Equipment and Tooling

Small Wonders – Circuit Board Drills

Do you ever need to drill small-diameter holes? Yes? How about really small holes, say, ones the size of a cricket’s leg? If you answered yes again, you understand the challenges involved in producing tiny holes.

Very small holes often require you to contend with tool breakage, the high cost and scarcity of drill bits, and insufficient spindle speeds.

One solution to these problems is to use circuit board drills. CB drills, as their name implies, produce holes in printed circuit boards. And since a lot of circuit boards are being manufactured these days, CB drills are readily available.

They typically are mounted in machine tools designed specifically for the production of circuit boards. These quick and highly accurate machines have multiple spindles that can run at speeds exceeding 100,000 rpm.

Inspecting a CB drill under a microscope reveals a marvel of modern manufacturing. It seems to be an impossibly small tool to incorporate polished flutes and a 4-facet point that is self-centering and free cutting.

CB drills have a standard 1/8″-dia. shank and an overall length of 1 1/2″. They also have a higher length-to-diameter ratio than conventional drills. This is because when circuit boards are drilled, several units are stacked together. The cutting range for CB drills starts at 0.2500″ and goes all the way down to 0.0039″, which is roughly the diameter of a human hair.

Most CB drills are made of solid carbide. Less expensive ones, those with stainless steel shanks, are also available. The drills come with or without a plastic ring, which is attached to the shank 0.8000″ from the tip of the drill and serves as a locating reference. By seating the ring against the face of the collet, the machinist can quickly and easily replace a broken drill without having to recalibrate the length.

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