What is backlash?
Backlash is the term given to the amount of free play in the iron depth adjustment mechanism, and the problems it can cause.
As the plane is being used, free play sometimes allows the blade to move upwards on its own after it has been adjusted to the desired position. It happens after the blade has been adjusted upwards, or retracted slightly, using the thumbwheel adjuster.
What types of adjuster are affected?
There are two main types of mechanism for adjusting the depth of the irons on woodworking hand planes.
One is the mechanism developed by Leonard Bailey in the U.S., and later used by major manufacturer Stanley.
The other is the Norris-style adjuster developed in the UK (see).
Planes with either type of adjuster can suffer from backlash.
Remove the upwards free play
The solution is to always make the final depth adjustment by advancing the blade (turning the wheel adjuster clockwise, as shown) rather than retracting it. This removes free play that could cause backlash from the mechanism, ensuring the iron stays at the right depth.
When reducing the projection of the blade to take a finer shaving, retract it a little more than necessary, then advance it slightly to complete the setting.
It can sometimes take several turns of the wheel adjuster to get the free play out of the mechanism.