What’s a Tap & Die?

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Tap and die sets are used to cut threads on blanks and in holes for screws and bolts. The set includes matching taps and dies in common screw sizes, along with wrenches. Taps form female threads by drilling into a pilot hole, while dies form male threads on a hollow rod or screw. They can be used with power tools and lubricant is recommended for metal work. Machinist’s tap guide can assist in manually tapping straight holes.

A tap and die are tools used to cut threads on blanks and in holes to accommodate screws and bolts. Tap and die sets typically consist of matching taps and dies in all common screw sizes, along with wrenches to help the user hold and turn the tap and die. The tap is a metal rod similar to a drill bit that has a cutting edge machined into the rod to form female threads under a surface. A nut is a round piece of metal with a hole in the center; the sides of the hole are machined with a cutting edge to form male threads on a screw or blind rod. Depending on the type of set, the wires can be cut into metals, plastics and wood.

To form the female threads to accept a screw, a shallow recessed pilot hole is drilled into the surface. When tapping hard materials, a hole slightly smaller than the diameter of the tap is drilled to the desired depth of the screw. The tap is inserted into the fixing key that comes with the set and the tip is placed against the hole.

The tap is then rotated and the cutting edge drills into the hole to form the threads. For larger holes or when tapping particularly hard material, smaller taps are sometimes used for the starting hole. Taps with progressively larger tapping diameters are then used until the hole reaches the desired size.

To form the male threads on a hollow rod or screw, a die with threads matching the male is used and inserted into the set wrench designed for the die. The hollow rod or screw is inserted into the mold and the mold is rotated until the desired number of threads are cut into the exterior of the rod or screw. The threaded piece is now ready to be screwed into the threaded hole made by the tap.

For commercial and industrial use, tap and die sets are used with power tools and work the same way as hand sets. The taps are inserted into a drill press or power drill, and the dies are inserted into a lathe or similar rotary tool to accommodate the rod or screw. Complex multiple tap and die setups and specialized machinery are often used for mass production work in factories.

A machinist’s tap guide is sometimes used to assist the operator in manually tapping straight holes into a surface. When working with metal, an oil-based lubricant is typically used on the cock and die. This generally helps reduce friction and stress on the tool.

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