Modern Simple Heat Treating Equipment

For Hand Punchcutting in Steel

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1. Introduction

If as a traditionalist you've set up a small forge, then you already have a heat treating setup.

The modern punchcutter, however, may choose instead to employ a propane torch or a kiln for hardening. Tempering may be done with a torch (difficult), in a kiln, on a hot plate, or with a bath of molten typemetal (which sounds exotic until you actually become a typefounder, at which point it becomes quite ordinary).

(Note: The title of this section is meant to indicate modern equipment which is simple and appropriate for the small shop. Heat treating is a specialized industry, and much of the equipment used today commercially is far from simple.)

2. Hardening With Propane Torches

Here is the setup that Stan Nelson used for his 2016 Wells College Book Arts Summer Institute punchcutting class (the location is the entryway to Morgan Hall at Wells College (Aurora, NY), which houses the Wells Book Arts Center).

The base of this hearth consists of an ordinary printer's galley turned upside-down so as to provide an air-space to protect the ordinary fiberboard folding table below. On this is an arrangement of soft firebrick in which is set a nest of charcoal soldering blocks A small metal bucket of water served as the quenching bath (after hardening a dozen punches, it got quite warm - a larger bucket or fewer punches might have been better). The punches are transferred from the furnace to the quenching bucket with an inexpensive pair of long-nosed pliers. Heat was from one or (sometimes) two hand-held propane torches.

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Soft firebrick should be distinguished from hard firebrick. Soft firebrick is a better insulator, but is much more fragile. Hard firebrick is more durable but more difficult to cut; it is heat-resistant, but not necessarily a good insulator. So soft firebrick is the appropriate material for a simple setup such as this. Firebrick is available in various maximum service temperature ratings. I don't know the rating of the soft firebrick that Stan used. I ended up with 2300 degree Fahrenheit brick for my own shop (HWI Greentherm 23 LI), which should be sufficient - W-1 tool steel is only heated to 1,500 degrees when hardening.

The purpose of the charcoal block is to reflect the heat better (rather than letting it be absorbed by the firebrick). As you can see from the view below, it is gradually consumed during use. (Stan suggested that when finished one should wet it slightly by flicking water on it with your hand. Otherwise it can continue to smolder and you risk coming back later to find your expensive charcoal block burned away.)

These charcoal blocks are sold into the jewelry making trade as surfaces for soldering (by flame, not electrical soldering) and silver brazing. Turning to the modern literature, { Untrecht 1968} notes that "The most common surface [for soldering] is a charcoal block" (p. 170). { McCreight 1991} lists the charcoal block as the first of several soldering surfaces, and notes further that it provides a reducing (the opposite of oxidizing) environment. This would serve to reduce the formation of scale slightly.

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(Looking at the photo above right, I wonder if the back firebricks aren't hard firebricks?)

For a similar style of hearth with only a single block of charcoal at the bottom, see Stan Nelson's 1985 film From Punch to Printing Type . For a version with charcoal on the bottom and sides, but without a top, see Stan Nelson's video clip "Hardening Punches and Striking Matrices" from the unfinished film to have been entitled Out of Sorts .

3. Anti-Scale Compounds

[TO DO: Stan uses Red Ochre; research the history of this. Explore other compounds: those of traditional blacksmiths (borax as flux, boric acid based compounds); modern commercial compounds (RBC Anti-Scale Compound (Rose Mill Co.), ATP-641 Water-Based High-Temperature Anti-Scale Coating (via Brownells), the use of Red Iron Oxide).

4. Tempering using a Typemetal Pot

Steel as quenched in the hardening process is very hard and consequently very brittle. It may be made less brittle (but therefore also less hard) by heating it again; the temperature to which it is heated in this tempering process correlates directly to its hardness.

The surface of the steel will develop colors which depend upon the temperature of the steel at any particular point along its length. (These colors are due to varying thicknesses of an oxide layer which forms on the steel.) The colors will change as the steel heats, moving along its length from the heated end to the tip. (In most situations, the desired result is a tool such as a punch where the heated end - the hammer end - is softest and the tip is the hardest.) When the tip of the tool has reached the desired color (and thus desired hardness) the tool is quenched again to stop the tempering process.

Traditionally the blacksmith tempered a steel tool by first cleaning the hardened steel and then heating one end in the forge (or with a torch in more modern situations).

