Hand-Sharpening Plane Irons

Woodworkers discuss how to sharpen and "round" a smoothing plane iron. October 28, 2005

What is the best way to round a plane blade?

Forum Responses
(Furniture Making Forum)
From contributor A:
I use and sharpen a lot of hand tools and it is easy to round a plane iron if you are already adept at honing edge tools. The rounding of plane irons is done on smooth planes and the like to prevent the sharp corners of the iron from making lines in the planed surface. It actually needs to be a very subtle or slight rounding in order to work. While you are honing, apply a subtle transfer of pressure to the left for a stroke or two, then work back to the center, then to the right for a few strokes and so on for each stone, or whatever sharpening medium you are using. It works like a charm!

Once upon a time I thought that the iron had to be rounded during the grinding process, but this is not the case. Do your grind in the normal manner and then hone as described above for wonderful results. I must emphasize that it is a subtle rounding that prevents the plane marks. You will not be able to detect it with your eye.

From contributor B:
To contributor A: I have to disagree with you on one point. When you round a smoothing plane it is much more than barely perceptible. I round mine as much as 1/32" lower than the center. I have been hand planing for more than 15 years now and this is the curvature that I have found works best. If you have a very flat and true board your method might work. The boards I hand plane are usually wider than 10" and have a slight cup in them (1/16" or less). If you have a very shallow curve on the blade you won't be getting much hand planing done quickly. All of your other advice is on the money.

From contributor C:
I agree with contributor A. To contributor B: You are describing a scrub plane, or a mild version of one.

From contributor A:
To contributor B: There is more than one way to do almost anything. Why not post your rounded plane iron sharpening regimen? I would love to read it.

From contributor B:
I will describe how I sharpen a smoothing plane. This is a plane that will put a surface on a large area such as the main surface of a raised panel or a style or rail of a door.

First, I start off by honing the blade to the proper angle, 25º in my case for the Stanley smoothing plane. For this I use a heavy grit diamond stone (220 grit) and start to get the burrs off and put the round on the blade. I do this by transferring the pressure to the edge of the blade, while pushing forward, instead of the center, making sure to keep the strokes even on the right and left sides. The first time it takes a while because I am going from a straight edge to the curved edge. If I had a 400 grit diamond stone, I would use it to give the now rounded blade a medium polish. On a new blade, at this point I would flatten the back with the 400 grit stone. Then I progress to the 700 grit diamond stone and get a good polish on the edge. Then I fold over any burrs towards the backside of the blade and flatten the back, taking any burrs off.

If I am going to be planing or smoothing pine, I would do a double bevel on the edge, adding a second edge of about +5º. Lately I am hand planing poplar and I only use a single bevel. I end at 700 grit - going any further just makes the edge more prone to getting nicks. I also wet the diamond stones with water while honing.

With any other style of plane blade I always want a straight square edge, with no rounding whatsoever. If you are getting marks in your wood, you need a wider plane, or you need to be more accurate with your guiding of the plane. The main reason for a plane from the good old days was to get a true square edge (except for the smoothing plane). We now use a jointer for this.

From the original questioner:
I am referring to smoothing and not getting tracks in the wood. I usually do my sharpening on a Tormek. Rounding a blade on this device is a pain if the wheel is not perfectly flat. I will now invest in some stones and try it out.

From contributor A:
To the original questioner: I wanted to pass on a tip for hand honing since you will be buying some stones. The thicker the steel is in an edge tool, the easier it is to learn to feel when you are holding the bevel flat on the stone. I suggest you start by practicing on your widest chisel. A wide chisel has thick steel and the thicker the steel, the wider the bevel will be. The wider the bevel is, the easier it is to feel when it is held flat. You will be doing yourself a favor if you learn to do this honing by hand, without honing jigs. That only makes a lengthy process even longer.

Once you learn to feel it in your hands on a chisel, it will be much easier to feel it on the narrow bevel of a plane iron. After mastering that you can move on to the more advanced technique of rounding the smoothing plane iron's bevel and then rounding its micro bevel.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor D:
I've been hand planing wood for over 35 years. Contributor A is correct, the curve on a smoother plane is barely perceptible, about the thickness of two or three sheets of paper. The corners are rounded off to prevent them from digging in and leaving lines on the board.

Contributor B is describing a jack plane (not a scrub plane). A jack plane has a more pronounced curve to remove marks left by scrub planes and to flatten boards. It is especially good to use on board edges to square them. The curved edge helps to turn an edge that isn't square by holding the plane off-center while planning. More wood is then removed by the blade center than the blade edge, thus turning the edge square. I also slightly round the corners of my jack plane, similar with my smoother.

Contributor C is mistaking a jack plane for a scrub plane. A scrub plane has a downright vicious curve, and is used to rapidly hog down rough cut or riven boards that need a lot of wood removed from high spots quickly. Follow it with the jack plane to flatten the board, and after that use the smoother only if you need a fine surface. Sanding isn’t needed after touching with a smoother.

A joiner plane is a very long plane used only to straighten and join two board edges for gluing. It is ground flat and square (no curve and no rounding the corners). Clamp both boards together so that the edges being joined are planed at the same time. If the edge isn't exactly square don't worry, as when rotating one board up to make the edges of both meet the angles will cancel each other out and the boards will glue up perfectly straight.