Press Design

Part of Paper Making

Designing and building presses for papermaking — from simple stone-weight presses to screw presses — and understanding the mechanics of water extraction.

Why This Matters

A press is the piece of equipment that turns papermaking from a slow, weather-dependent process into a reliable production system. Without a press, wet sheets must air-dry in their wet state, which takes hours, produces warped and uneven results, and ties up the mold and felts for the entire drying period. With a press, you mechanically extract 40 to 60 percent of the water from a stack of fresh sheets in minutes, allowing the mold to be returned to service almost immediately and the pressed sheets to dry quickly and flat.

In practical terms, a press increases your paper mill’s output by a factor of three to five compared to air-drying alone. A mill producing 20 sheets per day without a press can produce 80 to 100 sheets with one. For a community that needs paper as genuine infrastructure — for records, maps, books, and communication — this difference is decisive.

Understanding press design principles lets you build a press from available materials and scale it as your community’s needs grow. You do not need metal hardware to build an effective screw press — wood, rope, and basic carpentry can produce a press that serves a community paper mill for years.

The Physics of Paper Pressing

Wet paper contains water in two forms: free water (sitting in the spaces between fibers, held by surface tension) and bound water (chemically associated with the fiber surface). Pressing removes free water efficiently. Bound water can only be removed by drying.

The amount of water removed by pressing depends on:

• Pressure applied (higher pressure removes more water)
• Dwell time (longer pressing removes more water, up to a saturation point)
• Number of pressings (multiple pressings with fresh felts removes progressively more water)
• Felt absorbency (a dry felt absorbs much more water than a wet felt)

There are diminishing returns: the first press removes the most water; the second press removes less; by the fourth or fifth press, almost no additional water is being removed. Practically, two to three pressings with dry or wrung-out felts between pressings is sufficient.

Design 1: Stone Weight Press (Beginner)

Materials needed: Flat boards, heavy stones, a level surface.

Construction: None required beyond finding or cutting flat boards and smooth heavy stones.

Operation: Build your paper post (alternating felts and sheets) on a flat board. Place a flat board on top. Place heavy stones on the top board, stacking until significant weight accumulates. Leave for 15 to 30 minutes. Remove stones, replace felts, re-press.

Performance: Adequate for a small production run of 5 to 10 sheets. The limitation is that pressure is fixed (you can only add so many stones) and distributed unevenly if stones are irregular in shape.

Improvements: Use flat-bottom stone slabs as weights rather than rounded river stones. Ensure the top board is flat and rigid — a bowed board concentrates pressure at the center. Place the press assembly on a stone or concrete floor that can absorb the weight.

Suitable for: Community of 2 to 5 people producing 10 to 30 sheets per day for personal use.

Design 2: Lever Press (Intermediate)

Materials needed: Heavy timber beams (two uprights, one crossbeam, one lever arm), a flat press surface, rope or chain.

Mechanism: A long lever arm pivots over a fulcrum, driving a pressing platen down onto the paper post. Mechanical advantage amplifies the applied force substantially.

Dimensions for a basic lever press:

• Upright posts: 10 to 15 cm diameter, 2 meters tall, set 80 cm apart
• Crossbeam: connects posts at the top, provides anchor point for the lever arm
• Lever arm: 2.5 to 3 meters long, 10 cm × 15 cm cross-section, hardwood
• Fulcrum: a rounded log or stone post set 40 to 50 cm from the press end of the lever
• Press platen: a flat board 5 to 8 cm thick, slightly larger than your mold

Force calculation: With a 3-meter lever arm and fulcrum at 50 cm from the press end, a 70 kg person standing at the far end (250 cm from fulcrum) applies: Force = 70 kg × (250 cm / 50 cm) = 350 kg effective pressing force.

This is substantial — sufficient for a post of 15 to 20 sheets.

Construction steps:

1. Set upright posts firmly in the ground (or bolt to a heavy timber floor sill) 80 cm apart.
2. Mortise and tenon the crossbeam into both uprights at the top.
3. Set the fulcrum post between the uprights, about 50 cm from the press surface.
4. Carve or cut a notch in the lever arm at the fulcrum contact point.
5. Attach the pressing platen to the press end of the lever with a swivel joint (allows the platen to remain horizontal even as the lever angle changes).

