Machine Design

How-to, in-depth technical articles for machine design engineers

Salary Expectation

8 things to know about the interview question "What's your salary expectation"?

Hydraulics & Pneumatics

For design and manufacturing engineers involved in buying or specifying fluid power components and systems.

Reinforced Plastics

Informed and impartial coverage on the global composites industry.

more free magazines
Introduction

Drilling, tapping, counterboring, and countersinking are the usual operations done in sheet metals.

Drilling: Drilling is done in sheet metal only when piercing cannot deliver the accuracy required. For example, on a formed part, when holes on different features need to be coaxial, the accuracy obtained by machining may be required.

Tapping: Tapping can be done using cut threads or formed threads. Formed threads (thread rolling) is preferable for the following reasons:

  • Thread rolling is faster than cutting.

  • Fewer burrs are generated, so no clean up is required or risk of future hazards such as shorting with electronic components.

  • Larger sized holes are required for thread rolling vs. tapping, resulting in improved tap life.

  • Rolled threads are stronger due to cold working. Typically, rolled threads are 20% stronger than cut threads.

  • For very thin stock, either threaded fasteners such as clinch nuts, or forming thread in extruded holes is recommended.

    OR

  • The material is upset in the sheet metal hole to form one thread pitch.

Counterboring: Counterboring is often done to provide clearance and a bearing surface for the fastener's head.

Countersinking: Countersinking allows for flush mounting of flat head fasteners. Countersinking cannot always be done for very thin stock or for very large fasteners.

Glossary