Chris Schwarz's Blog

Corrugations: Stopping Stiction? Or For Suckers?

Handplanes with corrugated soles vex many woodworkers. If you find them on a vintage plane, should you grab it or should you shun it? If you order a bench plane from Lie-Nielsen Toolworks, should you spend the extra $35 to get a corrugated sole or is that money better spent on some Lehman Brothers stock?

Corrugated soles started showing up on planes in the late 19th century. Craftsmen noticed that their newfangled metal planes were harder to push than their old-fashioned wooden-bodied planes, according to period accounts and patent papers.

So manufacturers began to mill corrugations in the soles of their planes. For a peek at their reasoning, check out this 1869 patent by E.G. Storke:

“…¦(E)xcessive friction was caused by their exact and even faces (of their soles), which were not materially varied by use or atmospheric changes.

“When used on very level surfaces, there were so many points of contact that the friction was troublesome, and the adhesion was further increased by atmospheric pressure, as partial vacuums would thus be formed.”

In other words, the planes were sticking to the work when the boards became really flat. I’ve encountered this when working with closed-grain woods, especially poplar and maple. In fact, if the board isn’t too large, I can occasionally lift the board off the bench because it is stuck to the tool’s sole. It’s a neat trick.

But is the plane harder to push if it doesn’t have corrugations? Many pointy heads I’ve talked to about this are dubious. Friction, they explain, is a function of force , not the surface area of the sole.

I have planes with both smooth soles and corrugated ones, and if there is a difference in effort required to wield them, I cannot discern it.

But there are some practical differences you should be aware of:

1. Corrugated soles on vintage planes are easier to flatten because there is less metal to remove. So if you have an old sole that needs work, corrugations are a plus.

2. The corrugations hold paraffin or wax. This wax wears away completely during use, so I assume it is lubricating the sole.

3. Corrugations on some sizes of vintage tools are rare. So if you are a collector, keep an eye out for them.

So here’s my bottom line: Corrugations don’t change the function of the plane for better or for worse, so it doesn’t really matter either way. I wouldn’t spend extra money to have them added, but I wouldn’t kick them out of bed for eating crackers, either.

– Christopher Schwarz

11 thoughts on “Corrugations: Stopping Stiction? Or For Suckers?

  1. Malcolm

    The little comparisons I have made of corragated stanleys is that the castings are a bit thicker than the smooth counterparts of the same type. I am pretty sure weight savings was not the issue. In spite of several comments above, it is quite certain that one can develope a noticable vacuum between 2 well mated surfaces without heat or pumps. You can do it with 2 pieces of wood too which raises the question of how flat where the old timers wooden planes? Hmmm kinda leads back to the added friction due to added weight explanation. Or maybe the added volume of air in the grooves may be enough to reduce the effect.

    There is no doubt corregated planes are much easier to flatten! I have gone so far as to bore a nice pattern of shallow holes all over the bottom of a #5. It worked great and the tool looks very cool besides.

    Also consider the fact that the bottom of japanese planes are not flat by design. My next project will be to make a #4 have the ‘wave’ form.

    Ok enoughsenough Just don’t forget to turn off the computer and do some woodworking!

  2. Peter Khoury

    The point I was trying to make was that the evolution from wood- to metal- bodied planes was a double-whammy if you like:

    1. I assumed that a metal-bodied plane has a greater mass than the wood-bodied equivalent (I don’t know, since I’ve neither owned nor used a wood-bodied plane). It’s a fairly safe assumption to make though, since gray iron has a density of around 450 lbs per cubic ft, whilst woods range between 22 lbs per cubic ft (Northern White Cedar) and 51 lbs per cubic ft (Hickory) (Air dried specimens as per the US Dept of Agriculture)

    AND,

    2. The coefficient of friction of a metal-bodied plane can be expected to be higher than it’s wood-bodied equivalent.

    The reduction in mass resulting from the corrugations should be negligable – I wouldn’t expect a noticeable difference in ease of use based purely on the reduction in mass.

  3. Tom

    Chris,

    Peter’s point is that a metal plane could be harder to push even if it was the same weight as the wood one – it’s a function of the coefficient of friction as well as the weight.

    I’d expect that corrugations would indeed help with the perceived force required to use a plane. It has to do with the volume of air trapped between the plane and the workpiece compared with the distance that the plane needs to be lifted in order to break the suction. The rate at which you’re truing to move the plane is a factor as well.

    Remember the science demonstration in which you fill a glass with water, put a card on top of it and turn it upside down? If you try that with progressively larger amounts of air trapped in the glass, eventually you’ll get to a point in which the pressure differential won’t keep the card in place.

