This video uses a high-speed camera to investigate the mechanics of various saws. The primary question explored is why saw blades with fewer teeth cut faster. The popular theory that the gullets (spaces between teeth) of high-tooth-count blades fill with sawdust is tested and conclusively debunked with high-speed footage. The actual reason, as far as the video can tell, is related to the energy required to sever wood fibers. A key insight is that the speed difference between high and low-tooth-count blades is dramatically more pronounced in rip cuts (along the grain) than in crosscuts (across the grain). This is because rip-cutting with many teeth repeatedly severs the same fiber bundles, wasting energy, while cross-cutting primarily involves separating fibers, which is less energy-intensive. The video also examines the distinct mechanics of rip saws, crosscut saws, chainsaws, bandsaws, and oscillating multi-tools, explaining concepts like rake angle, saw set, and chainsaw kickback.
An Analysis of Saw Mechanics with a High-Speed Camera
0:17 Fewer Teeth Cut Faster: An initial test with 24, 60, and 100-tooth table saw blades confirms that blades with fewer teeth cut significantly faster through oak, with the 100-tooth blade causing burning.
2:52 Gullet Theory Debunked: A common explanation is that the gullets on high-tooth-count blades fill with sawdust, impeding the cut. High-speed footage clearly shows the gullets are nowhere near full, invalidating this theory.
3:35 Rip vs. Crosscut Efficiency: The video presents its core finding: the performance gap between high and low-tooth-count blades is massive for rip cuts (along the grain) but minimal for crosscuts (across the grain). This is because rip-cutting involves severing tough wood fibers, and using more teeth means inefficiently re-cutting the same fiber bundles.
4:33 Rip Saw vs. Crosscut Saw Mechanics: Rip saw teeth act like chisels, chopping fibers. They are efficient along the grain but cause tear-out when crosscutting because they tear fibers apart. Crosscut saw teeth are angled to score the sides of the cut first, like knives, cleanly severing fibers before removing the waste.
6:04 Rake Angle: The aggressiveness of a saw tooth is determined by its rake angle. A high positive rake angle is aggressive and efficient but can grab. A negative rake angle is less aggressive, requires more power, but produces a cleaner finish and is used for hard materials.
7:52 Bandsaws and Chainsaws: The evolution from inefficient reciprocating saws to continuous-cutting bandsaws is shown. Chainsaws take this further by curving the blade in the direction of the cut.
9:15 Chainsaw Tooth Design: A chainsaw tooth combines a rip and crosscut chisel into one. A "raker" in front of each tooth acts as a depth gauge to control how much wood is removed, preventing the aggressive teeth from digging in too deeply.
10:13 The Cause of Kickback: Kickback occurs at the tip of the chainsaw bar where the curved path effectively moves the raker out of the way, allowing the teeth to take an uncontrolled, deep bite that throws the saw back at the operator.
11:32 Oscillating Multi-Tool: This tool is slow but uniquely useful for plunge cuts. It is also relatively safe on skin because its rapid side-to-side vibration tends to move soft, flexible materials with the blade rather than cutting them.
12:28 Saw Set: Saw teeth are bent slightly outward (the "set") to cut a kerf wider than the blade, preventing it from binding in the wood. On fine blades like hacksaws, a wave is pressed into the blade to achieve the same effect.