Popular Woodworking 2006-11 № 158, страница 21

Arts & Mysteries

Sandstone leaves a surprisingly fine edge. It's easy to see the secondary bevel I honed with a whetstone in this picture. The edge and entire breadth of the bezel is curved - a result of the shallow groove in my grindstone.

Not a great looking edge, is it? It's a bit like the opposite of a Japanese chisel. This chisel had a flat back nine months ago. The dished whetstones I've been using are slowly wearing away the edges. When that dubbed edge is polished it will cut well, though.

should produce a little less than .003" of hollow in a VV'-thick plane iron ground at 30°. I never saw any hollow on any tool I ground on it. My tools came off the grinder smoother than I thought they'd be, with flat or slightly convex bevels.

Honing

After the grinder, I took my tools to one of the many whetstones I used for this project. None was perfectly flat, but that didn't seem to matter for the beveled side. All of the plane irons I sharpened were cambered and the chisels were too narrow to care about a little dish in the stone. But I quickly realized that none of these old whetstones was coarse enough, or cut fast enough to refine the ground bevel. I couldn't practically remove the camber in the bevel.

Without the ability to hollow grind, and without the ability to fix the grind with a whetstone, period craftsmen probably had no choice but to grind low and hone a secondary bevel (as I did). Maybe this explains Moxon's low angles.

The dished whetstones presented ever-increasing problems with my tools' backs. I tried to do as little as possible to the backs, but creating some amount of back bevel was inevitable. I have seen many old tools with this sort of sharpening (and have lapped out many such problems). In use, I found no disadvantage in this sort of edge. The big advantage of flat-backed tools seems to have more to do with sharpening them than using them.

Conclusions

Despite a few problems with crumbling edges (possibly caused by insufficient polishing), I had little trouble with the tools I sharpened using the old gear. In general, they felt like tools I had sharpened on modern equipment and used for a few days. Not at their peak, but OK. I think it's generally true that period craftsmen had tool steels every bit as hard as our own, but lacked the abrasives to hone them as we do today. As a result, I suspect they worked with tools that were not quite as sharp as ours and had edges that resembled a double-beveled knife.

Not all of these experiments have value to modern woodworkers. Perhaps this one fits into that category. But I guess if pushed I could say a few things that may help:

1) Our modern sharpening technique is based on good abrasives. We use essentially 21st-century abrasives on 18th-century metals. When our metals catch up to our abrasives (CPM-3V is one possible example of a very difficult modern metal to sharpen) we may need to revisit this article.

2) The shapes we hone may have more to do with sharpening than using. A flat back and hollow grind (the way I shape my edges) certainly isn't necessary for use.

PERIOD STEEL

The type of steel used would certainly affect one's sharpening experience. It is my understanding that 18th-century craftsmen could have worked with a wide variety of metals including relatively soft, case-hardened wrought iron, inconsistent cementation (a.k.a. blister) steel and cast steel. The latter two were often laminated to soft wrought iron (to save the cost of steel). Both were capable of achieving high hardness (Rc 65), though it's unclear such a hardness was desired or achieved. I found laminated blades much easier to grind. All of the tools I used during this project were "cast" steel. "Cast steel" was not developed until mid-century and its widespread use is questionable after that. But, we know cast steel was commonly available in a wide array of edge tools by the century's end. Cast steel is not cast iron, nor is the tool cast. Rather, the

3) Based on this experiment, I'm no longer confident that my old tools sharpened with modern equipment are as representative of tools sharpened in the 18th century as I thought. This has caused me to reconsider the ease with which 18th-century craftsmen surfaced stock for example. Smooth surfaces in difficult woods may have required special attention. Either the craftsmen needed to spend extra time on his blades, or scraping or sanding (gulp) may have been required. PW

term refers to the method of manufacture of the steel itself. Iron was melted in clay crucibles, cementation steel was added and the molten metal was cast into ingots. While cast steel was a significant improvement over earlier blister steel in terms of its consistency (specifically carbon content), it's not at all clear that it presented a significant difference in sharpening. — AC

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Popular Woodworking November 2006