Laser Focus World

Semiconductors, medical equipment, lasers, optics and aviation and aerospace.

Chemical Engineering

The industry gateway for chemical engineering and plant operations.

Quality Magazine

Techniques to improve quality on the shop floor and in manufacturing planning.

Autonomous Vehicle Engineering

The No. 1 media source for those developing the next generation mobility solutions.

more free magazines

Materials

Design

Processes

Units

Formulas

Math
Parallelism vs. Flatness
One common area of confusion within GDT is between parallelism and flatness. With, parallelism, a reference is made to a datum plane, while flatness is independent of a datum. Figure PF1.1 shows a block on a surface plate whose three points of contact define the -A- datum plane. As specified, the opposite face of the block must lie within two planes which straddle a plane parallel to and 2.0 from -A- and .125 to either side of it.

Figure PF1.1


Figure PF1.2 shows a flatness specification on the same surface. No datum plane is involved. A "best fit" plane (3 point contact) defines the mid-plane, and all surface points must lie between two planes which are parallel to this plane, and .125 to either side of it.

Figure PF1.2

Glossary