A collapsing tap retracts its thread-cutting chasers into the head after the thread is completed. The smaller cutting envelope then allows straight withdrawal without unscrewing the tap along the finished thread. The calculator estimates the reverse turns and gross reverse time that this operation can avoid.
Collapsing Tap Interactive Calculator
Estimate the reverse-threading turns and gross reverse time avoided by a collapsing tap. Enter threaded travel, threads per inch, the comparison reverse speed and parts per shift. Actual net savings also depend on collapse, straight withdrawal and reset times.
Equation Used
- Single-start thread: one revolution advances one pitch.
- Entered axial travel excludes unspecified approach/runout allowances.
- Comparison reverse speed is constant; acceleration is omitted.
- Net savings require additional collapse, withdrawal and reset timings.
Illustrative straight-thread tap with stationary tool and rotating workpiece. Side section and end view show chaser retraction before withdrawal. Internal trip/reset mechanism is omitted because its construction varies by tap model. Stage timing is illustrative; entered reverse rpm is used only in the comparison calculation.
Cut, collapse, withdraw and reset
The illustrated arrangement holds the tap against rotation while the workpiece turns. This is one of the stationary and revolving arrangements described in the Landis tap literature. During the cutting stage, axial advance follows the thread lead.
At the end of the thread, the chasers move inward before the tap is withdrawn. The end view makes this reduction in cutting envelope visible. The tool resets only after it is clear of the bore. The displayed stage durations are illustrative, and the workpiece is replaced for the next demonstration cycle.
Actual taps use model-specific trip and reset arrangements. Landis describes yoke, trip-ring and lever options. The internal trip and reset parts are not shown; their construction depends on the selected tap. The tap head, radial chasers, shank and workpiece are shown schematically in section.
Where collapsible taps are useful
They can remove a reverse-threading operation in production internal threading where the tool size, thread form and machine arrangement suit a collapsible head. The manufacturer’s range includes straight-thread and receding-chaser taper-thread models; this animation illustrates a straight-thread sequence.
Cutting speed, feed, allowable thread depth and tooling selection depend on the material, thread and selected tap. Use the selected tap manufacturer’s data to choose cutting conditions; the reverse-time comparison does not determine a cutting-speed setting.
Reverse turns and gross time
A single-start thread with n threads per inch advances 1/n inch per revolution. Over entered threaded travel L inches, a conventional reverse withdrawal requires L × n revolutions.
At constant reverse speed N rpm, the corresponding gross time is 60Ln/N seconds per part. Multiplying by parts per shift and dividing by 60 gives gross minutes per shift. Reverse revolutions per shift equal Ln times the number of parts.
Net savings must compare complete machine cycles. Collapse time, direct withdrawal, reset and acceleration are not entered here. Additional approach or runout travel should be included only when it belongs in the comparison being made.
Worked reverse-time comparison
For 2.5 inches of threaded travel at 7 TPI, conventional reverse withdrawal requires 17.5 revolutions. At 400 rpm this takes 2.625 seconds per part.
For 240 parts, that represents 10.5 minutes and 4,200 reverse revolutions. These are gross reverse-operation quantities. Actual net time saved is smaller when the replacement collapse, withdrawal and reset operations take additional time.
Interpret the result as an operation comparison
Longer threaded travel or finer pitch increases the reverse turns. Higher comparison reverse rpm reduces the calculated time. Parts per shift scales the batch totals. The reverse-rpm slider does not control the cutting speed in the illustrative animation.
The tool still has to cut the thread, clear its chasers and leave the work. This calculator does not select cutting speed, determine thread accuracy or replace the selected tool’s operating instructions.
Collapsing-tap questions
Does a collapsing tap expand to release an internal thread?
No. Its chasers retract inward into the head so they clear the internal thread before straight withdrawal.
Must the tap rotate?
Not necessarily. Manufacturer literature describes both rotating taps and stationary taps cutting a rotating workpiece. The animation shows the latter.
Is the reported time the net saving per part?
No. It is the gross reverse-threading time removed from the comparison. Collapse, withdrawal and reset time must also be considered.
Why does reverse rpm not set animation cutting speed?
It describes the conventional reverse-withdrawal comparison. Cutting rpm is not an input, so the demonstration uses illustrative stage timing.
Does every tap use the same trigger mechanism?
No. Trip and reset arrangements vary by model and application. The drawing shows inward chaser motion; the internal trip and reset parts are not shown.
Manufacturer and historical references
- Landis Taps brochure, general-information pages 2–3: chasers, tap heads, stationary/revolving applications and trip/reset options.
- Landis Collapsible and Solid Adjustable Taps: inward chaser collapse and direct withdrawal.
- US1200181A, Collapsing tap and similar tool: one historical construction; its internal details are not treated as universal.
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