Cross-Hole Deburring In-Process

One of the most nagging problems that metal-working shops face is dealing with burrs. Of particular challenge is deburring of the intersection of cross-drilled holes.

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One of the most nagging problems that metalworking shops face is dealing with burrs. Of particular challenge is deburring of the intersection of cross-drilled holes.

Despite the best efforts of machinists and programmers, burrs are virtually impossible to eliminate when cross-drilled holes intersect. Multiple drill passes can help reduce the burr, but if the part specification calls for burr-free, additional intervention is generally needed.

Most shops are familiar with the conventional methods of deburring. These include grit blasting, extrude honing, thermal deburring and, of course, the ancient but effective methods using knives, stones, brushes, files and good old elbow grease.

All of these different deburring processes work well, to varying degrees, but they share one unfortunate thing in common: They must be performed off-line. As such, deburring becomes a separate manufacturing step, a secondary or tertiary operation, that requires at least extra handling, labor, movement, and in some cases, additional capital equipment.

Often deburring is outsourced to specialty shops. Subbing out the work, of course, prolongs the overall manufacturing process by putting the delivery of quoted work into another shop's schedule. Moreover, prolonging the delivery of parts is counter to most industry trends.

J.W. Done Company (Foster City, California) has developed a deburring tool that can accomplish the task of cleaning up burrs created by cross-drilled holes in-process. Called Orbitool, it's designed to mount into a toolholder on a lathe or machining center and operate basically like a conventional cutting tool. It removes burrs from the intersection of holes and can be tailored to leave a minimally broken edge or blended radius.

An Orbitool consists of a hemispherical shaped cutter and a disk fixed on the end of a shaft. The cutter and disk resemble an upside down bowl on a saucer. The disk is larger than the cutter, which is a key to the tool's operation. The shaft is mounted in a flexible coupling, and it is mounted in a toolholder on a machine. Standard tools are available with carbide cutters. Other materials can be used for cutters as well.

In operation, the tool is partially inserted in one of the intersecting bores, close to the intersection. The tool is then moved laterally until the disk contacts the wall of the bore. This contact causes the flexible coupling to deflect slightly. (See Figure 1.)

At this point in the process the cutter is rotated and fed down into the bore using a helical interpolation routine. To prevent chatter, the cutter rotation and helical direction should be the same.

Using the helical interpolation, the cutter sweeps around the bore (Figure 2). Because the disk is slightly larger than the cutter, it keeps the abrasive surface of the cutter from contacting the bore until the tool hits the intersection. The disk is smooth and radiused to prevent marring the wall of the bore.

As the disk approaches the edge of the bore's intersection, it falls off the bore wall and allows the cutter, which is under load from the deflected flexible coupling, to machine the burr. Like a cam follower, the disk traces the contour of the cross-hole intersection so only the burred areas come in contact with the cutter.

When the operation is complete, the cutter is moved to the center of the bore, clear of the wall, and retracted. It's a nifty tool for deburring problematic cross-holes, and it can also be applied in tapped holes to clean up lead and finish threads.

The company offers three standard cutter sizes, 1/8, 1/4 and 3/8 inch nominal diameters. While these three diameter cutters are the current standard offering, the concept is scalable, and different sizes can be made if requested. Each tool works in a range of diameters so exact matching of the cutter diameter to the bore is not necessary.

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