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Much has been written about the importance of a true and flat plane sole as a key to achieving optimal results during planning. Premium planes come with a very flat sole, do not need any interventions, and are ready for work straight out of the box. Unfortunately, this is not the case with second-hand tools such as planes bought in flea markets or on eBay, and new inexpensive planes. To make these tools worthwhile and effective, we have to flatten their soles by abrading their underside on a sandpaper or diamond media that is backed up by a flat surface. Over the past twenty-five years, I have flattened dozens of planes. Most were my own, many belonged to the woodworking programs I taught in, and a few were owned by friends or my students. I trued cast-iron planes made by Stanley, Record, Miller Falls, Sargent, and more. Some of these planes were short and narrow, while others were long, heavy, and wide. The longest plane I worked on was a #8 Record jointer plane, and the shortest was a small luthier plane by an unknown maker.
In this entry and those that will follow, I will demonstrate my technique of flattening plane soles. I will begin the tutorials showing how to reform a block plane over a diamond stone and conclude this series by indicating how I flatten a # 8 record jointer plane.
Truing and Flattening Principles For All Abrasive Media
Our goal throughout the truing process is to remove material from the high points of the sole until we even out the high and the low areas into one true and flat plane (surface). Some planes will have concave, convex, twisted, or a combination of all the above and it is up to us to attempt to get them to be as flat as possible.
On top of using a good quality straight edge to check our progress, we need a system of visual indications to inform us of the progress we make, how much material has been removed and where precisely the abrasion takes place. Many use a sharpie pen and crisscross the sole with lines, while others “paint” the sole with marking blue (a thin, alcoholic based stain). The sole’s highest points will abrade first as we begin passing the plane back and forth on the abrasion media, and instead of the black sharpie lines, we will notice the shiny surface of the freshly exposed cast iron. As we progress, the areas of polished cast iron will increase their size and gradually take over the entire sole. Once the sharpie lines (or the marking blue) are no longer visible, we can confidently conclude that the sole is flat. At this point, we should introduce a straight edge to the sole and check for flatness along and across the newly exposed surface. We check for flatness against a lited background and see if any light can penetrate between the edge of the ruler and the sole of the plane.
Among all the block planes that I flattened, the Stanley # 60-½” (12-960) takes the lead as this model has proven to be an excellent companion in my shop. The 60-½ Low Angle is short, narrow, and not too heavy. If you invest in a reputable aftermarket blade (to replace the factory one), you will boost its performance even more, so it can be almost indistinguishable from the high-quality planes such as Lie Nielsen or Veritas.
The advantages of diamonds as a flattening media are pretty profound. With the resilient diamond stone, you can continuously abrade the plane’s sole without the annoying need of replacing it periodically – as in the case of sandpapers. If the sole is in bad shape, I like to begging the flattering with a 120 grit diamond stone followed by a 220 grit (or 325 grit).
Next, I will talk about flattening short to medium-length planes over sandpaper media.
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