Manufacturing: Surface Finishing

Honing

The honing process is used to obtain precise dimensions and surfaces in cylindrical shapes with a wide range of diameters. This applies to parts such as Hydraulic Cylinders, Pistons, Bearing Bores, Pin Holes and to some external cylindrical surfaces. The honing process offers advantages of low capital equipment cost, high metal removal rates, and extreme accuracy of 0.001mm (0.00004´´) in a wide variety of materials.

Other advantages include the ability to create round and straight bores in relatively long workpieces. Workpiece bore length-to-diameter ratios of 1.5:1 and longer are ideal for the process. Shorter bore lengths can be accommodated by stacking workpieces in special fixturing.

Honing can correct parts that are not square, within limits. Understanding the abilities of honing to correct out-of-squareness requires an explanation of the principles of honing.

How honing works

The abrasive action of the honing tool removes material from the workpiece's inside diameter. The tool rotates and expands while the workpiece reciprocates (stroking) back and forth. For example, tolerances of 0.003mm (0.0001´´) round and straight can be achieved in production using special fixturing. To achieve such close tolerances, the workpiece must be allowed to "float" or move in three axes. This movement is the single most important point in achieving the closer tolerances required in industry today.

To correct out-of-squareness, the workpiece must be positioned against a flat face plate that is perpendicular to the machine spindle axis. This, of course, reduces one of the three axes of movement, thus reducing the amount of movement or "float."