A project such as the Kansas Statehouse Restoration requires an enormous amount of patternwork. Each separate and distinct component casting that comprises the entire assembled staircase requires a custom pattern to be made. This is true even when there are existing original pieces that merely need copying.

Shrinkage and Draft are the responsible factors. When molten metal cools it converts from a liquid to a crystalline solid. As the molecules of the cooling metal contract to form a solid casting it shrinks. For cast iron the shrinkage rate is one eighth of an inch per linear foot. If the foundry simply placed an original four foot casting in the sand and used the resulting mold to pour an iron casting, it would be 1/2 inch too short overall when it cooled. It is the craft of the patternmaker to cleverly add this shrinkage factor so that the new casting will match the original.

Draft is the other complicating factor. Typical sand molds are made in halves. The pattern must have at least three degrees of draft (sloping sides) to allow it to lift out of each half of the mold. Undercuts in the design will not allow the piece to lift. These must be eliminated, modified or engineered with ‘pick-out” pieces to achieve lift. “Pick-out” pieces are loose pieces pinned to the pattern. When the pattern is removed from the mold the pins release and they are left behind. The “pick-outs” can then be removed leaving behind a more complicated undercut design in the sand mold. The resulting casting has this detail cast into the surface.

Another modification must be made when replicating certain castings. Solid or thick castings tend to develop hot spots in the mold where large amounts of metal gather. As this hotter area cools greater shrinkage occurs leaving an unsightly or malformed blemish in the casting. To eliminate this defect, the pattern can be cored to create a void inside the casting. A shape of bonded sand is suspended in the mold. The molten metal flows around the core. The resulting thinner sections of metal cool at a more even rate giving a uniform surface. The sand core is easily removed from the finished casting.

When asked, “What is the most important skill required to be a patternmaker”, they replied, “Proper use of Machinery”! Lathes, Band Saws, Table Saws and Routers are useful tools to the craftsman but a careless moment can bring about personal injury. Safety in the workplace is stressed at all times. A well thought-out and dimensioned detail drawing is also high on their wish list. It greatly assists in their layout process and reduces the possibility of errors.

Robinson Iron Patternmakers: Barry Turner, Supervisor, Blake Owen, William Vickers, Jerry Wallace, Chris Alford, John Everett

Indispensible tools of the patternmaker - a measured drawing, shrink rule, calculator, and safety glasses.

Safety is a must when operating any shop machinery such as this drill press.

A working pattern is made from an impression of an originally carved and sculpted piece.

Here you see a blue Repro working pattern just after it was poured into a Uralite mold.

Here the “sunflower” pattern is mounted to a board that runs in a box called a “flask”. The handles enable foundrymen to easily separate and/or dump the sand molds.

Even with the most technologically up-to-date equipment, there are many hours spent refining patterns by hand.