Hardening Tools That Won’t Stay Sharp
I
F YOU HAVE DESTROYEDthe hardness in your carbon-steel edge
tools by overheating (turning the edge blue while regrinding),
here’s how to reharden the cutting edge with a relatively simple, three-
step process:
- Annealing. Heat each tool slowly and thoroughly to about
1,450 ̊F (a bright cherry red); a propane torch works fine. Then bury
it in a large container of sand, allowing the tool to cool slowly. If the
tool’s edge can be readily filed when it has cooled, then it has been
properly annealed. - Hardening. After restoring the cutting edge to its original shape,
reheat the tool to 1,450 ̊F, and then quench it by plunging the tool
edge first into a container of soft water. Agitate until it’s cool. Run a
new smooth file over the edge. If the file skates over the edge without
catching, the tool has been properly hardened. It is now too hard to
use, though, so it must be tempered first. - Tempering. Heating and quenching the tool blackens the tip, so
polish it with a piece of fine-grit wet-or-dry sandpaper as soon as
you’ve checked for hardness with the file. Heat the tool slowly with a
propane torch, keeping the flame well back of the edge. When the
edge turns a soft yellow, quench again in soft water.
Heat-treating carving tools in this manner takes practice, so don’t
be discouraged if you have some failures. But learning the art of heat
treating can pay big dividends.
For more detailed information, find a used copy of Hardening and
Tempering Engineer’s Toolsby George Gentry, Argus Books Ltd. (the
book is out of print). It’s a good, basic book on the subject.
—RAYLARSEN,Hanover, Mass.,
from a question by Steve Hamrell, Park City, Mont.
SHARPENING & GRINDING