Mold & die industry often deals with ultra-hard materials that require specific taps to face the resistance of steels to be cut. UH-CT carbide hand taps are designed for tapping hardened steel and extremely high hardness steel up to 60 HRC. This article gives some practical advice for getting the most from these tools.
Bored hole size
Drill the bored hole as large as possible within thread tolerance because it helps reduce the torque load and tapping becomes easier. To learn more about the importance of bored hole size, see this link.
Note that if the internal thread requirement is specified as 6H or class 2, drill the bored hole as close to the maximum minor diameter of the thread tolerance as possible. This is possible because the design of the tip diameter of UH-CT taps is as close as possible to the maximum minor diameter of the 6H internal thread and it is larger than conventional taps.
Bored hole depth
If UH-CT taps bind on the chips accumulated in the bottom of the hole, chipping problems may occur. Depth of the bored hole must be deeper than 5 threads, i.e., longer than the chamfer length of UH-CT taps.
If it is not possible to drill such a deep bored hole, clear chips after tapping the half of the overall tapping length and continue to tap again to the bottom. The bored hole table is a useful tool that helps you easily find the most suitable bored hole diameter for the selected size of the tap you are working with. You can download your copy for free here.
Run-out, bent holes, and cutting speed
Ensure that there is no spindle run-out or misalignment between the centre of the holes and the machine spindle which may lead to chipping carbide UH-CT taps. Use a recommended tapping speed from 1 to 1.5 m/min.