in the box with its tail in the warp, where the next beat of the reed catches it. A box that gives too much lets the shuttle travel too far and strike the end. The check works best as a progressive brake: a leather pad on the end wall, a strap that is pulled tight as the shuttle goes in, a box long enough for the full stroke, and a wall or lid that guides the shuttle to rest square on the race. The overview’s title for this stage, box and checking, names the two parts.
The shuttle must come to rest fully inside the box, so the picker meets it squarely. A shuttle caught half out is struck off-centre, flies crooked and is likely to be trapped.
What You Need
- A box with a floor level with the race, side walls and an end wall, sized to the shuttle with a little clearance.
- Leather pads and a check strap (Leatherwork, Riveting and Lacing).
- A picker and stick at the same box.
- A rule and a straight-edge for aligning the race and boxes.
Method: Setting The Box And Check
Step 1: Align the box floor with the race, with no step in either direction.
Step 2: Fit the pad and strap and set the stopping distance so the shuttle just seats.
Step 3: Throw by hand a few times, then at low power, and watch where the shuttle stops.
Step 4: Adjust the check: a shuttle that rebounds needs a softer or longer check; one that hits the end needs a firmer one.
Step 5: Inspect each shift for cracked walls, worn pads and slack straps.
Worked Example
A stop in 0.05 m instead of 0.10 m doubles the force to 250-562 N, about 25-57 kg-force, on a shuttle of about 0.25 kg. The 0.10 m check is better for the shuttle; its cost is a longer box and more space at each end of the race. If the loom’s frame cannot house a 0.10 m check, the shuttle speed must fall, because energy scales with speed squared: dropping from 15 to 12.5 m/s drops the energy from 28.1 to 19.5 J, a 31% cut.
Common Mistakes
- Making the box exactly the shuttle’s length, leaving no room to brake.
- A hard wooden end wall.
- A race that is higher than the box floor, which makes the shuttle jump.
- Worn pads left in service.
Safety
A rebounding shuttle leaves the loom
A shuttle that rebounds or breaks the box flies out of the loom at speed. Guard the box ends, keep the line of flight clear and replace worn pads before they fail. Clear a stuck shuttle only after stopping and locking the loom (Power Drive System). Children keep away from running machinery (Task Assignment by Age).
What’s Next
- Learn next: Bobbin Winding — preparing the weft the shuttle carries
- Combine with: Fly Shuttle Design — the throw that the box receives