The most curious style of sawtooth seen anywhere in the world is the Edome style used for Japanese saws. I have attached a diagram below. It is characterized by having an additional facet cut into the point of the tooth. Before I dive deeper into the Edome tooth, I would like to make some opening points about the objective of this post, and some general observations related to saws and wood.
The purpose of this post is for information only. I will only explain one variety of sawtooth and a bit of history surrounding its development. If Japanese saws, or Japanese history, offend your tender sensibilities in any way, please close this post immediately, step away from your computer, and see your healthcare professional ASAP.
There is no profit motive here. This information will be worth every penny you pay for it. My profession is managing the design and construction of large commercial building projects in Japan, not selling saws. I do sell a few tools on the side, but have never sold a saw of any variety to anyone. No one pays me for my scribbling about woodworking or woodworking tools. No one pays me to teach them how to use tools or how to make stuff, other than commercial buildings.
The purpose of this post is not argument. Sadly, too many SC members exhibit chronic reading-comprehension difficulties. Some seem to enjoy argument, combined with posturing, personal insults, and religious denigration. If you are inclined to such juvenile and/or trollish behavior, immediately move along to another thread, perhaps one about sharpening... there is nothing here for you.
A few facts you might find interesting. Did you know that the majority of handsaws sold throughout not only Asia, but also Europe and the Americas nowadays are Japanese-style pull saws with replaceable blades, and that all of those have Japanese-style teeth?
Why do they sell so well? I believe that it isn't because of fashion, but because of performance. Compared to other types of saws on the market, they cut more accurately and efficiently, they are easier and quicker to sharpen (simply replace the dull blade with a new one), and they are more cost-effective. But don't take my word for it. Do the research yourself. Perform some objective hands-on tests. Measure the results. Do the calculations. Until you spend the money and time, and make the effort necessary to confirm their qualities for yourself, your opinion on the subject is as insubstantial as air.
Did you know that the vast majority of wood cut with handsaws around the world is not hardwoods such as oak, maple and beech, but softwoods such as pine, cedar, and fir? So why would you want all your saws to have teeth designed to cut harder hardwoods efficiently, but softwoods less efficiently?
If you are concerned about the relative fragility of Japanese teeth, you should be. They are more easily broken and bent when used ham handedly than the squatter teeth common to Western-style saws. Japan is a group of mountainous islands with few natural resources beyond abundant fresh water and softwood forests. No surprise that the style of tooth used in Japanese saws was developed to cut these softwoods. The more fragile Japanese sawtooth works perfectly for the majority of wood cut with handsaws around the world. But of course, not all woods. A craftsman is wise to match the saw to the job. Just like you wouldn't use a formula 1 car to tow a cement mixer, or a Ram 3500 truck to race through the streets of Monte Carlo, you shouldn't use a conventional fine-toothed dozuki to make deep cuts in ebony or crosscut 4x8 sheets of plywood. A Dodge Ram 3500 is perfect for transporting your little red race car to the starting line at Monte Carlo. This analogy applies to many tools.
If you are concerned about Japanese saws being difficult to sharpen, you should be. But as in all human endeavors, difficulty is relative. What's too hard for a ten year old boy to accomplish is often easier for a more experienced, determined, careful adult. With the right files, a saw vise, and some practice, most people can learn to sharpen a Japanese saw adequately (except the induction-hardened ones, of course). As you would expect, a professional saw sharpener will do a better job than the average carpenter. There is nothing wrong with not being willing or able to sharpen a Japanese saw like a professional. But in my experience, those who say it can't be done have either not tried to do it, or don't have the patience to do it properly.
However, the difficulty of sharpening Japanese saws, and to some extent even the fragility of their teeth, became instantly irrelevant with the introduction of replaceable sawblades.
So, let's get to the meat of the subject, the Edome sawtooth.
"Edo" 江戸 (pronounced "Ehdo") is the old name for Tokyo. "Me" 目 (pronounced "meh") means “eye” but in the case of saws, it refers to a saw tooth. Therefore, Edome 江戸目 is a style of sawtooth associated with old Edo.
Professor Hirasawa (RIP) and Professor Hoshino at the Tokyo University of Agriculture have done the most extensive and in-depth research on the subject of handsaws in Japan. You should see Professor Hoshino's impressive collection of literally tens of thousands of saws. Literally tons of antiques. According to Professor Hirasawa, the Edome tooth was developed in Edo around the beginning of the Tokugawa Shogunate when Tokugawa Ieyasu united the many feudal clans of Japan (through bloody-handed conquest) into one nation in 1603, more or less.
