Cast iron side frames in an A shape, joined by bolted iron cross-members, are much stiffer than timber and suit looms 1-2 m wide and faster running. The price is mass and foundry capacity: an assumed pair of side frames weighs about 150 kg, one frame needs a furnace able to pour about 77 kg of iron at 1,150-1,200 C in one go, and cast iron is brittle, so bolt holes and shuttle impacts need care.
Part of Power Loom Construction
A cast iron loom frame for wider cloth and higher speeds, and the foundry work it demands.
What The Overview Specifies
The overview’s iron frame has cast iron side frames of A-frame shape and iron cross-members bolted between them. It is much stiffer than wood and allows higher operating speeds, and it is meant for looms of 1-2 m weaving width. The structural requirements are the same as the timber frame’s (Loom Frame Design): square, parallel, braced and heavy enough to take the slay’s push.
The Casting Is The Hard Part
Casting lists cast iron as melting at 1,150-1,200 C with excellent flow, which is why it fills complex moulds, and as too brittle to hammer. Sand Casting gives the pattern allowances: cast iron shrinks 1.0% (10 mm per metre), so a pattern for a 1.5 m member is made 1.5 × 1.01 = 1.515 m, and machined faces need an extra 2-3 mm. Seats for bearings and bolt faces are the surfaces to machine (Metal Turning). Cast iron’s density in the flywheel article is 7,200 kg per cubic metre (Flywheel Design).
Mass check on assumed dimensions: an A-frame 1.5 m tall and 1.2 m across the base has two legs of √(1.5² + 0.6²) = 1.62 m and a cross-tie of 1.2 m, together 4.43 m of member. At an assumed 60 × 40 mm section that is 4.43 × 0.06 × 0.04 = 0.0107 m³, and × 7,200 = 77 kg per side frame, 154 kg for two (about 150 kg). Pouring one side frame means a furnace that melts at least 77 kg of iron at once, plus the gating, with enough heat to stay fluid to the farthest corner. The pattern, the sand mould and the cooling time all scale with that mass. A village that has not cast a 77 kg piece before should start with smaller parts.
Brittle Iron Needs Careful Details
Cast iron breaks without bending. Keep section changes gradual, put fillets in inside corners, and avoid thin lugs next to bolt holes. Use bolts of wrought iron or steel through bosses, not hammered rivets. The shuttle’s blow on the box and the slay’s push are shocks the iron must take in compression where possible. Bolt cross-members into machined seats, not into rough casting skin.
What You Need
- A pattern of the side frame, oversize by 1.0% (Sand Casting).
- Sand, flasks, a furnace and a means to pour a heavy casting.
- Machining to finish the bearing and bolt seats.
- Wrought iron bolts and cross-members.
Method: From Pattern To Frame
Step 1: Decide whether iron is needed. A timber frame serves looms up to 1 m (Timber Frame Construction); the iron frame is for wider looms or faster running.
Step 2: Make the pattern with the 1.0% allowance and the 2-3 mm machining allowance.
Step 3: Mould and pour following the cooling times in the sand-casting article, which gives 30-60 minutes minimum for cast iron.
Step 4: Clean, inspect for cracks and cold shuts, and machine the seats.
Step 5: Assemble with cross-members, set square, anchor and ballast.
Worked Example
A frame member designed as 1.500 m is cast from a pattern of 1.515 m and shrinks back to 1.500 m as it cools. If the pattern were made without the allowance the finished member would be 1.5 × 0.99 = 1.485 m, 15 mm short, which would put the beams out of square far beyond the 5 mm that spoils cloth (Floor Loom Construction).
Common Mistakes
- Making the pattern to finished size.
- A casting poured without the cooling time, which cracks.
- Sharp internal corners, where cracks start.
- Over-tightened bolts through thin cast lugs.
Safety
Molten iron and a 77 kg casting
Iron at 1,150-1,200 C burns through skin and boots, spits when it meets damp sand or tools, and a lifted mould of this size crushes feet. Dry every tool and mould, wear face and foot protection, and keep onlookers and children away from the pour (Task Assignment by Age). A finished frame is heavy; move it by a team with levers and blocking, not by hand.
What’s Next
- Learn next: Heddle Construction — what the frame carries
- Combine with: Loom Frame Design — the forces the iron must resist