One of the most common errors when planing is to create a gentle banana shape on one face – where the ends of the board end up thinner than the middle.
The cause of this problem resides both in you and in your tool. First off, divide the sole of your plane into two regions: The infeed side of the sole before the blade (the toe). And the outfeed side of the sole behind the blade (the heel). And remember this: The blade of your plane isn’t co-planar with the outfeed side of your handplane.
This feature makes it different than your power jointer. As a result, a handplane has more of a tendency to make bananas. (By the way, you can make bananas – and wedges – with a power jointer as well).
But I think the tool’s role in banana-making is a minor problem. The bigger problem is you and where you are putting pressure on the tool as you plane. Here’s how it’s supposed to work:
At the beginning of the cut, plant the toe of your tool firmly against the work. With the hand on the front knob, put all of your downward pressure right there. Your other hand (on the tote) should only push the tool forward.
As soon as the entire sole is on the work, you should shift your pressure: Use equal and forceful downward pressure with both of your hands.
As soon as the toe runs off the end of the board, release the pressure there but continue to exert downward and forward pressure at the tote.
This work, but it can be a trick to remember for beginning planers. It’s hard to get all your muscles lined up. So I tell them this simple mental trick: Just try your darndest to plane a big old hollow valley in each board by scooping out the middle.
Planing a hollow in this manner is almost impossible to do with a handplane that has a flat sole. So what you wind up with is a board that is fairly consistent in its thickness.
I cannot take credit for this mental trick, but I can’t remember who told it to me years ago. But works like crazy. And with that aspect of planing under control, you can then turn your attention to removing cupping and twisting in your boards.
— Christopher Schwarz