Exploring Japanese saws (ii) – teeth and blades

This post looks at the functional components of a saw – the blade and teeth.

“The Japanese saw (Nokogiri) is more delicately made than the English one, but I do not hesitate to state that the Japanese tool is decidedly the better of the two in principle as a cutting instrument. Firstly, it will be seen that the blade is in tension when cutting, and therefore a thinner blade can be used, and the ‘kerf’ or waste wood, be reduced. Secondly, the teeth are long, and the cutting points are properly formed to produce a cutting, and not a scraping, action.”

George Cawley, Wood, and its application to Japanese artistic and industrial design, p.194-223, Transactions and Proceedings of The Japan Society, London. Vol.II (1892-93)

Teeth

One of the things that differentiates Japanese saws, both from Western saws, and from each other is their teeth. The same form of saw can have different teeth, which therefore makes its utility different. Saw teeth classically come in two configurations: cross-cut and rip. However they often use different teeth patterns for softwood and hardwood, and as Japanese craftsman use predominantly softwoods like pine, cedar, white oak, and Japanese cypress, the softwood pattern is often the most common.

Rip teeth

Rip teeth, which cut along the wood grain are known as tatebiki. Rip teeth are wedge shaped with sharply pointed tips. The teeth to cut softwoods have a sharp angle so they can “bite” the wood, whereas the hardwood teeth have a larger angle which adds strength and prevents the teeth digging in. In many rip saws teeth are graduated from large to small from toe to heel. This allows for an easier start to sawing by using the back of the saw for the first few cuts and then transitioning to the entire blade.

The basic tooth geometry for crosscut and rip saws

Crosscut teeth

Cross-cut teeth cut across the wood grain and are known as yokobiki. Crosscut teeth are not pointed, but instead have a chisel-like finish, with multiple cutting edges. These points score the wood so that it does not tear. The general shape of cross-cut teeth is very different to their western counterparts. Like the rip saw, the saws do vary for softwood and hardwood – the shape is not altered, however the bevel of the upper cutting edge has a greater angle for hardwood. The teeth normally have a small amount of set, however some crosscut saws have no set, e.g. flush cutting saws.

Tooth shape for crosscut and rip

Cutting edges for crosscut saws: softwood versus hardwood

Hybrid teeth

Rip and crosscut right? It would be unwise to think things were that simple. There are additional types of teeth that are a combination between ripping and crosscut teeth, sharpened like knife-points instead of chisel-points. In Japanese these are known as ibara-me teeth for softwood and nezumi-ba teeth for hardwood. They are often used in saws suitable for cuts other than the traditional 90 degrees. They are filed like crosscut teeth to score the wood, and have the large maw of rip teeth to remove waste expediently.

Different types of hybrid teeth

In recent years another tooth configuration has appeared, the ikeda-me for use in cross-cutting. This tooth configuration generally has a series of cross-cutting teeth to score and cut the wood, alternating with a couple of ripping teeth to clear out the kerf. For example, Hishika have an improved Dozuki saw with an ikeda-me style tooth configuration, allowing crosscut, rip, and diagonal cuts to be made. Their configuration includes a special clearing tooth every 2-3cm to clear out waste.

Some manufacturers also have their own teeth innovations. For example Gyokucho have a configuration known as Hijirime on some of their saws. This provides for a variation in the height of the teeth edges four normal size teeth, followed by four lower teeth, etc. It supposedly improves cutting quality with the lower edges removing waste.

Teeth-per-inch

Saws are often differentiated by their coarseness, or teeth-per-inch (TPI). The finer the teeth (higher TPI number), the cleaner the cut surface will be. Conversely, the rougher the teeth (smaller TPI number), the faster the cut will finish, but the rougher the cut surface will be. Blades for cross-cut generally have a higher TPI number, while those for rip-cut have a smaller TPI number. Some Japanese manufacturers have opted for a more metric term, and instead use the term X/30mm, which is really just the number of saw teeth (X) in 30mm, versus 25.4mm (1-inch).

Impulse-hardening

The teeth on most replaceable blade saws are impulse-hardened. This means that the the cutting edge is heated for 0.003−0.005 seconds by applying an electrical current at 27.12MHz. Most manufacturers will provide some information on teeth hardness – some will provide information on both teeth hardness, and blade hardness (they are different).

There are generally two methods of measuring hardness described by saw manufacturers: (i) Vickers Hardness (VH) number, and (ii) Rockwell C Scale hardness (RC). These tests measure the hardness of a material as its ability to resist permanent deformation from an applied force. A higher value implies stronger and harder steel, which in turn means longer edge retention, at the expense of durability, i.e. the teeth are more brittle.

For example the teeth on Z-Saw saws are hardened to HV800-950 (64-68 RC), whereas those on the G Razorsaws are impulse hardened to HV900-1200 (67-70 RC), and the Nakaya saws are hardened to HV900 (RC 67). How much harder is a Japanese teeth? If we take a Western saw with teeth rated at 52 RC, and a Japanese saw with teeth impulse hardened to 64 RC, then the latter would be about 58% harder.

