Four Bar Mechanism Release Latch

by LucidOne, published

Four Bar Mechanism Release Latch by LucidOne Dec 29, 2009

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Safety is job #1, quality is also job #1, as is innovation.

Sometimes you might be working on a project and need a way of releasing something heavy without the risk of it landing on you. This self-locking release latch can be attached to carabiners on both ends and released by pulling on a string or wire through the middle hole. If the material being held is the right size the latch will lock shut without a spring.
Due to the geometry the force needed to release the latch is pretty much independent of the load being held, this prevents the latch from jamming.

It was inspired by the sea catch release latch and Vise-Grips.

Always wear your safety glasses. Do not use for large loads without checking the material properties and calculating the maximum load. Always design with a reasonable factor of safety. Don't be dumb, be safe.



1) Make one of links zero and two. Make two of each of the rest.

2) Drill small holes out to 3mm

3) Use M3 nuts and bolts as pins, and use Loctite to keep the nuts from backing off. Rivets may also work well for these pins.

4) Add optional spring. Remove sharp edges, polish, etc.

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Beautiful! Really great job, thanks! Makes me really want a CNC mill.

It was originally designed as a catapult/trebuchet release mechanism so you can stand at a safe distance. This one was cut out of 6061-T6 aluminum with a Taig CNC mill but you could probably try making one with a 3D printer or a laser cutter. Obviously the strength depends on the materials, and aluminum really isn't the best choice since fatigue cracking will eventually cause a catastrophic failure with little to no warning.


This is beautiful, and my curiosity must know 1. what you are using it for and 2. how was this cut?