TECH TIP #102; THREADING; TAP HOLDERS:

Selecting the right tap holder depends upon the equipment to be used for tapping. Machines not capable of accurately feeding a tap through the entire feed/retract cycle, including hand feed, cam, gear, hydraulic or air tappers, or conventional drill/mill/turn CNC machine, should use axial float holders. The most common have both tension and compression float that allow the tap to compress within the holder or pull out to allow the tap to follow its own lead to compensate for the feed errors in the machine.
If the hole in the part has been cast, punched or drilled in another machine or station, radial float holders are recommended. Radial float holders allow the tap to move off-axis while maintaining parallelism to the spindle axis. Holders are available that combine axial and radial float to provide both axial and radial movement of the tool.
If tapping is performed on lead screw tappers or machines that have synchronous or rigid tapping capability, the feed in these types of machines is far more accurate, allowing the use of solid holders. This would include collet, shrink fit, or hydraulic holders. Collets should be selected that are specifically designed for taps.
The newest holders are a floating type specifically designed for rigid or synchronous type machines. They provide approximately .015” of minimal float to compensate for slight errors that exist within any synchronized system. This slight movement compensates for any possible feed errors in the machine or lead error on the tap, to insure the tap operates to peak efficiency.
Self-Reversing holders do not require the spindle to reverse to retract the tap from the hole. They are used when the spindle cannot reverse or to prevent wear and tear from the constant cycling for those that do. They also allow higher tapping speeds for smaller diameter taps, where the recommended RPM may exceed the tapping speed of the spindle. In this case, since the spindle is not reversing, the full speed available for drilling can be used for tapping. Dave Miskinis, Sr. Technical Specialist Thanks and a gift to Ron Christiaens in British Columbia for suggesting we write about this topic!