Corrugated Planes are Groovy, Baby!

Stanley Bedrock no. 607C, c. 1911

Let me just put it out there right up front – I like corrugated planes.  Sure, their practical value is questionable.  I don’t care.  I like them, and all of the bench planes I use, as well as most of those in my humble collection, have corrugated soles.

Corrugations are a series of grooves milled into the sole of the plane.  Running front to back and spaced about 1/8″ apart, they stop short of the mouth at both the front and rear sections.  Introduced to the Stanley line of bench planes in 1898, corrugations were available on all sizes from the no. 2 through the no. 8, as well as the comparable sizes in the Bedrock series.  The no. 1 was never offered with a corrugated sole, and the no. 5-1/4 wasn’t introduced until 1921.  All the others, however, were available with corrugations and were distinguished from the plain versions by the suffix ‘C’ appended to the model number – nos. 2C, 3C, 4C, etc.  All the corrugated models were sporadically discontinued between the mid 1940s and mid 1960s.

While some argue that the feature was more a competitive marketing vehicle than a functional improvement, Stanley offered no explanation in its 1898 brochure, only stating “corrugated bottoms furnished without additional expense if so ordered.”  The reasoning most frequently accepted has to do with the vacuum created between two flat surfaces in contact with each other.  I’m no physicist, but I do know a little about science.  While this phenomenon is easily demonstrated with two sheets of glass, I have a hard time believing that wood is capable of creating much of a vacuum when in contact with something as small as the sole of a plane, even the large ones.

In my opinion, the reason why corrugations might work in theory is a simple matter of reduced friction.  Friction is defined as the resistance an object encounters in moving against another object.   Imagine that you are trying to push a plane across a board. If you apply a very small force, the plane will not move.  The frictional force between the two surfaces is greater than the force with which you are pushing the plane.  If the frictional force was less than the force you exert, the plane would slide forward.   So, in order to move the plane, you can do one of two things – reduce the frictional force of the plane against the board on which it sits, or push harder.

By milling grooves into the sole of the plane, Stanley reduced the amount of surface area that contacts the wood, the effect of which was to reduce the coefficient of friction between the two surfaces.  In theory, this should make a corrugated plane easier to push forward than one with a smooth sole.  This makes more sense to me than the theory of a vacuum created between the two surfaces, but I’m sure some will disagree.

Whether or not using a plane with a corrugated bottom provides a noticeably different experience to the average woodworker is debatable, but the idea clearly gained traction (no pun intended).  While less common than their flat soled brethren, corrugated versions were successfully sold for well over a half a century, and are still offered by some modern manufacturers today.

So here’s to corrugated planes… Easier to push or not, they’re groovy, baby!  Yeah!