Multiple Spindle Heads for Use with Different Pitch Taps

At times, tapping a pattern that has more than one pitch is required.  An example is a square four bolt pattern that has two holes to be tapped 1/4-20 and two holes to be tapped 3/8-16.  If a standard multi-spindle head that has all the output spindle turning at the same speed is applied, the 1/4-20 tap will feed at .050"/revolution and the 3/8-16 tap will feed at .0625"/revolution.  The result will be tap breakage ever time.  Solutions to this feed imbalance are available.

For our example problem, a solution is available.  The internal gearing will be adjusted to set the RPM of the 1/4-20 tap spindles at 1.25 times the speed of the 3/8-16 spindles.  This gearing will allow the 20-pitch tap to feed at .050" x 1.25 or .0625" for every revolution of the 16-pitch tap's spindles.  This keeps the feeds equal and eliminates the tap breakage.

For minor differences in pitch there may not be exact gear ratios to solve the problem.  An example is when a metric pitch of 1.25, which in our common inch system has a feed of .0492125"/revolution has to be mated with a 20 pitch tap.  The difference in pitch is less than 2 percent.  For this type of problem, there are available floating tap collets that have axial float built into the collet.  Depending on the depth required, these may be a solution for the problem.

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