SNG 1: SOG PowerLock Multitool

SOG PowerLock Multitool (Photo by Shien Yang Lee, CC-BY-SA 4.0)

The star of this week’s Seek and Geek is a multitool I own. It uses a patented configuration of levers to achieve greater mechanical advantage. Compared to conventional pliers, which are made up of two class 1 levers pivoting about the same point, the handles of this tool pivot about a pair of pins (with formed heads) attached to the horizontal link in the image and attach to the jaws via the partially obscured button head socket cap screws.

Sprockets (Photo by Shien Yang Lee, CC-BY-SA 4.0)

As a 5-bar linkage, this mechanism should have 2 degrees of freedom according to Gruebler’s Equation. But the designers have incorporated a pair or sprockets that couples the motion of the handles, thereby eliminating one degree of freedom. I think this is to maintain the familiar usage pattern that people have come to associate with pliers and to facilitate the relatively fine manipulation of small parts that needlenose pliers often get used for.

I have noticed a couple of issues from using this tool. The greater mechanical advantage obviously comes with the side effect of requiring larger hand movements to move the jaws by a given amount. “Twice the cutting and gripping force” sounds great — it was partially why I bought it in the first place — but I have since come to realize that the limiting factor with using pliers is usually not how hard you can squeeze but how far you can open the jaws with one hand.

Another annoyance is the backlash introduced by the additional joints between handles and jaws. Normal pliers, even ones with worn pivots, primarily have out-of-plane free play. These have noticeable backlash around the actuation axis, which can be frustrating when trying to fine-tune gripping force on compliant or fragile parts.

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