A lot of colloquial words that we might use when describing something’s durability take on extremely specific meanings when a materials scientist or blacksmith uses them. Things like “strength”, “toughness”, “hardness”, and “resilience” all have different meanings when working in a laboratory or industrial setting than most people might otherwise think.
For the beginner metalworker, this can be a little bit confusing at first but some hands-on practice will help. To that end, this beginner lesson in heat-treating steel from [Blondihacks] demonstrates why it can be beneficial to trade some of the metal’s toughness for improved hardness and just how to accomplish it on your own.
The first part of the lesson is to make sure the steel is high-carbon steel, since most other steels aren’t able to be heat treated. It will also have a specific method for its quenching, either in oil, water, or some other medium. But beyond that the only other thing required for this process is a torch of some sort. [Blondihacks] is using a MAP-Pro torch to get the steel up to temperature, which is recognizable when it turns a specific orange color. From there all that’s needed is to quench the hot metal in whatever fluid is called for. At this point the metal can also be tempered, which restores some of its toughness while maintaining a certain amount of hardness.
While the process doesn’t require specialized tools, [Blondihacks] does have a hardness tester, a fairly expensive piece of instrumentation that measures how deeply the metal can be indented by a force. By measuring the size of the indentation made by the tool, the hardness can be determined. As it’s many thousands of dollars this is mostly for demonstration and not necessary for most of us, but does go a long way to demonstrate the effectiveness of heat treating and tempering in an otherwise simple environment. If you’re looking for excuses to start heat treating and tempering metal, here’s a great project which creates a knife nearly from scratch.
Continue reading “A Guide For Heat-Treating Steel At Home”
Intaglio is an ancient carving technique for adding details to a workpiece, by manually removing material from a surface with only basic hand tools. If enough material depth is removed, the resulting piece can be used as a stamp, as was the case with rings, used to stamp the wax seals of verified letters. [Nicolas Tranchant] works in the jewelry industry, and wondered if he could press a CNC engraving machine into service to engrave gemstones in a more time-efficient manner than the manual carving methods of old.
Engraving and machining generally work only if the tool you are using is mechanically harder than the material the workpiece is made from. In this case, this property is measured on the Mohs scale, which is a qualitative measurement of the ability of one (harder) material to scratch another. Diamond is the hardest known material on the Mohs scale and has a Mohs hardness of 10, so it can produce a scratch on the surface of say, Corundum — Mohs value 9 — but not the other way around.
[Nicolas] shows the results of using a diamond tip equipped CNC engraver on various gemstones typical of Intaglio work, such as Black Onyx, Malachite, and Amethyst with some details of the number of engraving passes needed and visual comparison to the same material treated to traditional carving.
Let’s be clear here, the traditional intaglio process produces deep grooves on the surface of the workpiece and the results are different from this simple multi-pass engraving method — but limiting the CNC machine to purely metal engraving duties seemed a tad wasteful. Now if they can only get a suitable machine for deeper engraving, then custom digitally engraved intaglio style seal rings could be seeing a comeback!
Intaglio isn’t just about jewelry of course, the technique has been used in the typesetting industry for centuries. But to bring this back into ours, here’s a little something about making a simple printing press.
There are a lot of ways that metals can be formed into various shapes. Forging, casting, and cutting are some methods of getting the metal in the correct shape. An oft-overlooked aspect of smithing (at least by non-smiths) is the effect of temperature on the final characteristics of the metal, such as strength, brittleness, and even color. A smith may dunk a freshly forged sword into a bucket of oil or water to make the metal harder, or a craftsman with a drill bit might treat it with an extremely cold temperature to keep it from wearing out as quickly.
Welcome to the world of cryogenic treatment. Unlike quenching, where a hot metal is quickly cooled to create a hard crystal structure in the metal, cryogenic treatment is done by cooling the metal off slowly, and then raising it back up to room temperature slowly as well. The two processes are related in that they both achieve a certain amount of crystal structure formation, but the extreme cold helps create even more of the structure than simply tempering and quenching it does. The crystal structure wears out much less quickly than untreated steel, therefore the bits last much longer.
[Applied Science] goes deep into the theory behind these temperature treatments on the steel, and the results speak for themselves. With the liquid nitrogen treatments the bits were easily able to drill double the number of holes on average. The experiment was single-blind too, so the subjectivity of the experimenter was limited. There’s plenty to learn about heat-treated metals as well, even if you don’t have a liquid nitrogen generator at home.
Thanks to [baldpower] for the tip!
Continue reading “Reducing Drill Bit Wear The Cryogenic Way”