Tapping operation tips

How to tap threads

The success of any tapping operation depends on a number of factors, all of which affect the quality of the finished product. Follow these steps to ensure a good tapping thread operation.

1. Select the correct tap for the component material and the type of hole to thread. See section How to choose the right type of tap.
2. Ensure that the component is securely clamped—lateral movement may cause tap breakage or poor quality threads.
3. Select the correct drill for the component material and drill size.
4. Always ensure that work hardening of the component material is kept to a minimum (check the drill condition).
5. Select the correct cutting speed.
6. Use the appropriate cutting fluid for the application. See section "How to use coolant in tapping operations" here below.
7. In NC applications, ensure that the feed value chosen for the program is correct. When using a floating tapping attachment, 95–97% of the pitch is recommended to allow the tap to generate its own pitch and hold the tap in a good quality torque limiting tapping attachment. This ensures free axial movement of the tap and presents it squarely to the hole. It also protects the tap from breakage if accidentally “bottomed” in a blind hole.

How to use coolant in tapping operations

Coolant is important for a successful performance when tapping threads. The coolant supply influences chip evacuation, thread quality, and tool life and can be either internal or external.

Internal coolant supply

Internal coolant supply is always preferred for improving chip evacuation, especially when tapping long chipping materials and deeper holes (2–3 × D). Wear on the cutting edge is also reduced thanks to a good cooling effect on the cutting zone.

External coolant supply

External coolant supply is the most common coolant method and can be used when chip formation is good. To improve chip evacuation, at least one coolant nozzle (two if the drill is stationary) should be directed closely to the tool axis.

Different cutting fluid/emulsion

There are different alternatives to cutting fluids: mineral-based oil, synthetic coolant, semi-synthetic cutting fluid, vegetable-based oil, and straight oil. It is important to always be aware of the type of cutting fluid used in the machine as well as the oil content.

Mineral oil-based emulsion

• Good cutting properties
• Most common in tapping operations
• Oil content 5–7% for steel8–12% for tough steels and stainless steel
• Normally a stable emulsion and good for the machine

Synthetic coolant

• Not as good cutting properties as other coolants for tapping operations
• It is crucial to always check with the emulsion supplier for mixing instructions and other tapping recommendations
• Stable but can be tough on the machine

Semi-synthetic coolant/emulsion

• Rather new to the market
• Usually good cutting properties
• Often recommended for a wide range of materials
• Recommended for all types of machining
• Stable emulsion

Vegetable oil-based emulsion

• Best cutting properties of all emulsions for tapping operations
• Not that common in workshops
• Oil content 6–8% for stainless steel10–12% for tough stainless steel and exotic steel

Straight oil

• Mostly used in turning machines and small part machines
• Provides optimal cutting conditions in tapping operations
• Stable emulsion

Always check with the supplier for the recommended mixing instructions and oil content.