Laying Out

a mechanical operation consisting of center punching and scribing lines on the surface of blanks in order to define the dimensions of the part to be machined or mark locations where machining will be done. Machining allowance is removed from blanks along the scribed lines. Laying out is a feature mainly of individual and small-lot production. In large-lot and mass production, laying out is employed in machining articles with special precision requirements, such as dies, interchangeable parts, and casting patterns.

Several methods of laying out exist. The most widespread method uses drawings, from which the dimensions of a part are marked on the blank. Laying out with templates is used in the production of a large batch of parts. In this case, laying out is done only in preparing the template; all of the subsequent operations consist of copying the template outline. Laying out using a model is done by taking the dimensions directly from the part. Laying out by position is used during the assembly of large parts, when the dimensions of one part are laid out in accordance with the dimensions of another part mechanically coupled with it.

Laying out is done on a layout plate. Special devices are used for correct placement of blanks on the layout plate, including prisms, jacks, and pads. Unstable parts are attached with bolts to special try squares or gage blocks. Blanks in the form of rotating bodies that have received preliminary machining between lathe centers or that have been precentered are marked using centering chucks; the chucks are sometimes equipped with spacers and are mounted on the layout plate. Laying out is performed with layout tools.