Workholding: Hold Small Round Parts

This article originally appeared in Modern Machine Shop
Columns Post: 7/2/1999     STAN SEIBERT

When you need to make small parts, the size range of the 5C collet is where the best variety and value exist in machine tools and accessories. You don't want to sink capital into expensive, specialized machinery that will run nothing but small parts. But a 5C collet is pretty big compared to your 1/8-inch diameter part.

An adapter is available, however, that renders a common 5C machine tool capable of handling very small diameter parts. The new small parts adapter, manufactured by Masa Machine Tool Accessories, Oceanside, California, fits in any machine's 5C collet closer, just like a standard 5C collet, without any modifications or special mounting procedures.

With the adapter, any machine with a 5C collet closer can chuck workpieces in the range of 0.010 to 0.375-inch diameter (0.25 to 10 mm). Yes, I truly mean that a common CNC turret lathe with one-inch shank tooling and a brutally powerful hydraulic 5C collet closer can easily chuck fragile 0.010-inch diameter workpieces effectively and repeatably, without damage. Of course, I don't recommend using a machine like that to make a part that small. However, this shows the level of control that the adapter provides.

According to Matt Saccomanno, president of Masa Machine Tool Accessories, he conceived the adapter in utter frustration while trying to set up machinery in his own shop for secondary operations on small parts. "This setup would be so easy if I didn't have to deal with that stupid fixture," he recalls thinking at the time. The only purpose for the fixture was to allow the endmill to reach down to the part without hitting the 5C collet nose with the spindle. "Well, I finally got the fixture to work that day, but more important, an idea was born so I wouldn't have to deal with that problem again," he says. "The idea eventually became the Masa small parts adapter. Then the uses for the adapter went far beyond my original ideas. Soon they were all over the shop—in the tool grinding room, on CNC lathes, CNC mills, as well as in `second op.'"

The are several reasons why this approach to small part holding works. For one, the workholding system must be as small as possible to allow small tooling to be closely snubbed within the toolholder, yet still be able to reach the workpiece. This is accomplished by the extended nose of the adapter.

Moreover, chucking force control is a big issue with small parts manufacturing. Most 5C closer mechanisms and the collets themselves are too bulky to permit reliable operation at pressures low enough to prevent damage to smaller workpieces. The Masa adapter has self-contained chucking force control. Regardless of how powerful the machine's closer mechanism can get, infinitely variable drawstroke control is provided. And it does so with a high degree of accuracy and concentricity.

The quick interchangeability of the adapter allows a machinist to go from a 0.050-inch diameter part back up to a 1-inch diameter part with no more hassle than the normal changing of a collet.

Because the adapter fits in any 5C collet closer, it can be used in a range of applications. Here are just a few examples:

A job shop was cross drilling ¼-inch diameter stainless steel microwave couplers and had to center drill to prevent wandering of the final drill. Now, due to the extended nose of the adapter, it can chuck the final drill so it protrudes only 0.38 inch from the drilling spindle, which makes it rigid enough to eliminate center drilling. The company also uses the adapter frequently for milling operations.

A manufacturer of precision dental implants was getting complaints about cosmetic problems on the external surfaces of its parts due to the chucking for a secondary operation on a CNC turret lathe. The company tried many different schemes to control the chucking force of its pneumatic collet closers, but to no avail. With the adapter, however, now it can leave the air pressure set at a "normal" range, while it has infinite adjustment of chucking force.

A tool room grinder had trouble making specialized carbide form drills. The work head would interfere with the grinding wheel, which made some of the angle and relief grinds very difficult. The extended nose of the adapter allows the grinding wheel to get in much closer. Setup is simpler. Wheel dressing is minimized. The drills can be chucked more rigidly. Also, with the self-contained locking feature of the adapter, a drill can be removed from the grinder without losing orientation or concentricity.

Most likely, if you make parts less than ½-inch in diameter, the adapter can help you do it more effectively.