## Hand Tools Archive

Subject:
Friction, and more
Response To:

Bill Tindall, E.Tn.
When I made some wooden planes I was struck by how effortlessly they slid across a wood surface. If they required the same lack of skill to adjust them I would still be using them.

The coefficient of friction of wood on wood is a piddly 0.2, about third that of steel on wood. The resistive force of friction is the object's mass times the coefficient of friction. One can see that a steel plane weighing times more than a wooden plane will be many times harder to push across a wood surface, considering only the resistance of friction and not the additional force to create a shaving. So, both weight and coefficient of friction conspire to make a wooden plane the more effortless choice when considering pushing or pulling it.

The force difference when lifting is obvious.

I was initially drawn to a heavy plane because it held in the cut better. Mr. Weaver taught me that a properly sharp blade will hold in the wood without the benefit of the plane's mass. I confirm this wisdom every time I plane something and when this situation begins to fail it is time to sharpen. So, there is no practical benefit of more mass for this aspect of planing.

Momentum is proportional to mass. More momentum could be beneficial if there was a case where the resistive force changed abruptly during the planing stroke, like hitting a knot or grain reversal. In this situation a heavy plane would be smoother to push.