To determine whether a chipbreaker can reduce tear-out, I needed to do a controlled test in which only the chipbreaker distance was changed. If a larger chipbreaker distance resulted in tear-out and a smaller distance reduced or eliminated it, that would resolve the issue.
My first attempt to decide this was successful. I planed the edge of a piece of Bolivian rosewood with a chipbreaker setting between 1/64” and 1/32” as shown below.
Even with a freshly honed blade taking shavings about .001” thick, serious tear-out was evident on the ribbons of wood where the grain direction was adverse. The mouth dimension of the plane for both parts of this test was about .025” or slightly less than 1/32 of an inch.
After planing the entire edge with this chipbreaker setting, I touched up the blade and set the chipbreaker .004” from the edge. Here’s an image of that setting:
To allow better comparison of the two surfaces, I left one end of the board as it was and planed the other end, attempting to remove the tear-out. The results were immediately apparent, and I continued planing until the new surface no longer continued to improve. There was still tear-out, but it was not nearly as deep and was confined to fewer areas. The improvement in the quality of the surface produced was unmistakable.
For a benchmark, I had first planed the other edge of the rosewood using a 12º back bevel, which had given me the previous “best surface” on this difficult timber. That surface was still considerably better than the one produced using a chipbreaker distance of .004 inches. It had only one patch of minor tear-out, otherwise just dullness in the areas of adverse grain.
A Few More of the Specifics:
- Blade: Holtey S53 with a primary bevel of 32.5º and a 2.5º back bevel
- Plane: Spiers unhandled infill plane with a bed angle of 45º
- Mouth Dimension: The combination of the Holtey blade and the Spiers plane produce a mouth dimension of about .025 inches.
- Wood Planed: 8/4 Bolivian rosewood, a brittle timber with rowed grain
Summary of Procedure:
- Plane one edge of the board using a blade with a 12º back bevel, which results in a cutting angle of 59.5 degrees. This represents my previous “best surface.”
- Plane the other edge using a blade with my standard 2.5º back bevel, a chipbreaker set .022” from the edge, and a mouth too wide (at .025”) to be effective in eliminating tearout.
- Set the chipbreaker at .004” and plane half of the surface produced in step 2 to see how much of the tear-out can be removed solely by using a more closely set chipbreaker.