The 30 basalt (A), chert (B) and quartzite (C) stone flakes used in the experiment. Here, each has been secured to the wooden blocks used to fix them to the upper arm of the Instron device. Flakes with a cutting edge that is not perpendicular to the length of wood (and therefore the ‘standard’ motion of cutting) had the block turned in the Intron's grip such that cutting edges were always straight when cutting the tubing.