We thought it would be helpful to educate our audience on the difference between a cut tap and a roll tap. This article will primarily focus on the advantages and disadvantages of each tool.
Difference in Cut and Roll Threads
A cut tap and a roll tap both create a thread but in a different manner. Like their names indicate, cut taps cut-removing the material as it establishes a thread, and roll taps (AKA a forming tap) form the material into a thread but without discarding any material. The thread quality produced with these two different tools is dimensionally the same, but structurally different. Because roll taps produce the thread without removing any material, a roll tap creates a more structurally sound thread. However, a roll tap is not always preferable to a cut tap. Forming taps and cut taps are often material specific.
Hole Type and Material Affect Cut and Roll Taps
When deciding between a roll and a cut tap, you need to consider what type of hole you will be threading and into what type of material. A blind hole makes the use of a cut tap problematic. Because the hole has no through end, chip accumulation in the blind hole can lead to tool breakage. Because the forming tap does not produce chips it is preferential to a cut tap, all else held equal.
However, some materials like plastic or cast iron do not lend themselves to being rolled and thus require a cut tap. If the material you are using requires a cut tap on a blind hole, you will need to monitor your pre-tap drill depth. The discarded material will require space to accumulate otherwise it will bind and potentially break your tool. This may be the case if you are threading very soft material like polymers or very hard material like cast iron.
Rolling is the most common type of thread production because of thread strength and chip control. These tools allow for little variance between thread depth and drill depth. However, tool selection is always application driven, and one tool is only ever situationally advantageous over another. In this situation, the material you are machining and the type of hole you are threading reliably dictates your best choice of tool.
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