## Hand Tools Archive

Subject:
Re: Center of effort?
Response To:

Derek Cohen (in Perth, Australia)

Having read through this series of articles and your previous article devoted to "Center of effort", I can't understand what you mean by the term. It seems like it could be the angle off horizontal of the line formed between the users rear hand and the tip of the blade. But, if so, I fail to see how there could be a difference in value between for example a BU and BD smoother if both are cast iron and have the same handle and similar handle position. I do understand that those two planes would have different centers of gravity.

Hi Lars

In a nutshell, "centre of gravity" refers to where the stability lies, for example, a low centre of gravity would see the weigh distributed low down. "Centre of effort", on the other hand, involves a movable centre of gravity, that is, we can direct where the centre of gravity will be. This can be low down or raised up high. When low down, we create stability (and power); when high up, we create instability (and an inefficient use of power).

Using our arm/hand, we create a force vector. In this instance the design of the handle, and where we direct force on the handle, will determine this vector.

Stanley planes create a higher centre of gravity by raising the blade up high on a vertical frog. One of the design factors for the custom planes that I did not mention in the article (as there was already too much info), was the construction of the body. What Lee Valley did was lower the centre of gravity on the custom planes with a convex floor, that is, adding extra mass along the length of the centre of the body. The blade is also shorter and its centre of gravity is also distributed lower. The BD Custom Plane still has a higher centre of gravity than the BU range, where the bed and blade is placed low on the body.

This combined lowered gravity along with the lowered centre of effort from vector on the handle design combine to create a different feel to a Stanley plane.

I found it interesting and ironic when Chris Schwarz posted on his blog his observation about the replacement Stanley handle (made by Bill Rittner) for his Lee Valley LA Jack: "I bought one of the first sets he made in cherry and put it on my Veritas jack yesterday. It dramatically changes the way the plane feels (and looks). With Rittner’s tote installed, it feels like I’m holding a Lie-Nielsen No. 62 that has a lot more mass.". What I have been emphasising is that one can help the Stanley/LN planes to feel more like Lee Valley by changing the handle to encourage a different vector.

Regards from Perth

Derek