## Hand Tools Archive

Subject:
Re: Center of effort?
Response To:

Lars Parrington
Derek, thanks for your response. Unfortunately, it didn't clarify things for me very much, if at all.

What I'm gathering from your response is that the "center of effort" could be defined as the height at which the user applies a horizontal force to the plane in order to move it forward along the workpiece. It seems self evident that this height would be best measured relative to the sole of the plane.

Consider a diagram of the forces acting upon a hand plane in the middle of a long stroke. Here the plane is being pushed at constant speed and so the forces are in equilibrium. It would show forces exerted by the user through both hands (each with both horizontal and vertical components). It would also show normal and frictional forces exerted by the workpiece upon the sole of the plane, as well as a force upon the cutting edge. Additionally, it would show the force of gravity, with an downwards arrow pointing to (or from) the plane's center of gravity (CG).

In the above case (and assuming the plane is being used on a level surface), the height of the plane's CG is irrevelant. However, if the plane were being accelerated (or decellerated), then an inertial force could be added to the diagram, which would act horizontally upon the plane's CG. During a very vigorous planing stroke, the height of that inertial force might begin to significantly affect how the plane moves, especially if the height of the CG is quite different from the height at which the user is pushing on the plane.

This is the only way I can see to relate the above definition of "center of effort" to both CG of the plane and to the "feel" of the plane. But it seems like a tenuous relationship at best, as it requires a highly energetic stroke and a large discrepancy between the heights of the CG and CE. So, I doubt this is what you are referring to by "center of effort".