What is the best way to learn something? For my money, it's hard to beat the "just do it" method, which may land you in hot water once in a while. So be it.

The following are some basic shop practices for newcomers. The information is also about avoiding blunders. Not all mistakes in a machine shop are of the dimensional type. Blowing chips on the guy next to you is an example of a nondimensional mistake. By learning some of these basics, newcomers will be in a better position to work independently and with other shop personnel.

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I've worked with two people who severely ground down their thumbs trying to deburr the edges of a thin plate in a disc sander. As they were sanding an edge, the plate got sucked into the small opening between the table and the disc, which pulled the plate and their thumbs into the disc. If you are going to deburr a plate with a disc sander, make sure you hold the plate above the support table.

Nominal sizes are convenient labels used to discuss part sizes that, in reality, nobody will ever hit. However slight, there is always some tolerance or error in every machined part. People sometimes say, "Just shoot for the nominal." That means if the nominal size you're working to is 1/2", then you need to do your best, within reason, to machine the part to 1/2", taking into account the type of machining process being used. You wouldn't be expected to hold 1/2" nominal size as closely with a milling machine as you would with a surface grinder.

Absolute dimensions refer to distances from a single origin to a point or feature. Incremental dimensions refer to distances from one feature or point to another. Most digital readouts can be switched back and forth. One example where switching can be useful is if the centers of a series of bolt-circle patterns are dimensioned from one corner of a plate. The centers of the patterns can be dialed off in "absolute" and then, by switching to "incremental," the holes can be dialed off incrementally.

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Lofted surfaces are surfaces created by sweeping or blending different profiles from different planes. For example, a lofted surface can be created by blending a square in one plane with a circle in another parallel plane.

I prefer leaving all edges sharp when making mold parts until I can carefully examine and detail them on a bench. Most machinists are so accustomed to filing edges that they do so automatically. However, when making mold parts, filed edges can spell disaster--especially on core and cavity details. Parting lines, shutoffs and other corners and edges on mold parts may have to be perfectly sharp to prevent flash and maintain part integrity.

This ProShop Machinist Article is adapted from information in the book "Machine Shop Trade Secrets: A Guide to Manufacturing Machine Shop Practices" published by ProShop Publishing. A special thanks to 'Cutting Tool Engineering Magazine' for teaming up with James A. Harvey to produce this article.