Drilling

Machinists have the choice of four basic types of drills that are made with carbide cutting edges: solid carbide drills, drills with indexable-inserts, drills with brazed carbide tips and drills with exchangeable solid-carbide tips. Each of these drills has advantages for specific applications.

Solid-carbide drills are made to be used on modern machining centers. These drills are manufactured with fine-grain carbide and titanium aluminum nitride (TiAlN) coatings to provide long tool life. As self-centering drills, they have a specially designed edges that help to control chips and chip evacuation in most workpiece materials. The self-centering geometry and fine tolerances of solid-carbide drills ensure quality holes without additional machining.

Indexable-insert drills cover a broad range of diameters with depths two times diameter to five times diameter. They may be used for rotating applications as well as in lathes.

Drills with brazed carbide tips rely on the strong connection of the brazed tips to the drill bodies. 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 additional finishing operations. These drills are available with through-the-tool coolant, and can be used in machining centers, CNC lathes or other machines that have sufficient stability and rpm.

Drills that have exchangeable solid-carbide tips incorporate a steel body with the exchangeable tips that are known as crowns. These tools offer the precision of brazed drills, and offer increased productivity at reduced operating costs. The carbide crowns used with this new generation of drilling tools are available in precise size increments and have a self-centering geometry to produce close diameter tolerances.

Drilling tolerances and machine stability

REF: www.cutting-tool.americanmachinist.com