What to do with worn-out tools?

[Dean Center]

I vaguely recall someone with more metallurgical knowledge than I explaining that the shafts of tools were not hardened because the softer, annealed steel was better at dampening vibration. If so, there may be an advantage to only hardening the fluted portion, at least in the opinion of some toolmakers.

 

[Hy Tran]

Couple of comments:
(1) It is difficult to heat treat only one portion of a tool (pointy-end) and not the other (shank). Heat treating modern tool steels requires controlled heating, cooling, and re-heating. If you really care, I can point you to the scientific literature, but that will put most people to sleep. Therefore, I find the argument that some tools have un-hardened shanks to be somewhat dubious.
(2) Don't confuse hardness (which is resistance to permanent deformation) with elasticity ("springiness"). Hardening a steel has very minor effect on the modulus of elasticity and internal damping. Internal damping in steels is pretty small (again, if you want, I can point you to the scientific literature)--the damping of vibrations occurs from your grip on the handle, the interface of handle to tool, etc.

Best,

Hy

 

[Don Wattenhofer]

Couple of comments:
(1) It is difficult to heat treat only one portion of a tool (pointy-end) and not the other (shank). Heat treating modern tool steels requires controlled heating, cooling, and re-heating. If you really care, I can point you to the scientific literature, but that will put most people to sleep. Therefore, I find the argument that some tools have un-hardened shanks to be somewhat dubious.
(2) Don't confuse hardness (which is resistance to permanent deformation) with elasticity ("springiness"). Hardening a steel has very minor effect on the modulus of elasticity and internal damping. Internal damping in steels is pretty small (again, if you want, I can point you to the scientific literature)--the damping of vibrations occurs from your grip on the handle, the interface of handle to tool, etc.

Best,

Hy

I suspected that was the case and was hoping that someone with the knowledge would step in and clear it up.

 

[Dean Center]

Couple of comments:
(1) It is difficult to heat treat only one portion of a tool (pointy-end) and not the other (shank). Heat treating modern tool steels requires controlled heating, cooling, and re-heating. If you really care, I can point you to the scientific literature, but that will put most people to sleep. Therefore, I find the argument that some tools have un-hardened shanks to be somewhat dubious.
(2) Don't confuse hardness (which is resistance to permanent deformation) with elasticity ("springiness"). Hardening a steel has very minor effect on the modulus of elasticity and internal damping. Internal damping in steels is pretty small (again, if you want, I can point you to the scientific literature)--the damping of vibrations occurs from your grip on the handle, the interface of handle to tool, etc.

Best,

Hy

Thank you for clarifying. All my homemade hook tools have hardened tips and annealed shafts, but they were hardened and tempered by heating with a torch. If I understand what you're saying, in commercial production a batch of tools would go entirely into some sort of oven or furnace, with careful time and temp controls, and the whole piece of steel would be treated. This makes sense, and I appreciate learning that the steel doesn't lose any important to the user qualities in the process.

 

[Hy Tran]

Thank you for clarifying. All my homemade hook tools have hardened tips and annealed shafts, but they were hardened and tempered by heating with a torch. If I understand what you're saying, in commercial production a batch of tools would go entirely into some sort of oven or furnace, with careful time and temp controls, and the whole piece of steel would be treated. This makes sense, and I appreciate learning that the steel doesn't lose any important to the user qualities in the process.

Dean,

If your homemade tools are made of a primarily carbon steel, you probably can harden and temper the tips with a torch. If they are a more exotic alloy tool steel, you would have had difficulty getting optimal hardness--the tempering cycle (where you reduce the hardness of the steel to improve toughness) is typically an hour or more at fairly elevated temperatures (on the order of 400F or more for A10 steel, but the the exact temperature depends on the alloy and the desired final hardness). Now, it is possible to selectively case-harden the steel (hardening just the surface) with some exotic treatments, but let's not put our readers to sleep

Consider M2 tool steel, which is a popular, relatively inexpensive high speed steel for lathe tools: You can explore the Crucible website for heat treating instructions for M2. A really good reference (but not free) is the ASM Metals Handbook.

For many toolmakers, finding a good heat-treater is their competitive advantage. Good heat-treating equipment is expensive--and it's not just controlling the temperature--you also need to control the atmosphere surrounding the tool during heat treatment. I suspect that your typical lathe toolmakers will send an entire batch of tools (after machining to near-final-shape) to their preferred heat treating contractor to handle hardening and tempering the tool. They will then grind the edge (if a premium tool maker) and put the handle on the tool (if a handled tool).

"High speed steel" is a generic term for an alloy steel that retains its hardness at elevated temperatures--typically at the edge of the tool when it's cutting metal.

For the original topic: I've bought some used tools that have been ground pretty short by the original user over the years. Un-handling the tool so you can continue to sharpen is one good approach--200F or 250F for an hour in the oven to soften the adhesive in the handle, and pulling the tool out of the wood handle, then, make a detachable handle. Another good use is to repurpose (for example, making a pyramid point tool). At some point, you just have to consider throwing the tool away...

Best,

Hy