Fournier also describes an alternative practice for tempering punches by using a molten typemetal bath as a heat source. The advantage he cites for this method is that the punchcutter's eyes are "thus saved from being dazzled or tired by the heat of the fire":

"This part of the work can be much more readily performed by punchcutters who possess a typefoundry. They plunge the punch into the molten typemetal, holding it with the pincers so that only the cleaned end remains visible. Their eyes being thus saved from being dazzled or tired by the heat of the fire, they can the more comfortably and accurately secure the colour which they desire and which indicates the right degree of temper." (p. 79 of the Carter translation, p. 66 of the 1764 original)

See the section on Tempering using a Typemetal Pot in the Forge section for references to illustrations of this process using traditional typemetal pots of styles which would have been recognizable to Fournier.

See also the same section for a discussion of how this process differs from the use of a lead or lead/tin bath for tempering in industry.

The modern punchcutter who does not wish to set up a traditional charcoal-fired typemetal pot may draw upon yet another modern field which is unrelated to - indeed, opposed to 1 - typefounding: the amateur casting of bullets. The firms which supply that hobby manufacture small melting pots intended for lead alloys which are suitable for typemetal.

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Here is the punch after tempering (on the left just as removed from final quenching, on the right cleaned up a bit). This was the punch that I made in Stan's class - you can see in the right photo that at some point during hardening or tempering it cracked.

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5. Tempering with a Hot Plate

[TO DO]

6. Annealing Steel (Torch-based Methods)

[TO DO - the issues are in the cooling]

7. Using a Kiln

All three processes (annealing, hardening, and tempering) can be done with greater precision with a kiln.

[TO DO]

8. Sources

The techniques here are those of the blacksmith and (to a lesser extent) the jeweler - both vibrant fields. There is also an active subculture devoted to amateur ("backyard") metalcasting which has increased the availability of refractory materials. And in general the hardening and tempering of steel is one of the core technologies of civilization. So there are many sources for both materials and information.

Soft firebrick may be purchased from any number of sources. I got mine from hightemptools.com. Although I buy many things via Amazon.com, I opted against buying soft firebrick through Amazon because their fulfillment process is designed for speed rather than the protection of goods - and soft firebrick is fragile. Soft firebrick shipped via Amazon might easily arrive as a package of dust.

This particular supplier (hightemptools.com) didn't actually specify the technical details of the firebrick to be supplied, but what they ended up sending for their 9" x 4.5" x 3" soft firebrick was a case of HarbisonWalkerInternational (HWI) "Greentherm 23 LI" Insulating Fire Brick. This is a 2300 degree Fahrenheit brick (hence the "23" in the designation) made by HWI in China.

I did end up getting my charcoal blocks via Amazon. "EuroTool" branded online, but anonymous in their packages, and individually wrapped. They arrived safely. They're surprisingly expensive for a consumable item. They can also be found through regular jewelry suppliers such as Rio Grande.

I was able to find red ochre as a dry artist's pigment on Amazon. I haven't tried it yet.

The two major manufacturers of lead alloy melting pots for bullet casting are Lyman Products Corp. and Lee Precision, Inc. Related suppliers may be found by searching under the term "reloading" (so called because for the most part they are simply re-using existing shell casings, not making new muzzle-loading bullets). For use by the punchcutter (or hand type caster) the models which do not have a spout underneath them are best. Examples: the Lee Precision Melter or the Lyman Big Dipper. These can be purchased from many sources, including vendors via Amazon and more traditional gunsmithing (so called) supply houses such as Brownell's or MidwayUSA

9. Notes

1. Because the pen (type) is mightier than the sword (bullets). Also because the reloaders, who have no idea what a Linotype is, have driven the price of what they call "linotype" (meaning Linotype typemetal alloy) to at least double that which a linecasting operator can afford. They make the already difficult project of keeping linecasting alive even harder.

10. References

{McCreight 1991} McCreight, Tim. The Complete Metalsmith: An Illustrated Handbook. Revised Edition. Worcester, MA: Davis Publications, Inc., 1991.

As comprehensive as Untracht (see below), but more modern in style. Admirably direct; an essential introduction reference. Its current publication status seems to be more complex than necessary for such an important work.

{Untrecht 1968} Untracht, Oppi. Metal Techniques for Craftsmen. NY: Doubleday, 1968.

This is a very good, comprehensive, but quite "old school" (meaning first half of the 20th century) compendium. Naturally, it's out of print, but it's worth getting. If you take a serious jewelry-making class, you can be sure that your teacher, or your teacher's teacher, used Untracht.

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