Platen Design

Part of Printing

How to design and build the platen — the flat pressing surface that transfers paper against inked type.

Why This Matters

The platen is the heart of a letterpress printing press. Everything else — the frame, the screw or lever mechanism, the type, the ink — exists to bring the platen into controlled, precise contact with the inked form. A poorly designed or badly constructed platen produces inconsistent impressions, wastes paper, and may damage type. A well-designed platen makes consistent, high-quality printing possible.

In a rebuilding context, the platen is the component most accessible to a capable woodworker or blacksmith. It requires no special machinery to manufacture — careful hand planing, accurate construction, and correct packing are sufficient. Understanding what makes a platen work allows a community to build functional printing equipment from locally available materials.

What the Platen Must Do

The platen must accomplish four things simultaneously:

1. Be flat: A platen that is warped or crowned will apply uneven pressure, causing some parts of the form to print heavily while others barely print.
2. Be rigid: Under printing pressure, the platen must not flex or bend. Flexing causes the center of the impression to be weaker than the edges (or vice versa), and may cause type to shift.
3. Be adjustable: Fine packing material is placed between the platen and the paper (in the tympan) to compensate for type height variations and to achieve the correct impression depth.
4. Allow consistent paper placement: The tympan and frisket (for hand presses) must be attached to or coordinated with the platen to position paper identically for every sheet.

Materials for the Platen

Wood

The simplest and most accessible platen material. Hardwood — oak, maple, beech, or any dense, close-grained hardwood — is preferred. Softwoods compress under repeated printing pressure and lose flatness over time.

Laminated construction: A single thick plank may warp as it responds to humidity changes. A platen built from multiple thin layers glued with alternating grain directions (similar to plywood) is much more dimensionally stable. Build up at least three alternating layers, each 15–20mm thick, for a total thickness of 50–60mm.

Surface preparation: After lamination and curing, face the platen surface with a smoothing plane to achieve flatness. Check with a straightedge in multiple directions. Any detectable hollow or hump should be planed out. Final surface preparation with a cabinet scraper or hand plane produces a flat, smooth surface.

Facing: The working face of a wooden platen is usually covered with a thin, hard material to prevent wear and provide a consistent surface. Traditional options include a sheet of smooth iron or brass tacked to the face, or a layer of very hard paste (a mixture of boiled linseed oil and pumice or fine sand, applied repeatedly until the surface is glassy hard).

Stone

A flat slab of dense limestone, marble, or granite makes an excellent platen. Stone is naturally rigid, dense, and easily kept flat. It was used in early printing presses before iron became common.

Stone platens require no construction — a naturally flat slab of appropriate size, smoothed and polished on the working face, is functional. The main limitation is weight: a stone platen large enough for folio printing may weigh 15–30 kg, requiring robust press framing and mechanical advantage to operate.

Cast Iron or Wrought Iron

The standard material for industrial-era printing presses. Iron platens are durable, stable, and can be precision-ground flat. They require a foundry and pattern-making skills to produce, which places them beyond the immediate capabilities of most rebuilding communities.

However, salvaged iron — flat sections cut from machinery, engine blocks, or structural members — can be repurposed as platens if they are flat or can be made flat. A machined iron surface is extremely durable and resistant to wear.

Sizing the Platen

The platen must be larger than the form (the area of set type) in all dimensions. A platen that is the same size as or smaller than the form cannot distribute pressure evenly across the edges.

Standard practice: the platen should extend at least 50mm beyond the form in all directions. For a form that is 150mm × 200mm, the platen should be at least 250mm × 300mm.

For a general-purpose press intended to print folio sheets (roughly 200mm × 300mm printing area), a platen of 300mm × 420mm provides adequate margin.

Tympan and Packing

The tympan is a frame hinged to the press (or held against the platen) that holds the paper and carries the packing layers. The packing is where impression pressure is fine-tuned.

Basic Tympan Construction

For a wooden press:

1. Build a rectangular frame from straight-grained hardwood, mortise and tenon jointed at corners, the same width and height as the platen.
2. Stretch heavy cloth (canvas or heavy linen) tightly across the face, tacking it to the frame edges all the way around.
3. The cloth surface receives the packing.

Packing Layers

Packing consists of thin layers of material placed between the tympan cloth and the paper, which the platen compresses against the type. The total thickness of packing determines the impression depth and adjusts for uneven type height.

Hard packing (for crisp, precise impressions): Multiple sheets of smooth, hard paper (card, calendar board). Hard packing concentrates pressure precisely at the type face. Good for sharp text, fine detail.

Soft packing (for uneven type or decorative work): Includes a layer of felt, thin cloth, or rubber sheet under the top hard layers. Soft packing compensates for slight variations in type height (worn type, uneven setting) by conforming slightly to the surface. Less precise than hard packing but more forgiving.

Building the packing: Start with two sheets of smooth hard paper as the base. Pull a test impression and inspect it. If some areas print heavily and others lightly, add a thin piece of packing material (“overlay”) positioned precisely over the light areas. This targeted shimming is called “makeready” and is the central skill of press preparation.

Makeready

Makeready is the process of achieving a uniform impression across the entire form by adding and subtracting packing material in localized areas. A skilled pressman can make ready a complex form in 15–30 minutes; a poorly made-ready form wastes paper and produces inconsistent output regardless of ink quality.

Makeready procedure:

1. Pull a first impression. Note any areas of light or heavy printing.
2. On a waste sheet, cut out the shapes of areas that printed too lightly.
3. Affix these cut-outs to the packing at the corresponding positions.
4. Pull another impression. The light areas should now print stronger.
5. Repeat, adjusting, until the entire form prints uniformly.

Platen Alignment and Adjustment

The platen must descend parallel to the form surface. If the platen is tilted, one edge of the form will receive more pressure than the other, and impression pressure will never be uniform regardless of makeready efforts.

Testing Parallelism

1. Ink the form lightly with a very thin ink film.
2. Bring the platen down very gently to just barely contact the form.
3. Without applying full pressure, back off and inspect the platen face: ink transfer spots show where the platen contacted first.
4. If only one corner or one edge shows ink, the platen is tilted in that direction.

Adjusting Alignment

On a wooden press with bolt-adjusted platen:

• Add thin shims (folded paper, thin wood veneer) under the platen mounting at the corners that contacted too late (showed no ink).
• Re-test and adjust until ink transfer is uniform across the entire face.

This alignment process must be repeated whenever the press is disassembled, moved, or when the platen is replaced. A press that is correctly aligned but then moved to a new location — placed on an uneven floor, or with one leg shimmed differently than before — may need realignment.

Common Platen Problems

Printing heavier at center than at edges: Platen flexing under pressure (too thin or insufficiently rigid). Solution: add thickness, laminate, or face with a rigid material. Alternatively, reduce packing to lower impression pressure.

Printing heavier at edges than center: Platen crowned (slightly curved convex at center). Plane the center of the platen face very carefully to flatten the crown. Check with a straightedge and retest.

One-sided impression: Platen tilted. Align as described above.

Impression varies from sheet to sheet: Platen mounting not rigid — the platen shifts slightly between impressions. Check all fasteners, add bracing, or redesign the platen attachment.

A well-designed, correctly installed platen is a long-term investment. Built from quality materials and maintained in alignment, it will serve a print shop for decades.