Workholding lessons: Turning Performance

Buying a CNC machine is easy. Simply go down to the local distributer, hand over a few bills and become the proud owner of a new machine. Things get a bit more difficult when it comes to programming a CNC machine, but that’s still an easy task to learn. I can take the average person off the street and have them making simple programs in a day or two. Give me a skilled machinist, and that time usually drops to a few hours. Obviously, proficiency and skill are directly proportional to experience and dedication, but programming a CNC machine is not very hard.

I have always been surprised by the number of people who are intimidated by CNC programming when the hard part is getting a workpiece firmly fixed to the machine so the machining can take place. Seriously, the most difficult part of machining (CNC and conventional) is holding the workpiece so that the cutting tool can access the work zone.

I have learned some important lessons over the last 31 years.

Chucks

Keep it simple and make every effort to utilize something that is mass produced and not custom.

If it is a round part, then I try to use a chuck of some kind. Three-jaw chucks, for example, are not just for lathes; they can be used on machining centers, grinders and other machines. A three-jaw chuck can accommodate a range of sizes and is relatively inexpensive and readily available from countless suppliers. When three jaws do not fit the job, chucks also come in two-, six- and four-jaw versions, although these are less common.

Collets

There are also a large variety of devices that use collets for gripping. There is an abundance of collet styles available on the market, and they can be used to grip a large range of diameters as well as non-round geometries like hexagonal and square shapes. Most of the collets
on the market hold an infinite number of sizes inside of their working range. Collets are one the most versatile workholding tools that a shop can purchase.

Vises

Vises are almost as versatile as collets and chucks. Unlike a chuck, a vise does not work well for turning applications, although I’m sure someone has probably mounted one to a faceplate in the past. While they are configured to hold rectilinear parts, a creative machinist can hold almost anything with them. They can be used alone or combined with other vises to hold multiple parts on a machine. Or you could use multiple vises to hold one large part.

Magnetic Chucks

Magnetic chucks typically found on surface grinders are another good choice for workholding. Although they do not grip parts as robustly as the other tools mentioned, they are versatile and can be machined to accept odd shapes. For light milling or turning they are an alternative, especially for small parts that are difficult to hold.