The following is excerpted from “Sharpen This,” by Christopher Schwarz. I chose this section because I get asked more about smoothing planes – specifically why they leave plane tracks – than anything else sharpening-related in my classes. I’d say that 80 percent of the time, the “problem” is a blade that has no camber. Here’s how to put one on the blades for a smoothing plane and jointer plane (a shallow curve).
– Fitz
The blades for my smoothing plane, jointer plane and block plane have slightly curved edges so that the corners of the iron do not dig into the wood and create “plane tracks.” Plane tracks are the ugly ridges left behind by the cutter’s corners.
To create a slight curve, begin with a blade that has been ground straight across. The curve is generated on the honing and polishing stones.
The first step is to round over the corners of your blade. I do this on the edges of my honing stone.
Why the edges? Because this process cuts a deep gouge in the stone, so the stone’s edges are a good place for it.
The result is that the corners are rounded over with a small radius – about 1/16″ radius.
Now install the blade in your honing guide. To create the curve for the first time on a straight edge, mentally divide the edge into five “stations” along the tool’s edge. One station is in the middle of the edge. One at each corner. And two more between those points.
With the tool on your honing stone, put firm finger pressure on one of the corner stations and take 12 strokes. Then put firm finger pressure on the opposite corner station and take 12 strokes. Now put your finger pressure on one of the intermediate stations and take six strokes. Switch to the other intermediate station and take six more. Finally, put your finger pressure on the center station and take two strokes.
Remove the tool from the honing stone and check for a burr. If you have a burr, hold the tool up in front of your face with a strong backlight. Place a small straightedge on the tip of the edge to see if the edge is curved. If you cannot see a curve, there’s a fair chance your stone isn’t flat; it’s convex across its width. Flatten the stone (see Chapter 9) and try again.
How much of a curve should there be? It depends on the width of the iron and the angle at which the iron is bedded. If you see a curve, continue onto polishing.
Put the tool to use and see if the curve is working (meaning there are no ugly plane tracks). If the curve is too shallow (plane tracks, argh), hone the iron with more pressure at the corners to increase the curve.
If the curve is too pronounced (where the iron will take only a narrow, thick shaving in the middle) then hone again with more pressure at the center station.
For freehand sharpening of curved blades, I press one corner of the bevel to the stone. Then I raise the back end of the tool 1/8″. As I pull the tool toward me, I also shift the pressure on the bevel to the center of the edge and then to the other corner.
Alternately, I’ve heard that using a figure-8 honing stroke will put the camber on the blade. Again, practice is required
Thanks for this. Three questions:
After this initial cambering, I assume you repeat this ”station” process after regrinding the blade at a later date. Do you ever repeat it before that, during future honings and polishings?
Is there something to note in the polishing step? Does the 12-6-2 pattern apply there, or is the aim just to get the edge polished without regard for the number of strokes it takes to do so, trusting that the honing has gotten you the correct camber geometry?
What is the rationale for cambering the jointer blade? If smoothing follows jointing, wouldn’t that be enough to get rid of plane tracks?
Waiting on my book from Rubank!
You repeat the “station” process on each polishing stone so that the blade is polished evenly across.
Every time you hone, you repeat the “station” process to maintain the curve. If the curve becomes too severe, you use more strokes in the middle of the blade. If it is too shallow, you use more strokes at the corner.
Jointer planes need a curved blade so they can manipulate and correct an edge joint. Plus, not all surfaces are planed by a smoothing plane.
Nice, thanks for your quick reply!
Do you have earlier blog posts or videos about finessing edges with a cambered jointer blade? I’m curious, because in my measly two years of woodworking I haven’t yet had a case where I couldn’t get an edge right with partial width cuts on a straight blade 5-1/2 jack plane, but it could be that I just haven’t run into a problematic enough (long enough? wide enough?) edge joint.
This is discussed widely in the literature. Hayward. Wearing. So many others. Almost every traditional source.
David Charlesworth’s “Precision Planing” covers this incredibly well. I normally learn best by reading, but I struggled with getting an edge joint correct with a hand plane until I viewed Mr. Charlesworth demonstrate the procedure in his video.
This little book is a field of diamonds. I am a great fan of Lost Art Press but you guys hit it out of the ball park with this one. Thank you and please keep up the good work.
Agreed. I pulled mine out a few days ago for a brief refresher before I sharpened a card scraper. It was a lot quicker than googling up a youtube or LAP video and satisfyingly non-electronic.
I’m not quite following the first step on rounding the corners. It looks like you’re pulling the corner along the side of the stone, but do you vary the angle to get the radius?
Yes. You can’t show motion in a still photo. Move the plane blade so you get a radius at the corner.
Would you think rounding the corners on the face of a diamond plate be an ok practice? They don’t bond the sides of the diamond plates in my experience with the cutting diamonds.
Sure. Diamonds would do the job nicely.
Could you comment on the camber needed for a low angle, bevel up, plane. I presume that it would be greater than what is needed on a traditional plane.
Yes, it needs more (but how much depends on the angle and how wide the blade)