  4. Christopher Schwarz

    Peter,

    Well-put. There was more friction, but it was caused by the weight of the metal plane.

    The corrugations don’t remove enough weight to be noticeable in my book. I’m sure someone here could come up with the amount of weight actually removed by the corrugations.

    Chris

  5. Peter Khoury

    I’m going to take the "pointy head" approach here:
    Friction is indeed independant of area – indisputable fact.

    The frictional force to be overcome is dependant on the normal (perpendicular) force at the point of contact and the co-efficient of friction of the materials in contact with one another.

    It follows therefore that a heavier plane will have a greater frictional force to be overcome, since the normal force will increase as the mass of the plane increases.

    So, question time:
    If "…Craftsmen noticed that their newfangled metal planes were harder to push than their old-fashioned wooden-bodied planes…" is it safe to assume that the metal-bodied planes referred to were substantially heavier than the wooden bodied ones? If so, a proportionately higher frictional force would have to be overcome. The corrugations in the sole would obviously serve to reduce the overall mass of the plane, hence a proportionately lower frictional force to be overcome.

    The coefficient of friction (μ) for a wood-wood interface varies between 0,25 and 0,5; μ for an oak-cast iron interface is quoted at 0,49. If a favourable wood-wood (plane-workpiece) combination yielded a μ of say 0.25, it follows that the modern day metal-wood combination would result in double the friction force.

  6. Carl Stammerjohn

    One process where a corrugated plane is not desired is when shooting veneer edges. You can’t shoot just one piece of veneer – it’s too flexible – but if you were to shoot three or four pieces, the corrugated bottom could keep you from getting a straight edge. More pieces than that would not be a problem, as they would be thicker than the width of the corrugations.

  7. Christopher Schwarz

    Phil,

    Dropping any plane made from gray iron can break it. I’ve seen some sad cases out there — both corrugated and not.

    I suspect that anytime you remove metal from a critical surface (such as the sole) you are weakening it. However, I suspect that it’s not enough of a problem to be a major defect — otherwise we wouldn’t have so many 100-year-old planes with corrugations to ponder.

    Chris

  8. Phil

    Really well written and thought out. One more factor I wonder about though. I was very sad when a plane handed down from my great grandfather was dropped and broke right in the center. It was corrugated. It begs the question: does the corrutation also weaken the plane?

    I’m quite sure I’ve never planed a board flat enough to make it stick. Maybe someday.

  9. Luke Townsley

    Part of this whole discussion may have to do with the way that plane soles were lubricated in the 19th century.

    A heavy wax like beeswax or even tallow, while it will work into wood, won’t do exactly the same with iron. I suspect that some didn’t use anything to lubricate the soles.

    It may have been the wax itself that was sticking instead of suction. (If it was suction, why didn’t it also stick with a wood plane almost as bad?) In the case of a corrugated plane, less surfaced waxed and more pressure on that surface to work in the wax would probably have helped some woodworkers.

  10. James Watriss

    I think suction also requires perfectly mating surfaces, though, and a source of suction. So maybe if you had a REALLY well tuned No. Xc plane, that was mirror flat, and you planed with it until it heated up, and you left it on some very flat wood, and it cooled down sufficiently to make a vacuum…

    I dunno. My favorite, regular "go-to" plane is an old sweetheart 3c, stamped "imperfect." I can’t say one way or another that the corrugations contribute, or don’t, to the plane’s handling.

    I do think it’s kinda noticeable on a bronze plane, which doesn’t soak up as much oil or wax as a more porous iron plane. That could just be me, though. A York pitch 4c is expensive enough, I may be trying to feel that the corrugations actually do something.

    On the other hand, the bit about removing more metal is worth noting. I have an old 5 1/2 that was so bowed when I started flattening it that there’s now a visible tapered shape to the corrugations in the sole. Had it been a fully flat sole, I’m sure it would have been even more work. The corrugations also gave the swarf a place to go, (visbile when lifting the plane) which might have actually helped keep the abrasive to iron contact.

  11. Mattias in Durham, NC

    Common sense (which I concede is not always correct) would dictate that vacuum *does* add to friction. Take a suction cup, for instance. It is impossible to pull straight out but also hard to slide sideways.

    Common sense would also dictate that in order to release vacuum, grooves would have to extend to the edge, or you also need air holes. Maybe the grooves only work if the work piece is flat enough that the perfectly flat parts are smaller than the longest groove. Just some thoughts on this, and if you have a plane to destroy you can drill some holes through its sole to test my theory.

    On a side note, I was curious when Glen Huey tested the Jet combination planer/jointer which has grooves. He said "we felt it added a bit of drag to the workpiece." Huh? Can you verify this? Grooves in modern day machinery are worse than a flat surface?

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