As a consequence of the relocation of the capital from Kyoto to the far away and relatively undeveloped Kanto plains, a new castle and many government buildings were quickly needed. The Shogun also demanded, on pain-of-death, that all the clans and lords construct large and expensive residences and facilities in Edo. In order to guarantee good behavior, they were also required to submit hostages to be housed in these Edo residences for most of the year. The clan leaders and lords were also required to spend several months of every year in residence in Edo, traveling back and forth from their fiefs and lands several times a year in prescribed and expensive processions. One of Shogun Tokugawa Ieyasu's objectives in these severe demands was to cause the warlike clans and stiff-necked lords to spend a lot of their disposable income on construction projects and travel rather than on their more traditional hobbies such as war preparations and fun things like grabbing land and cutting off heads. All these changes caused construction in Edo to boom for a long long time. Primarily wood construction, of course. Good for construction companies, craftsmen, and nation-building, but not so good for feudal lords looking for a glorious dust-up.
With extended peace, the population in Japan boomed. Craftsmen of all varieties were in high demand in Edo, of course. Just as better axes and saws were required to build homes, cities, and towns in North America, better, more efficient tools were demanded by Japanese craftsmen to help them build Edo. Those improvements were developed by the craftsmen themselves, not a designer in Philly or London. The Edome sawtooth was one of those improvements, and according to Professor Hirasawa, it probably occurred early in the Edo period (1603-1868).
No one knows for certain how the Edome tooth was developed, but I like the theory that the extra bevel at the tooth's tip was first added by carpenters who needed to quickly touch up and restore the sharpness of their saws in the field, kind of like the secondary bevel some folks use on their plane and chisel blades. If you look at old saws with Edome teeth, you will notice that many of them have only sharp, uneven stubs remaining. A professional saw sharpener would not do this, but would instead reshape and cut deeper gullets restoring the teeth to the proper shape. But in the field, a carpenter can resharpen an Edome saw quickly and easily by just touching up the tip facet with a file. That's only one small facet to file per tooth. Easy peasy. Obviously, the teeth can become pretty short after a lot of these impromptu sharpenings, and the gullets will not be able to hold as much sawdust. Not necessarily a bad thing when cutting hardwoods, BTW. Give it a try. You will be pleasantly surprised with the results.
I can identify five obvious advantages to the Edome sawtooth:
1. The Edome tooth is effectively shorter than a regular Japanese triangular tooth (Ikedame or Ibarame, for instance), and therefore better supported, and therefore relatively more resistant to bending and breaking. A simple stress diagram will show this to be obvious.
2. The geometry of the Edome tooth has more support for the sawtooth's extreme tip (where nearly all the actual cutting is done) than a regular triangular tooth. This is obvious. The result is that the saw's tip stays sharper longer, and requires fewer major repairs.
3. The Edome tooth cuts better. Less scratching and plowing, and more severing. If you doubt this, run a sharp Edome saw, carefully, over a callus on your hand or foot and feel how it cuts. Repeat this test with a regular triangular tooth saw. You will find that the Edome cuts cleanly and deeply, both on the pull and push, while the triangular tooth sawblade will catch and tear as the sharp points dig in, stall, then jump. You might want to have a bandaid handy when you do this. I think this improved cutting capability is due to the relatively more obtuse (less-pointy) third facet keeping the teeth from digging into the wood deeper than they can effectively cut, while at the same time providing a cutting edge that stays in contact with the wood for a longer period of time, continuing the fiber-severing cut even after the extreme tip has passed by. I suspect it would take some serious time-lapse photography combined with a strain-gauge apparatus to prove or disprove this viewpoint scientifically. On the other hand, a cut callous doesn't lie.
4. The sawblade tends to cut longer. Let's analyze this. Sawteeth become dull in two ways. (1) The cutting-edge bevels dull; or (2) The tips bend or break off. When the tip of a regular triangular tooth dulls, bends or breaks, that tooth stops cleanly severing wood fibers and starts to gouge, scratch, and plow its way through the wood because the fiber-severing action relies mostly on a sharp tip. The Edome tooth effectively has a wider tip, not as easily bent, broken, or dulled, and even if the extreme tip dulls, the sharp remainder of tip facet can still keep cutting.
5. The Edome sawblade tends to bind less in the cut on the return stroke because the extra bevel is ideally suited to severing proud fibers in the kerf on the backstroke. In other words, the fuzz that remains in the kerf, increasing friction on the sawblade, is severed on the return stroke by this additional tooth facet more effectively than the back side of a regular tooth can sever it. The result is that the blade experiences less friction. This is a big deal for Japanese pull saws because, having a relatively thinner blade, they more easily buckle and kink on the backstroke.
The disadvantages to the Edome sawtooth are that it takes an extra step to sharpen each tooth, and it takes careful attention to keep the tips all in a straight line without ups and downs.
In conclusion, the Edome sawtooth is both clever, and effective. Give it a try.
Stan
Edome drawing 11.jpg
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Originally Posted by Steve Pippins
