A double-margin tool usually produces a better hole and more stable drilling conditions. The tool design also has a great impact on hole quality. Solid-carbide drills tend to leave a more cylindrical hole with a better surface finish than HSS or HSS-E tools because of the higher stiffness of the tool material. Stamping, flame or laser cutting, casting, milling, and drilling are common holemaking methods that yield completely different bore conditions. The first part of the threading process is always creating the hole. It is crucial to look at the tapping process, not just the tool, to achieve a good finished product. A tap failure is usually blamed on a “bad” tool when, most likely, there is nothing wrong with the tap itself it just might not be ideal for the machining conditions. Other factors such as toolholding, workholding, machine condition, and lubrication also can have a significant effect on the tapping operation.

Thread mills will usually overcome the issues that can cause taps to fail, making them an attractive option for most applications. Of all the threadmaking processes, tapping seems to suffer the most from this oversight.

When diagnosing problems with internal threading, a machinist often overlooks the size and condition of the hole before threading. Roll form tapping as a chipless threading process requires excellent hole size and quality.

Form tap vs cut tap