Design for manufacture
6 min read
Snap-fits that still click after a thousand cycles
The cantilever snap is the cheapest fastener there is, as long as you respect the strain limit of the plastic.
Author
Tomás Reyes
Role
Mechanical lead
Published
Reading
6 min read
Strain is the number to watch
A snap-fit works by bending a small beam and letting it spring back. If the beam bends too far, the plastic yields and the snap loses its grip: sometimes on the first assembly, more often after a few dozen openings.
The simple beam formula gives the strain at the root from the deflection, the thickness and the length. We keep it below the limit the material supplier publishes, with margin for colour additives and moulding stress.
Geometry that helps
Taper the beam so strain spreads along its length
Add a generous radius at the root
Use a lead-in of about 30° for assembly
Choose the retention angle for how often it opens
Prove it on the bench
Calculations get us close; cycling tells the truth. We print or machine a set of snaps, open and close them a few hundred times on a simple fixture, and measure the retention force at the end. Only then does the geometry go into the tool.
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