A recent discussion over at the Rennaisance Woodworker got me thinking about the amount of camber I put in my plane irons. Those of us familiar with hand planes and planing typically understand each other when we say that our fore or jack plane iron has “significant” camber or that our try plane has “moderate” camber or that our smoother has “just a hint” of camber. But these terms are mostly subjective and to someone new to using hand planes, “significant”, “moderate” or “just a hint” doesn’t necessarily translate well. So although I don’t typically measure the amount of camber I put in my plane irons, I decided to try to quantitate it in order to better qualify the meanings of “significant”, “moderate” and “just a hint.”
So these are the three planes I am going to talk about in order of most amount camber to least amount of camber. The fore plane in front (also called a jack plane) has what I consider “significant” camber. In the middle, my try plane (also called a jointer) has “moderate” camber. Finally, in the rear, [one of] my smoothers have “just a hint” of camber. I took all the irons out since they needed honing anyway and tried to quantitate their amount of camber.
So after some trial and error using a piece of string, a magic marker and my awl, I got a close estimate of the amount of camber in two of the three irons (no matter how much I tried, I couldn’t quantitate the camber in the smoother, the radius was just way too big).
In hind sight, this would be a good way to mark your irons in order to grind a specified amount of camber. Simply use a dark colored permanent marker (I used black) to color the edge of the flat face of the iron. If you have it, machinist layout fluid would work as well, but it’s not necessary, the marker works just fine and is a lot less messy. Tie a small loop in the end of a long length of string. Place an awl in the loop, hold the opposite end of the string to the bench top a distance equal to the camber radius away from the edge of the iron and scribe the camber radius through the marker onto the iron. Then simply grind to this line and hone as demonstrated in Episode # 6 of the podcast.
So here are the results. They are in the same order as the planes above and you can see the resulting radii from my crude measurements. The radius of the fore plane (on the bottom) measured at about 10″. You can easily see the radius ground into this iron. The radius of the try plane was about twice the fore plane at about 20″ (middle). You can also easily see the radius in this edge, though it is not as distinct as the fore plane. Finally, at the top is the smoother. This iron basically looks straight, however, if you place a straight edge up to the edge, you will see a hint of light at each of the corners. The relief is definately less than 1/32″ but I couldn’t measure it.
When it comes to establishing the cambers, I grind the camber into the fore plane and try plane irons. However, when I grind the smooth plane, I grind the edge straight. Then, when I get to the honing, I simply do some extra honing of the outside corners in order to relieve them below the center ever so slightly. Again, the iron still appears straight, it’s only when a known straightedge is shown to the iron that you can notice the slight relief at the corners.
Here’s the finished result. This is a picture of the fore plane after the freshly ground and honed iron has been put back in and the depth of cut set. You can see the effect that the camber has. The center of the iron will take a relatively heavy cut (maybe between 1/32″ and 1/16″ thick) but the corners won’t dig in and leave tracks behind. You can see how this makes the plane capable of removing stock in a real hurry (about 1/4″ in about 8 strokes). No fluffy shavings here. They’re more like chips.
Similarly, the try plane will not leave tracks behind due to its camber. The camber is less than the fore plane’s by about half so the shaving thickness is similarly about half that of the fore plane. Again, these shavings aren’t fluffy. They’re thick enough to bring a board face true in fairly short order, but they are still thin enough to remove the scallops left by the fore plane and prepare the surface for final smoothing. The camber in this plane also helps in squaring edges by enabling the plane to take a wedge shaped shaving just by shifting the position of the plane on the board’s edge.
I didn’t take any pictures of the smoother as you really can’t see the iron above the sole like you can with the fore and try. The smoother is set up to take extremely thin shavings to put the finish ready surface on the show faces of the “money” boards. It leaves behind a tearout free, polished surface that is ever so slightly scalloped. The scalloping is so shallow that you don’t really see it, but if you run your hand over the surface, you can just barely feel it.
So there is my definition of “significant”, “moderate” and “just a hint” of camber as it applies to my personal planes. I’m curious now as to how my definitions of “significant”, “moderate” and “just a hint” compare to yours for your personal planes.