A cylinder escapement uses a hollow, partly cut-away cylinder on the balance arbor. Raised escape-wheel teeth enter its opening, stop against its inner surface, and leave on the return swing. Impulse is delivered at the two edges of the opening; outside and inside locking alternate.
Actuator selection checks for Cylinder Escapement Mechanism
When comparing cylinder escapement mechanism with an electric actuator, do not compare peak force alone. Installed length, speed under load, cycle rate, IP rating, and controller behavior often decide whether the change is practical.
With leverage, force is traded against travel. A bracket change that improves force can also increase required stroke, slow the output motion, or move the actuator into a poor mounting angle.
For moderate loads and defined stroke lengths, a packaged electric actuator can reduce system complexity. The tradeoff is that force, speed, and heat must be checked against the actuator data sheet rather than assumed from cylinder sizing habits.
- Compare continuous force, not only peak force, before considering an electric actuator.
- Check speed under load, duty cycle, and installed length against the original system.
- Confirm the environment, ingress rating, and control requirements are compatible.
For a FIRGELLI electric alternative, start by comparing the motion against the FIRGELLI electric linear actuators. The linear actuator replacement finder can help when the existing device has a readable model or part number, but final selection still requires a mounting and duty-cycle check.
Cylinder Escapement · Hollow Section and Timing
Follow a raised tooth through the hollow cylinder. Compare bore size, retained-wall area, beat rate and wheel speed.
Equation Used
- Bore is concentric with outside surface.
- Retained wall spans185° in this selected section.
- One tooth per full oscillation, two beats per oscillation.
- Triangle proportions and contact timing are explanatory selections.
- Raised tooth necks occupy a lower axial level.
The two impulses need not advance the wheel equally. Geometry is not a manufacturing prescription.
A tooth passes through the cylinder
Hiscox 1178 shows the slotted cylinder; 1179 illustrates the tooth entering its hollow side and acting at the section edge. The reconstruction makes that cut section visible, with a second enlarged view of the contact.
First, a tooth rests against the outside surface while the cylinder turns with the balance. As an edge reaches the tooth, the tooth advances across that edge and supplies an impulse. It then drops into the hollow and locks against the inside wall.
On the return swing, the opposite edge reaches the tooth. The tooth gives the second impulse while leaving the hollow. The following tooth then arrives at the outside surface. One complete oscillation includes these two impulses and advances the wheel by one tooth pitch.
The raised triangular heads occupy the contact plane. Their narrower supporting necks pass below the cylinder cutout. A plan section should therefore not be mistaken for a solid gear pushing through a solid shaft.
Compare section dimensions and timing
Change the outside diameter and wall thickness to see the bore and retained-wall area. Change tooth count and beat rate to compare wheel timing. The contact animation recalculates a selected tooth layout for those dimensions.
The page explains the mechanism and its counting relationships. It is not a tool for setting watch clearances, selecting material thickness for strength, or certifying a restoration. Actual tooth faces, cylinder lips, drop and lock depend on the particular movement.
Section area and tooth-count relationships
For outside diameter D and wall thickness t, bore diameter is d=D−2t. In the selected reconstruction, retained material spans 185°, so cross-sectional wall area is A=(185/360)π(D²−d²)/4. This is the area of the retained annular sector, not the strength or contact area.
The complementary open sector is 175°. These numbers describe a selected explanatory section; the old input called an angle above 180° the opening and converted it to a supposed lip margin. That margin was not a validated clearance and has been removed.
With B beats per hour, beat frequency is B/3600 and full oscillation frequency is B/7200. With one tooth per full oscillation and N teeth, wheel speed is B/(120N) rpm. Total wheel advance per full oscillation is 360/N degrees. The two individual advances need not be equal.
Selected contact geometry
The animation sets outer radius rₒ=D/2, inner radius rᵢ=rₒ−t, tooth pitch p=2π/N and wheel reference radius R=2.8rₒ/p. Relative to the cylinder centre, a locked tooth has vertices V=(−rₒ,0), A=(−rₒ−0.8rᵢ,−0.35rᵢ) and F=(−rₒ−0.72rᵢ,0.04rᵢ). They rotate rigidly about (0,R).
Circle intersections determine entry-end, inside-lock and exit-end wheel positions. During each impulse, the cylinder edge follows the angular boundary of the tooth within the annular wall. That boundary is found from tooth vertices and intersections of the triangle edges with the inner and outer circles; it follows the impulse face and then the trailing corner as it crosses the wall thickness. Free-swing and drop timing are selected for explanation. This preserves the shown contact points without claiming a production tooth profile, continuous dynamic torque model or interference certification.
0.8 mm cylinder and 15-tooth wheel
With outside diameter 0.8 mm and wall thickness 0.11 mm, the bore is 0.58 mm. The selected 185° retained wall has a section area of about 0.123 mm².
At 18,000 beats per hour, the balance makes 5 beats or 2.5 complete oscillations each second. A 15-tooth escape wheel advances 24° per complete oscillation and turns at 10 rpm. Changing cylinder dimensions does not change those counting relationships.
Interpret the section correctly
The cylinder itself provides the outside and inside locking surfaces. Its opening edges provide the impulses. This differs from a detent escapement with a separate locking lever and one impulse per complete oscillation.
The enlarged drawing is useful for following contact but does not specify working clearances, lubrication, wear, tooth bending strength or accuracy. The balance outline and hairspring identify the shared arbor; their motion is prescribed from the selected contact sequence.
Cylinder escapement questions
Is the cylinder solid?
No. The hollow and cut-away side allow a raised tooth head to enter and leave.
Does it give one or two impulses per full oscillation?
Two, one at each opening edge on opposite swings.
Why does the wheel pause twice?
The tooth locks first outside and then inside the cylinder before leaving.
Is the opening 185°?
In this reconstruction 185° is the retained wall; the opening is the complementary 175°.
Does a larger bore prove a better escapement?
No. It changes this selected geometry, but performance requires the actual tooth, drop, lock and movement dimensions.
References
Gardner D. Hiscox, Mechanical Movements, Powers, Devices and Appliances, no. 1178–1179, printed page 290: the hollow cylinder, cutout and edge impulse.
Mark V. Headrick, Clock and Watch Escapement Mechanics, chapter 18, and cylinder escapement animation, consulted for the raised triangular tooth and alternating contact sequence. The dimensions and tooth proportions used here are explicit independent explanatory selections.
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