Tools & Craft # 96: Plumier, Crankshaft Design, And How We Waste Time at TFWW

I got called to the back of the shop a few days ago where some of my colleagues were having a heated discussion about crankshafts. They were perusing a copy of Charles Plumier’s 1701 L’Art De Tourner, Ou De Faire En Perfection Toutes Sortes d’Ouvrages Au Tour and one wag noticed that all the crankshafts in the pictures weren’t connected to either a flywheel or a screw by a straight rod, like in a steam engine, but a “U” shaped arm instead. The question that they were asking me was why, I had no idea, and we spent most of the afternoon tossing theories around and making cryptic drawings on the whiteboard to explain what we were talking about.

The following theories were proposed:

– It looks more elegant – maybe.

– It makes for a stronger casting – not in 1703 – the arms were forged – “S” casting spokes came later.

– It was easier to turn because the U protected your arm – maybe but isn’t a wood disk easier to make and cheaper?

– The spring action made the handle more forgiving – I’ll buy that.

– The spring action in the “U” shape acts like a mini transmission making for smoother and easier starts and stops and in the case of a screw allows for smoother action if there are variable amounts of resistance when turning the screw. This is the reason I like the best – solid engineering.

Tim said it best, “It’s a sweeter action,” and he’s right. That a vast number of foot and hand powered crankshafts are shaped this way means that the “U” design was an accepted standard form of construction. Individual craftsman might not have understood the engineering of springs and inertia, or the nuances of ergonomics, but taken as a package, as a group, the design must have been thought “sweeter” or they would have not wasted the extra material.

I am not aware of any historical information on why cranks should look like this, but I haven’t looked yet either – it might be out there staring me in the face. I am curious if you can think of any other reasons to make a crankshaft in this form, or if you know of any documentation. But for now at least – fun is over – it’s time to get back to work.


This “Tools & Craft” section is provided courtesy of Joel Moskowitz, founder of Tools for Working Wood, the Brooklyn-based catalog retailer of everything from hand tools to Festool; check out their online shop here. Joel also founded Gramercy Tools, the award-winning boutique manufacturer of hand tools made the old-fashioned way: Built to work and built to last.