Threading & Tapping

This article reviews the causes of skin irritation suffered by some shop workers, with special attention paid to skin conditions that result from poorly maintained metalcutting fluids. The article also discusses the factors that can aggravate skin problems and suggests ways that workers can protect themselves from skin irritants.

Traditional tap/drill charts recommend drill diameters for each size of tapped hole. But, according to this article, these recommendations are based on the size holes that were typically produced by less-accurate tools and processes used in the past. This article suggests guidelines for producing holes that will, in turn, produce correctly sized tapped holes.

There are several types of feed units for drilling and tapping on the market, varying in capability and the type of drive. This article discusses the difference between units and suggests questions users should ask themselves before selecting a unit. Factors to be considered include the volume of production, cost engineering and tool requirements.

The advent of CNCs made new threadmaking technologies practical. Among these technologies are rigid tapping and thread milling. This article describes the uses, techniques and benefits of these two threadmaking methods.

There are some tapping situations that call for a rigid tapholder and some that call for a length-compensating holder. Often the choice depends on the capabilities of the machine and the CNC driving the tap. This article discusses why a machinist might choose one type of tapholder or the other.

Internal threads can end up undersized because of the work material's properties or because of changes to the hole's dimensions caused by plating or heat-treating processes performed after tapping. This article explains H- and D-limits and how to use them to specify a tap that will produce the right size thread, regardless of any post-tapping operations.

Roll-forming taps produce internal threads by displacing the metal under pressure rather than cutting it. This article explains how to perform the operation to achieve good quality threads. Formulas and charts help the user calculate the proper size hole and the size of tap to use for a desired thread.

Deep-hole tapping raises chip evacuation, lubrication, and torque risk. This guide covers practical depth limits, tap selection, and process controls for deeper threaded holes.

Thread rolling produces external threads by forming the profile instead of cutting it. This guide covers where CNC thread rolling fits, why it can outperform cutting, and what shops should watch in setup.

The choice of tapping driver, the component between the spindle and the tap, can affect the quality and accuracy of the threads as well as the rate of wear on the tap and the machine tool. This article discusses how features such as length compensation and self-reversing protect against damage caused by machine and tool errors.