Secateurs

 Update from Alan

The fourth item to come out of last Saturday’s class was the unexpected result of the secateurs ‘prune off’ demonstration. For those who weren’t in the class, we tested how much force was needed to cut through a piece of dowelling using a range of secateurs. At one end of the range was a really cheap ‘no name’ tool that someone had thrown away in a bag of leaves. I’d picked up the bag at the side of the road and dumped the contents into my composter and, some years later, found the secateurs in an advanced state of corrosion. At the other end of the scale was an $80.00 tool, manufactured by Barco, which seems to be well regarded in the grape growing industry where pruning is an intensive year round activity. Examples from the ubiquitous Felco line, found at better garden suppliers, were also included.

This game has been played every year since the classes started in 2004 and the results have always been consistent. All the blades were razor sharp, as shown by their ability to cut a sheet of paper, but the more costly the tool the less effort it took to cut the standard dowel. Much the same result ensued on Saturday until Troy produced his Fiskars pruners. The ‘Power Gear’ model sliced through the dowel not quite like butter but clearly with less effort than the Barco pruners at three times the price. How come?

The selling ‘feature’ of the Power Gear is a rack-and-pinion arrangement which rotates the lower handle as the jaws are closed. I bought the model, disengaged the pinion and could detect no degradation in blade’s ability to cut the dowel. The ‘gear’ appears to be a marketing device used distinguish the design and to justify the $32.00 price tag.

Of the examples used, the Barco has a large head - it can cut up to 1.25 diameter if the wood is soft enough, the Felco has a medium head, and the Fiskars have a small head - up to maybe 0.75" dia capacity - but, as they were all cutting the same size stick, what has this got to do with the required force? Turns out, everything.

For a given size of stick, the bigger the blade is the greater the distance between the pivot and the ‘sweet spot’, the actual contact point of the cutting edge. For an 7/16 stick, the Fiskars distance is 1.1” for Barco 1.8”, a more than a 3:2 mechanical advantage in favour of the smaller head. In other words: the handles of the small bladed tool need only two thirds of the squeeze force of the larger bladed tool to exert the same cutting force on a given diameter of stick.

Price and ‘quality’ have nothing to do with how easily secateurs will cut a stick, simple geometry determines that. P & Q have to do with durability, functional design details, balance and what can be best described as ‘feel’. I have never seen this written down anywhere and, but for Troy giving me the gears, I’d likely never have given the matter any thought.

This is why I teach the classes. I learn stuff.

Glen said: This kind of information is exactly why the Peel Teaching Garden classes are so useful. It is unlikely a salesperson at Rona, Canadian Tire or Home Depot or even Humber Nurseries could give this kind of insight and guidance.