Cambering Plane Irons

A slight curvature on the cutting edge of a plane iron eliminates track marks produced by the corners of the iron on the workpiece. The most succinct description I have encountered of how a cambered iron works is as follows:

"Imagine a tub of ice cream and all you have to level it with is an ice cream scoop. First passes leaves scoop shaped hollows (width depends on how deep you go). Second pass you remove the top of ridges between the hollows - digging less deep. Third pass ditto." (Jacob Butler) posted on UKWorkshop. May 12th 2011

This is my method of cambering a plane iron, it is quick and easy to do and repeatable with quite a high degree of precision. It is informed by David Charlesworth's technique described in DVD#1 Hand Tool Techniques Part 1 and my own belief in honing guides with a wheeltrack wider than the tool being sharpened (making the guide master of the tool rather than the other way around).

Begin by wetting the lapping film with a few drops of HoneRite No.1, place a rigid steel rule (about 1mm thick) under one wheel of the guide as shown above and hone through 40 30 and 5 micron grades to produce a triangular polished facet on the opposite corner of the primary bevel.













Do the same again with the rule on the other side, then repeat the process using a thin flexible rule to create a shallower polished facet on either side. Finally hone the centre of the iron flat, just as you would for a square edge. This step is important as it broadens the shaving that the plane will take at shallow depths of cut. If you like you can also do alternate strokes with one wheel on the glass and one on the film to help blend the facets into each other. The result should be a plane iron with a smiley face. (please excuse the loss of picture quality, I was racing against the setting sun)













Take the iron out of the guide, turn it over, slip the thin rule under the safe end, and starting with the cutting edge off the sheet, draw the non-bevelled face of the iron onto the 30 micron film to remove the burr. Polish to a shine on the 5 micron again with the other end supported by the thin rule. (this bit is pure Charlesworth and saves a whole bunch of time and effort).

OK the light has really had it now, but this is what you are aiming for - a nice broad shaving that feathers out to nothing on either side:













In this case I'm doing quite a big camber for a jack plane iron, for a smoother the thin rule would be sufficient for the ends and maybe a sheet of good quality paper for the second set of facets. For block planes and bevel-ups you need more camber because the low bedding angle will reduce its effect. The Richard Kell No.2 honing guide I am using here can camber blades with up to 50 degree primary bevels using this method. It can also handle narrow or short bladed and tapered tools that many other guides struggle with.