Taps Dies - Correct Speed

Several factors, singly or in combination, cause variations in the permissible speed for taps dies.

These include thread pitch, tap-chamfer length, percentage of full thread to be cut, tapped hole length, cutting fluid used, straight or tapered threads, machine tool used and workpiece material. Feedrate and spindle speed must work in tandem to tap threads accurately, and boosting spindle speed means that operators must change the feedrate accordingly. Rigid, or synchronized, tapping synchronizes feedrates with spindle speed via a feedback mechanism.

Of the many factors that affect self-reversing attachments on high-production applications, the correct speed for taps dies is perhaps the most critical.

Every tap manufacturer provides taps dies chart information with a recommended speed range for specific taps in specific materials. Machine operators must select the best speed within that range, which is not always the highest speed. All taps dies perform better and last longer if used at a specific speed.

Faster speeds shorten tap life, induce tap changes and reduce the holes-per-minute rate due to increased downtime. Spindle speed also affects the life of self-reversing taps dies attachments, which operate most effectively in the mid-range of their speed capability.

When using a self-reversing taps dies for cold-forming threads, acceptable torque output is limited by the size of the unit's components and is less than the output of the machine itself. Cold-form, or roll-form, tapping requires approximately 20 percent more torque than an equivalent cutting tap in the same workpiece material. Although the torque required increases as cold-form taps dull, they may produce acceptable threads even after doubling the required torque.

For maximum cold-form-tap life, a rigid tap driver and machine reversals are recommended. However, if the objective is reduced cycle time at the cost of more frequent changes, then self-reversing, constant-speed taps dies are the best choice.

With cold form tapping, material grain fibers are not cut as in conventional tapping. Pressure forms internal threads and grain fibers follow the contour of the thread. Cold-forming taps dies have neither flutes nor cutting edges and, therefore, produces no chips. Cold-forming taps dies work well for threading ductile materials such as low-carbon steels, leaded steels, austenitic stainless steels, aluminum die-casting alloys (low silicon), wrought aluminum alloys, zinc die-casting alloys, copper and copper alloys.

It is a good idea to start at speeds at the low end of a recommended speed range when cold forming threads using coolants without EP additives or if the lubrication quality of a coolant is unknown.

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