Roll Forming Taps vs. Cutting Thread Taps on a CNC Mill

Cut taps and form taps both produce internal threads, but they work in fundamentally different ways. A cut tap removes material to create the thread, while a form tap displaces material under pressure.

The tools also look different. A cut tap has incomplete lead threads near its tip and flutes that provide clearance for chips. A form tap has no chip-clearing flutes and maintains a more consistent profile from bottom to top.

Cut Taps

Cut taps have been the conventional choice for decades. The process is straightforward: drill the correct tap-size hole deep enough to accommodate the required thread length, then run the tap into the hole.

Depending on the CNC machine and workpiece material, tapping may be limited to roughly 200–300 RPM. Rigid tapping on newer CNC mills permits higher spindle speeds and can significantly reduce cycle time.

Cut taps are especially useful for through-holes because chips can move out through the bottom. This reduces the need to remove chips from inside the hole, although the tap must not collide with a table or fixture beneath the workpiece.

Because these taps cut material away, they can often operate with a wider range of coolants, particularly in softer materials such as aluminum.

Form Taps

Form taps create threads by displacing material rather than cutting it. Consequently, they produce no chips.

The formed threads are generally stronger because the material is compressed into the thread profile instead of being severed. Form taps themselves are also strong and can offer longer tool life, reducing tap breakage and replacement costs.

Form taps can often run at higher speeds than cut taps, helping shorten tapping cycles.

Lubrication and Setup Requirements

The forming process places greater pressure on both the tool and the hole. It therefore requires coolant or tapping oil with high lubricity. Inadequate lubrication increases tool load and can eventually break the tap.

Lubrication is especially important with small form taps, such as M3 taps, because there is little space for coolant to reach the working surfaces effectively.

The entrance countersink must also be large enough. Otherwise, displaced material can rise above the workpiece surface at the first thread and interfere with a mating component.

Practical Selection

• Choose a cut tap when chip evacuation is manageable, the application involves through-holes, or available lubrication is limited.
• Choose a form tap when chip-free operation, stronger threads, longer tool life, or faster cycles are priorities and the material is suitable for forming.

If taps continue to break, experiment carefully with spindle speed, lubrication, hole preparation, and tap selection.