A reverse-groove cylinder reciprocator guides a follower along opposite-hand helical groove reaches. At each end, a turnaround region transfers the follower to the other reach so continuous cylinder rotation produces alternating axial travel.
Reverse-thread Cylinder Reciprocator Interactive Calculator
Enter groove pitch, shaft speed and stroke to calculate ideal axial speed and travel time. The drawing illustrates back-and-forth travel; end-transition time is excluded.
Equation Used
- Opposite-hand straight reaches have equal constant axial pitch.
- Stroke is the axial distance traveled in one direction.
- Finite turnaround time and acceleration are excluded.
- Pin diameter is a drawing parameter, not a crossover design rule.
The companion view shows the same schematic and current inputs. Groove lines stay stationary; the moving marker illustrates axial travel.
How the reciprocator works
A rotating cylinder has right-hand and left-hand helical grooves. A guided follower travels along one groove, then transfers to the opposite-hand groove to return. The cylinder keeps turning in one direction while the follower moves back and forth along its axis.
On a constant-pitch reach, each revolution moves the follower axially by the pitch. The follower needs guidance where grooves cross and where travel reverses. The patent examples below describe different ways to control those transfers; the appropriate geometry depends on the particular mechanism.
Comparing traverse motion
Traverse mechanisms move a guide or carriage back and forth while the drive keeps rotating. Use the calculator to compare pitch, rpm and travel distance before considering a particular groove and follower arrangement.
Doubling pitch or rpm doubles ideal axial speed. Doubling stroke doubles one-way time and halves the full-cycle rate. Follower diameter changes only its displayed value and symbol, not the timing equations.
Ideal straight-reach relationships
For axial pitch P in millimeters per revolution and shaft speed N in revolutions per minute, ideal straight-reach speed is v = PN/60. For stroke L, ideal one-way time is L/v and ideal full-cycle rate is PN/(2L).
These relationships exclude the finite transition time and motion law of a real end turnaround.
Worked example
At 25 mm/rev and 60 rpm, ideal axial speed is 25 mm/s. A 75 mm stroke takes 3 seconds one way and gives 10 full cycles per minute when end-transition time is excluded. The 3 mm follower diameter is displayed separately and does not enter those calculations.
Reading the drawing and results
The numeric results assume constant-pitch travel with instantaneous reversal. A real follower must slow and change direction at each end, so its turnaround profile affects timing and acceleration. Pin diameter alone cannot determine that profile or a universal minimum crossover radius.
The drawing is a schematic of axial travel. Its groove lines remain stationary and its marker reverses immediately; it does not show cylinder rotation or physically resolved contact through crossings and end turns. Groove count and follower size are limited for display, and playback timing is adjusted for viewing.
The calculator does not determine groove depth, clearances, contact forces, stress, wear or service life. Those depend on the full groove profile, follower construction, materials, lubrication and operating load.
Reciprocator questions
Does the cylinder reverse rotation?
No. The follower changes between opposite-hand grooves while the cylinder continues rotating in one direction.
Is follower speed constant through the turnaround?
No. A physical follower must slow, reverse direction and accelerate again. These calculations cover constant-pitch travel and omit the time needed for those end transitions.
What does follower diameter change?
It changes the displayed diameter value and the size of the follower symbol, within display limits. It does not affect the speed or timing calculations and cannot determine a crossover radius by itself.
Does the animation show the actual groove contact?
No. It is a schematic of back-and-forth travel over stationary groove lines. It does not depict cylinder rotation, intersection guidance or a physically continuous path through the end turns. Playback timing is adjusted for viewing; use the numeric results for ideal travel time.
Primary references
- US4592244A, Device for reciprocally driving a shaft — continuous annular guide groove, intersection and follower guidance.
- US4914967A, Crossover mechanism for guiding a cam follower — right- and left-hand track portions and active intersection guidance.
- US4343200A, Reversing attachment for diamond thread screw — transfer between oppositely directed grooves without reversing screw rotation.
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