Ask ten woodworkers to explain what they mean when they use the term register chisel and you’re apt to get ten different answers. Some people will refer to them as “registered” chisels, indicating that the tools have been placed on a list hosted by some higher authority. Others might tell you that the tool was manufactured under the terms of a Royal Patent. As Churchill said, it’s rather “a riddle, wrapped in a mystery, inside an enigma.”
Among the many meanings of the word register, Webster gives these for our consideration:
- to make or adjust so as to correspond exactly,
- to be in correct alignment, or register
Many craftsmen of the bygone era (including carpenters, millwrights and machinists) would use the word register to indicate a surface that must mate exactly with another or one to be used as a reference datum for measurement.
Register chisels have these characteristics; square sided, thickly made and only slightly tapered (is at all) in section, hooped, ferruled (typically with a shock washer),
the handle is parallel to the back and the back is flat.
The flat back is very specific to a register chisel. It allows for heavy (minimal clearance angle) cutting on a “register” i.e. cleaning up mortise cheeks after boring or a gain. Large surfaces which require flattening, i.e. bridles and laps can be accomplished with socket firmers or slicks. These tools do not (typically) have flat backs and handles are set above the tool’s center axis. Socket firmers are either “lightly” driven with a mallet or pushed for paring. Slicks are only pushed.
While a flat back would seem to be the norm, most tools warp during the hardening and tempering process. For most chisels, a slight warp (in the right direction) isn’t a problem. However, grinding or some other method of straightening is required to insure a perfectly flat back, as on a register chisel.
So this is the explanation that was given to me nearly sixty years ago. I’m going to stick with it unless or until someone gives me a better one.