Saw blades

Due to the fact that pulling a blade puts it in tension, there is less chance of bending or breaking the blade, and as a result the blade can be made extremely thin. Hard, brittle steel can be used to construct the blade, and due to the fact that the blade is so thin, it will cut a narrow kerf, and cut fast. The thin blade also allows for delicate, precise cuts.

Western saw blades are anywhere from 0.02-0.032” (e.g. Lie-Nielsen 0.51-0.81mm) in thickness. Japanese saws are much thinner. Some of the thinnest saws are only 0.2mm in thickness (that’s the thickness of two sheets of paper), and the thickest saws, typically Ryoba are 0.7-0.9mm.For example, some Dozuki saws made by Hishika have a blade thickness of 0.2mm. The kerf is the thickness of the cut made by the blade, and Japanese saws tend to have a narrow kerf.

Blades are also much harder than Western saws. Saws manufactured by Z-Saw are made of steel which has a hardness of HV540-580 (52-54 RC). In comparison, many Western saws, e.g. panel are in the range 49-52 RC.

Hand made blades often have a blade whose thickness is tapered, with the end teeth thin, and gradually becoming thicker near the handle. Some saws, also have sat is known as a “woodpecker tooth” which is used for pocket cutting.

Next up: saw types

The scale of the woodworking for Sears kit homes

People today talk a lot about prefab or modular homes as a solution to the lack of housing, or as a means of building houses in a relatively rapid fashion. There are a number of companies that construction these type of houses, but they always seem to be treated as “new” ideas. I would imagine some of the building processes are newer, making things more streamlined, however the idea is at least as old as the Sears Modern Home. Sears sold over 100,000 houses in 447 styles over the period 1908-1940. Unlike their modern counterparts, Sears took the process uber-seriously. They weren’t the only ones – Montgomery Ward, Eaton’s in Canada, and the pioneer in mail-order homes The Aladdin Company, also produced prefab houses.

Modern machinery helped Sears make kit homes

These houses were exceptionally well built, and some still exist today. Once someone picked a design and any extras, the material for the house was collected in the factory, packaged, and then shipped to site, where it would be assembled (we’re talking circa 30,000 parts per house). Everything was included – wallpapers, paint and varnishes, lathe, shingles^✣, roofing and windows (except for foundations, masonry, and things like plaster). Pre-cut lumber, when it first appeared in 1916, supposedly reduced construction time by up to 40%. The houses were generally designed using the balloon framing construction style, and clad in cypress shingles, masonry or stucco. The interior was finished with high quality materials such as oak, pine and maple woods. Sears “Honor Bilt” ready-cut homes were “based on the same labour and money saving principles as the modern skyscraper“, i.e. the steel for skyscrapers was measured, cut, and fitted at the mills, and just assembled on site ^✻.

The Elsmore (1923)

The Kilbourne (1923)

But it may be the scale of the woodworking that is the most interesting. Sears had manufacturing factories and warehouses for doors, windows, moulding etc. But not small warehouses. By the mid-1920s their down and windows warehouses had 90,000-100,000 pieces of inventory – each. Their production facilities included a 17-acre millwork factory in Norwood, Ohio, a 40-acre lumber yard and factory in Cairo, Illinois and a 50-acre lumber mill and factory in Port Newark, New Jersey – total yard capacity was an incredible 14,000,000 feet of lumber. White pine came in widths of up to 24 inches. White pine from California, oak from Kentucky, yellow pine from Louisiana and Mississippi, birth from Wisconsin, and Louisiana red cypress. The framing lumber, predominantly yellow pine came from close-grained virgin growth.

One of the rainproof lumber warehouses – Every piece of framing lumber is protected from the elements.

Sears produced prefab houses until 1942. Sears started offering mortgages in 1912, but the defaults during the Great Depression, foreclosures, and the lack of resources/curtailment of nonessential construction associated with the onset of WW2, likely contributed to its decline. How much did these houses contribute to the overall housing stock? Well according to the 1940 Census on Housing, there were approximately 17,051,962 dwelling units in the US (which included apartments). Factoring in approximately 100,000 units built by 1940, it contributed less than 1%.

✻ Efficiencies were likely replicated on the Aladdin Readi-Cut System of cutting lumber, which reduced waste – basically Aladdin would get 20 feet of cut board from a board only 16 feet long. During the early 1900s, it was estimated that 25% of good lumber was wasted during construction. Aladdin’s mantra was that they could reduce the waste to 2%.

✣ Interestingly one of the features of these houses was the ability to request “Oriental Shingles“, essentially asphalt shingles covered in granulated slate and guaranteed for “17 years”. Introduced in 1903 they were touted as being “almost fireproof”.