What is a Polygon Profile?

The unique feature of the machine which made this possible was its wheelhead. Using a mechanical drive system, the wheelhead could be set to move the grinding wheel in an elliptical path to keep the wheel to the norm of the centerline of the workpiece as the work was rotated. By setting a ratio between the cycles of wheelhead movement and part rotation, polygons could be generated with any number of "sides" beginning with two, an oval shape.
The most commonly used shapes today have either three or four lobes, or sides. The three-lobed polygon can also be ground with a taper on the shaft and in the bore for an interlocking engagement. Three and four lobe forms can be press or sliding fits. Originally intended as a substitute for drive connection, using splines, keys, flats and serrations, polygons have now found their place in many other applications.

Our company is a contract shop providing the specialized grinding service. In the past years, few manufacturers had sufficient production to justify purchasing a Fortuna Polygon Grinder, although a number are being used proprietarily.
Polygon systems are also widely employed for repair of damaged drive connections. When costly shafts and hubs incorporating spline drive connections have failed through damage to the teeth, it is no longer necessary to totally replace them. This will also be discussed and illustrated later. Why, Where, And When To Use Polygons are not the answer to all problems. They provide optimum results but are not usually considered when less than optimum performance is satisfactory. Often, less costly methods will do. Generally, these are the reasons designers turn to polygons:

• To overcome the problems usually found with spline connections, such as failure caused by various torsional effects.
• To eliminate stress risers which cause part failure.
• To provide maximum concentricity and low clearance, when required on connections such as "floating shafts".
• To reduce backlash, which is near-zero with Polygon.
• To provide optimum control of angular positioning, especially on long shafts. Grinding after hardening provides for this. Typically, parts can be oriented within 2 seconds of arc over a 24" shaft length, essential in many cam and gear assemblies.
• To permit finish machining of high-torque parts after hardening. In all other methods, post-machining heating treating introduces various distortions in splined shafts.
• To reduce manufacturing costs on large volume production items, especially in the areas of inspection and straightening.