Wiley Horne
David, Winston and all,

THOUGHT 1:
Added advantage of the hollow....It’s not unusual to discover that a Japanese plane has a bump in the center of the dai, behind the mouth. Not sure of all the reasons how this happens, but one reason can be that the blade is fit too tight, (which is something I’m prone to).

How does the bump happen? Well, the plane is likely to be bedded at 40 degrees or so, and the dai is not tall like a western woodie’s body. So there's not much wood under the blade, and the mouth has cut the strength away from it. When the blade is tapped into place—or hammered!—the wood under the blade may bulge, producing a bump in the middle of the sole, right behind the mouth.

If the sole is checked with the blade removed, you don’t see this bump (if it’s there). The sole has to be checked with the blade installed and at cutting depth. Matsui Measure makes a straight edge with a notch in it for this purpose:

https://www.ebay.com/itm/Japanese-Single-Bevel-Straight-Edge-40cm-woodblock-plane-Matsui-Measure-Kanna/193523629312?hash=item2d0ee83d00:g:QqYAAOSwqDVe6uEc

This straight edge can be used to check the sole with the blade at depth—you just place the notch over the blade. Incidentally, they’re hard to find—Hida Tool is stock out. I got mine from SoYamashita at Japan-tool.

My point: check for this bump, with the blade at cutting depth. If it’s there, redo the hollow with the blade installed, so as to cut the bump away. And then consider whether the blade is too tight.

THOUGHT 2

On lapping stuff. I love to lap things. But sometimes scraping or filing is essential. Recently, I bought my first Bailey #3 off ebay, prompted by something Sir Wm. said. A Pre-WW1 model. It too had a bump in the sole, this one in front of the mouth. Which creates erratic performance that’s hard to figure out. Eventually, I found the problem, using that Matsui Measure straight edge. You can’t lap out a convexity, or I can’t anyway. It just stays there pretty much. So I filed this one away, not having a metal scraper.

In general, a double-iron plane is more resistant to sole imperfections than a single iron plane, which has to be about perfect to work right, with the front of the mouth sitting down hard on the work. But this double-iron No. 3 also wouldn't work right until the bump in the sole was removed.

That’s all! Wiley