American Machinist

Drilling do's and don'ts: make holemaking more productive. (Holemaking).

Many shops mistakenly believe that drilling operations must be done at comparatively low feeds and speeds. While this was once true, the same can't be said of today's carbide drills. In fact, users can greatly improve productivity and reduce overall cost-per-hole with the right choice of drills.

End users have the choice of four basic types of drills with carbide cutting edges: solid-carbide, indexable-insert, brazed carbide-tip, and exchangeable solid, carbide tip. Each has its advantages in specific applications.

The first, solid-carbide drills, are made for use on modern machining centers. Manufactured with fine-grain carbide and TiAlN coatings for long tool life, these self-centering drills employ a specially designed edge for excellent chip control and evacuation in most workpiece materials. The self-centering geometry and fine tolerances of solid-carbide drills ensure quality holes without any further machining.

Indexable-insert drills cover a broad range of diameters with depths from 2 x D to 5 x D. They may be used for rotating applications as well as in lathes.

With brazed carbide-tip drills, there's a strong connection of the brazed carbide to the drill body. These tools use a self-centering geometry for low cutting forces and good chip control in most workpiece materials. Brazed drills produce holes with relatively high surface finish, close diameter tolerances, and good positioning accuracy without further finishing operations. …

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