For an ideal eccentric pin with offset e rotating from its zero-draw position, axial draw is δ = e(1 − cos θ). A selected weatherstrip thickness t and compression C require δ = tC/100, so θ = acos(1 − δ/e) when 0 ≤ δ ≤ 2e.
Ideal Eccentric-Cam Draw Model
Explore ideal eccentric-cam draw for a selected seal-compression target.
Equation Used
- The cam pin is a rigid point at fixed eccentricity e.
- The keeper slot permits transverse motion and transmits only axial draw.
- Seal compression is uniform and equals selected draw divided by initial thickness.
- Contact stress, friction, fasteners, wear, strength and security are excluded.
This calculator does not predict holding capacity or security performance.
Connected eccentric pin and keeper slot
The animation shows an eccentric pin fixed to a rotating cam hub and constrained in a transverse keeper slot. Rotation changes the pin's axial coordinate and draws the two normalized sash rails together against the selected seal.
This is an ideal kinematic cross-section. It does not establish the geometry of a particular commercial sash lock, contact stress, friction, security or holding capacity.
What the calculator determines
Select rail thickness, seal thickness, target compression and cam offset. The calculator returns required seal draw, ideal cam angle, selected compression and remaining geometric draw range before the 2e limit.
Rail thickness affects the illustration envelope only. No strength, screw pullout, security, durability or product fit is calculated.
Ideal eccentric displacement
δ = tC/100 and δ = e(1 − cos θ), giving θ = acos(1 − δ/e). The ideal eccentric range is 0 to 2e, so remaining range is max(0, 2e − δ).
Selected-input example
For t = 3 mm, C = 40% and e = 3 mm, required draw is 1.2 mm and the ideal cam angle is about 53.1°. Remaining geometric range is 4.8 mm.
Scope and correction boundary
The former page's fabricated hold-capacity equation and unsupported security, heritage, product, material, tolerance, failure and maintenance claims are removed, along with the fabricated restoration example and unrelated video.
Real hardware selection requires manufacturer dimensions, keeper engagement, fasteners, frame condition, contact loads, wear and applicable security requirements.
Questions
Does the model predict holding force?
No. The former fabricated capacity output has been removed.
Why is maximum draw 2e?
The axial coordinate of an ideal eccentric point ranges across twice its offset.
Does rail thickness change the cam equation?
No. It changes the illustrated rail envelope, not the ideal displacement identity.
Can this select a lock?
No. Product dimensions, engagement, fasteners, loads and security testing are outside scope.
Technical references
- NIST Special Publication 811 — SI units and coherent quantity notation.
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