Salvaging Pitted Plane Irons

There’s no question that modern irons are far superior to the vintage irons that you find in virtually all old planes.  Unless you’re a casual   woodworker who only uses your plane(s) a few times a year, the investment in a new A2 or O1 steel iron (from companies like Hock, Veritas, or Lie Nielsen) will provide far superior performance.  These irons are thicker, flatter, and hold an edge better than the old tool steel irons.  That said, woodworkers 100 years ago did just fine with what they had, and many woodworkers today are also collectors and prefer to use their vintage tools in the same manner and with the same limitations as their ancestors.  Regardless of what camp you fall into, at some point, you’re going to come across a plane iron that is pitted.  It is inevitable and unavoidable.

Conventional wisdom and learned advice tells you to pass on irons that are pitted from rust damage.  True, there are plenty of vintage irons out in the market that are undamaged or in at least serviceable condition.  Many people, in fact, throw away or sell for scrap old damaged irons in lots on Ebay, and with good reason.

The problem is, of course, that pitting on the non-beveled (flat) side of the iron often prevents you from polishing it flat and smooth.  Pits that reach the cutting edge create tiny irregularities that subsequently reveal themselves in the shaved surface of your wood.  By contrast, pitting on the beveled side of the iron is of little consequence since it never actually touches the wood.  It might look bad, but it doesn’t affect the iron’s performance.  The only part of the iron that matters is the cutting edge, and both the bevel and flat side of that edge must be properly dressed – sharpened and honed to cut clean.

So what to do with irons that are badly pitted?  If the pitting is limited to the un-beveled side, all you might need do is flip it over, reversing the bevel direction.  Note that you’ll lose about a quarter inch of iron length making this reversal.  And if both sides of the iron are pitted, there is little point.  A better, and simpler solution, is to adjust your cutting angles slightly, adding a slight back bevel to the polished (un-beveled) side – enough to remove the pits and reach clean metal.

Using a standard bench plane as an example, the iron is seated on the frog at a 45 degree angle.  Most woodworkers sharpen the iron with an angle somewhere in the 25 to 35 degree range.  By putting a back bevel of a couple of degrees on the pitted back side, you effectively cut through the pitted surface creating a clean, undamaged edge.  Adjusting your primary bevel angle to compensate (if desired), you end up with a cutting angle of about 46 to 50 degrees – not a critical difference for many woodworkers.  In fact, increasing this angle of attack is advantageous when planning wood with difficult grain. [1]

Now, if you’re obsessive about your edge geometry and angle of cut, this might not be a satisfactory solution.  Although if that’s the case, you probably shouldn’t be futzing with a vintage plane in the first place, let alone salvaging a pitted plane iron.  But if you’re like me, having one or two extra irons set up for different purposes is a must, and finding good use for old irons suffering from age and neglect makes me feel good.  It’s just a matter of purposing them for the right job.

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[1] Hock, Ron, Back Bevels and Plane Geometry, 2010.