A loom frame must hold the beams square and parallel while the swinging slay shakes it once per pick: an assumed 20 kg slay moving 0.1 m either side of centre pushes the frame with 219 N at 100 picks a minute and 316 N at 120. Build it from braced hardwood or cast iron, anchor or weigh it so that force cannot walk it across the floor, and square it to within a few millimetres, since the corpus warns that 5 mm of misalignment makes uneven cloth.
Part of Power Loom Construction
The structural requirements of a power loom frame and the forces that set them.
The Slay Is The Source Of The Shaking
The overview asks for a rigid frame in which any flex wastes energy and makes uneven cloth, which is square and level so that tension is even, and heavy enough not to walk when running. The main source of shaking is the slay with its reed, which moves back and forth once per pick (see Beating Up). A body of mass m moving through a crank radius r at angular speed ω exerts a force of m × r × ω² (standard mechanics, recalled). With assumed values, a slay assembly of 20 kg and r = 0.1 m:
| Picks a minute | ω (rad/s) | ω² | Force m r ω² |
|---|---|---|---|
| 60 | 6.28 | 39.5 | 79 N |
| 100 | 10.47 | 109.6 | 219 N |
| 120 | 12.57 | 157.9 | 316 N |
The force reverses direction every half turn, so it is a push-pull at 1.0-2.0 times a second. To keep a frame from creeping, its weight times the friction coefficient must exceed it. With an assumed friction coefficient of 0.5 on a timber floor, W ≥ F ÷ (0.5 × 9.81): 219 ÷ 4.9 = 45 kg to 316 ÷ 4.9 = 64 kg. That is weight to be added to, or anchored under, the frame; the overview’s advice to add mass at the base is borne out. Fix the frame to the floor or to a beam where possible.
Racking And Alignment
A rectangular frame with only square joints is a parallelogram waiting to happen; a diagonal brace turns it into rigid triangles (Timber Framing defines a brace as a diagonal timber that prevents racking). The beams that carry the warp, cloth and breast must stay parallel. Floor Loom Construction says: beams must be parallel, the warp and cloth beams must be exactly the same distance apart on both sides, and misalignment of even 5 mm across the width produces uneven cloth. If it means one edge of the warp path is 5 mm longer than the other, then over the 700 mm path used in Shedding the strain differs by 5 ÷ 700 = 0.71% from one edge to the other, as large as the shed’s own 0.66% stretch.
Wood Or Iron
The overview gives two frames: a hardwood frame for looms up to 1 m (Timber Frame Construction) and a cast iron frame for wider looms and higher speeds (Cast Iron Frame). The choice depends less on strength than on stiffness, mass and what the village can make.
What You Need
- Seasoned hardwood or cast iron, whichever the village can make (Seasoning, Casting).
- Joinery that locks, such as pegged mortise-and-tenon (Mortise and Tenon).
- Bracing, a heavy base and floor anchors.
- A level, a string and a long straight edge to check square.
Method: Building To Hold Alignment
Step 1: Compute the shaking force for your slay mass and picks per minute, and the weight needed to hold it.
Step 2: Lay out the frame and brace every plane that could rack.
Step 3: Assemble and measure: diagonals of every rectangle equal, beams parallel, bearings in line.
Step 4: Anchor, then run empty at low speed and watch for creep or rocking.
Step 5: Re-check alignment after a week, since seasoning and loads move joints.
Worked Example
With a slay of 20 kg and r = 0.1 m, running at 100 picks a minute the force is 20 × 0.1 × 109.6 = 219 N. A frame of 30 kg plus loom parts of 15 kg weighs 45 kg, which is just at the limit; run the loom at 120 picks a minute (316 N) and it needs 64 kg, so about 20 kg of ballast or anchors are required. Dimension checks: a 1.0 m by 1.5 m rectangle has diagonals of √(1.0² + 1.5²) = 1.803 m each; if one diagonal reads 1.80 m and the other 1.81 m, they differ by 10 mm and the frame is out of square.
Common Mistakes
- Building the frame by strength only. Stiffness and mass decide whether it runs.
- No bracing, so the frame rhombs under the beat.
- Green timber, which twists as it dries.
- Bolting to a springy floor.
Safety
A frame that walks, racks or tips drags the loom into the weaver
A loom that creeps under 219-316 N can pin a weaver or pull the drive belt off; a rocking frame can fail at a joint with the slay moving. Anchor it, check joints weekly, and keep the stop reachable (Power Drive System). Heavy frame parts are lifted by teams. Children do not work around running looms (Task Assignment by Age).
What’s Next
- Learn next: Timber Frame Construction — building the hardwood frame
- Combine with: Cast Iron Frame — the stiffer, heavier alternative