For a frictionless linear slam-latch ramp at angle θ from the bolt axis, balancing selected spring force Fs requires ideal ramp-normal N = Fs/sinθ and a closing-direction component Fc = Fs/tanθ. These are force projections, not latch ratings.
Spring-Bolt Slam Latch
Explore frictionless straight-ramp force projection on an illustrative spring-loaded linear slam latch.
Equation Used
- Ramp is straight and θ is measured from the sliding bolt axis.
- Striker closing direction is perpendicular to the bolt axis.
- Selected spring force is constant and friction is zero.
- Installed geometry, impact, retention, strength, wear and ratings are excluded.
The selected gap is displayed separately; actual installation clearance and engagement require the complete latch and keeper dimensions.
Spring bolt, ramp and striker
The keeper approaches perpendicular to a spring-biased sliding bolt. Contact with the selected ramp pushes the bolt into its housing. After the keeper passes, the bolt extends and its flat underside retains the keeper. Pulling the blue release tab retracts the bolt before opening. The animation uses a straight relative path and illustrative dimensions; the calculator retains a constant ideal spring force.
What the calculator determines
Select ramp angle, ideal spring force and a gap ledger value. The calculator reports the frictionless closing-direction component, ideal ramp normal, ramp rise per 10 mm of run and the selected gap.
Frictionless straight-ramp projection
N = Fs/sinθ; Fc = Ncosθ = Fs/tanθ; rise per 10 mm run = 10tanθ.
Selected-input arithmetic
At θ = 35° and Fs = 5 lbf, the ideal closing-direction component is about 7.14 lbf and ramp normal is about 8.72 lbf.
Reference geometry only
Friction, spring travel and rate, striker shape, door trajectory, impact, tolerances, engagement depth, keeper geometry, release linkage, back-drive resistance, wear, strength and ratings are excluded. Gap is only a selected ledger value; no universal pass/fail window is asserted.
Questions
Is closing force the same as holding strength?
No. Holding depends on the retained face, keeper and complete structure after engagement.
Does the selected gap prove engagement?
No. Complete installed geometry and tolerances are required.
References & Further Reading
- Southco, Push to Close Latches, Sliding Flush Style, spring, sliding bolt and release arrangement. Wikipedia contributors. Latch. Wikipedia
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