Swivel joint for the platen: The pressing platen must remain horizontal as the lever rises and falls. Attach it with a ball-and-socket joint (a rounded wooden ball seated in a matching socket) or simply with a short rope hanging from the lever end — the platen hangs level regardless of lever angle.

Performance: Excellent for medium-scale production. More consistent pressure than stone weights, faster operation, and lever position can be locked (wedge under lever) to maintain pressure for extended dwell times.

Suitable for: Community of 10 to 30 people producing 50 to 200 sheets per day.

Design 3: Screw Press (Advanced)

Materials needed: Heavy hardwood for the frame (oak, ash, or similar), a large hardwood screw and matching nut, a pressing platen.

Mechanism: A large wooden screw runs vertically through a fixed nut. Turning the screw drives the pressing platen down, applying controlled, sustained pressure with very high mechanical advantage.

Screw dimensions: A screw with 5 cm diameter and 3 cm pitch (one full turn advances the screw 3 cm) in a handle 60 cm long applies: Force = Applied Force × (2π × handle radius) / pitch With a 100 N hand force on a 60 cm handle: ≈ 125,000 N = approximately 12.7 tonnes of pressing force.

This vastly exceeds what is needed for paper (or for most other purposes) — even accounting for friction losses in the screw, a good wooden screw press applies several tonnes of pressure easily.

Frame construction:

• Two upright posts (15 to 20 cm diameter hardwood)
• Heavy crossbeam at top, mortised into the uprights
• A lower press bed (heavy flat timber, anchored to the floor or uprights)
• The screw passes through the crossbeam, pressing down onto the platen which rests on the paper post on the lower bed

Carving the screw: This is the technically demanding part. The screw requires:

1. A straight hardwood cylinder, 5 to 8 cm diameter, 50 to 80 cm long (for the screw shaft)
2. A matching threaded nut (a block of hardwood with the matching internal thread)

Screw-cutting method (traditional):

• Wind a paper strip around the cylinder at the desired pitch angle. Mark the helix line with a knife or pencil.
• Carve the thread groove along this line to a depth of approximately 1.5 cm, with angled walls (V-thread or rounded thread).
• For the nut, pack the cylinder thread with clay, press a hardwood blank around it, remove, and let the clay impression guide carving the internal thread.
• Fit the screw in the nut with trial and adjustment. Lubricate with tallow or beeswax.

Alternative screw approach: Two thick ropes wound in a helix around the cylinder can replace carved threads if rope and carving are both available. The rope threads engage matching wooden pegs in the nut. Less precise but functional.

Performance: Excellent for any production scale. Pressure is high, consistent, and lockable. The press can be left under tension for extended dwell times without requiring a person to hold a lever. Standard equipment for all historic paper mills.

Suitable for: Community paper mill producing 200+ sheets per day, or combined use as a printing press, bookbinding press, or fruit press.

Multi-Purpose Press Design

If your community needs to justify the investment in a good screw press, design it for multiple uses:

• Paper pressing: Wide flat platens with drainage gaps at edges
• Fruit and berry pressing (cider, wine, oil): Slotted lower platen allows juice to drain out
• Bookbinding: Narrow platens suitable for pressing book spines
• Textile pressing: Large flat platens for pressing woven cloth

Design the press with interchangeable lower platens and drainage channels that can be opened or closed. The screw mechanism and upper platen remain constant.

Drainage Considerations

During pressing, water expelled from the paper post must drain away freely. If water accumulates around the post, it will wick back into the sheets and reduce pressing effectiveness.

Design the lower press bed with:

• A slight slope (2 to 3 degrees) toward one edge
• A drainage groove or channel around the perimeter
• A bucket or trough positioned to collect drained water (which can be returned to the vat)

For a stone press floor, carve shallow channels. For a wooden press bed, leave a gap of 1 to 2 cm between the edge of the lower platen and the surrounding frame.

Maintenance

Wooden screw presses require regular maintenance. After each session:

• Remove all fiber and paper residue from the press surfaces
• Apply a light coat of tallow or linseed oil to the screw thread and nut to prevent drying and cracking
• Check that the press bed is level — use a water level or plumb line, as a tilted press applies uneven pressure
• Inspect the crossbeam for cracks, especially at the mortise joints — this is the highest-stress component

A well-built screw press, properly maintained, will outlast its builder. Many press components from 17th-century paper mills were still in service 150 years after construction.