Blackburn Tools

One of the most frequent questions about my saws is why I use a lamb’s tongue on the end of some backs. While I have tried to come up with a credible story that involves swashbuckling pirates on the Spanish Main, the truth is that it arose from an accident.

My interpretation of a lamb’s tongue at the end of a back.

The first batch of saws I made were all to have backs with traditionally rounded ends. The detail is classic and pleasing, and the first few turned out just as planned. With the confidence bred by past success, I began to trim another of the backs to length. A sixteenth of an inch into the cut, I noticed a line 1/4″ to the side of my cut. With a sinking heart (and a hearty “Arrr, blow me down!”), I paused to identify it as the cut line I had scribed seconds earlier. Now, as any good mechanick knows, an errant cut invariably falls not on the waste side, but on the portion of the stock which is to be used; this was not to prove the exception.*

Loathe to discard an otherwise fine piece of brass in which I had invested good time and hard-won booty, I mulled over my options. The most sensible of these may have been to finish cutting the back short, then trim the saw blade back by the same amount, but that seemed wasteful. A better option was to find a way to conceal the mistake.

Armed with a meager design ability and vocabulary, I quickly settled on my old standby embellishment, the lamb’s tongue. After a few quick sketches, I had a workable design that hid my error. I was happy with the look, and thought that it helped to balance out and soften the many straight lines on that end of the saw.

To my mild surprise, the detail was well received by customers and friends.  With about 75% of the saws I send out featuring that detail, what began as a coverup has turned into a hallmark of my work.

And aye, thar be the true story.

*I could offer up countless stories attesting to the verity of this rule, but offer up the following anecdote which fully illustrates its insidiousness. I once managed to cut a length of crown molding one inch longer than marked, and laughed at this mildly embarrassing error until discovering the original measurement to be two inches too short. This was, of course, the molding meant for the shortest wall in the room, so the piece was a total loss. -Ed.

Because I am fully cognizant that these musings betray an obsessiveness that may not be healthy, it is with some trepidation that I post these final thoughts on hang angles. For those who weary of the topic, take comfort in my promise that this is the final post on the subject for the immediate future.

In a previous post, I mentioned in passing that cant has an effect on hang angles. Before examining this effect, let us define cant and enumerate some of its purported benefits. 

A canted saw is one whose toothline is not parallel to its spine. Invariably, the taper is such that the depth of cut is greater at the heel than at the toe. While some old saws have canted blades that are accidental byproducts of careless sharpening or rough handling, there is ample evidence that cant was an intentional feature on many early saws. While I know of no written evidence that shows early makers claimed any advantages for canted blades, modern writers and makers are not so silent. Four of the most commonly cited benefits are these:

1. By changing the angle at which the teeth attack the fibers of the wood, the saw cuts more smoothly.
2. By effectively raising the toe of the saw above the heel (at the toothline), the danger of cutting past the marked baseline on the backside of the board is lessened.
3. By removing some of the plate, the saw is lightened and the center of gravity is shifted towards the handle. This is further enhanced if the back, or spine, of the saw is also tapered (as is common on many canted saws of old).
4. It just looks cool. And it is nearly a universally accepted principle that, given two tools of identical functional quality, the one that looks better will almost always fare better in supposedly objective tests.

Before going further, let us first define three measurements. The first of these is cant, which we define as the angle formed between the toothline and the top of the spine. On an uncanted saw, this is 0 degrees. We call the second measurement secondary hang, and define it as the angle formed between the top of the spine and a line drawn perpendicular to the back of the handle. The last is primary hang, which we have heretofore simply called hang. In the trivial case of an uncanted saw, the primary and secondary hang angles are identical. The relationship between cant, primary hang, and secondary hang is shown in Figure 1, and is given by the equation:

secondary hang = primary hang – cant

Figure 1.  Showing how I measure cant, primary hang, and secondary hang.

To illustrate points 1 and 2, consider the uncanted saw in Figure 2, a typical twelve inch carcase saw with a primary hang angle of 33 degrees. The easiest way to add cant is by removing some of the metal at the toe of the blade. If we remove 1/2″, a cant of 2 degrees is introduced, increasing the primary hang angle of the saw to 35 degrees. The secondary hang angle remains unchanged.

Figure 2.  Top: Uncanted saw.  Bottom: Canted saw created by removing 1/2″ of blade from the toe.

Because the spine of a saw is so visually dominant while sawing, the natural inclination is to use it as a reference point when sawing, so it is reasonable to expect that both the canted and uncanted saws are held with their backs horizontal. This being so, the teeth of the canted saw are cutting with the grain rather than directly across it (Figures 3 and 4). While it certainly does not hurt, the benefit is is minor when ripping, and makes virtually no difference when cross-cutting. This covers the first of the reasons enumerated above.

Figure 3.  Top: Uncanted saw cutting a typical tenon cheek.  Bottom: Canted saw cutting a typical tenon cheek. In both cases, it is presupposed that the back is horizontal.

Figure 4.  Closeup of saws from Figure 3.

Further examination of Figure 4 reveals the rationale behind the second reason. When the saw teeth reach the baseline of the cut in the front of the workpiece, they have not yet reached the baseline on the back (which is not visible whilst sawing), reducing the risk of overshooting your mark. To reiterate an important point, this benefit depends on the premise that the back, or spine, is always horizontal.

In the scenario outlined above, the handle is unchanged in its relation to the spine of the saw (the secondary hang angle). This means that the sawyer’s positioning, stance, and hold on the saw can remain unchanged even while the primary hang angle increases. Since the primary hang angle has increased, the transfer of the applied force to the teeth is (slightly) affected. The effects of this are discussed in great detail in two previous posts: Concerning (primary) hang angles and saw handles and Further discussion of (primary) hang angles.

If canting is accomplished by pushing the toe end of the spine down on the blade (as often happens with folded spines), then the secondary hang angle is decreased, affecting the sawyer’s positioning, stance, and hold on the saw (refer to Concerning (primary) hang angles and saw handles for more detail). The primary hang angle is unchanged, so the transfer of the applied force to the teeth is unaffected.

It goes nearly without saying that cant may be introduced by endless combinations of changes to primary and secondary hang. Exploration of these borders on tedium and would only tax our patience. [Border? I think that line was crossed long ago. -Ed.] I would hope that sufficient knowledge can be gleaned from this and prior posts to enable puzzling out the varied effects.

The third cited reason, the reduction of weight, has the effect of reducing the downward force provided by the weight of the saw itself. This will make the saw feel somewhat less aggressive, as the teeth bite into the wood a little less. However, this is countered by the increased primary hang angle (assuming the first scenario outlined above) that directs more of the applied force downwards. The degree to which the two offset each other depends on the amount of cant and weight difference, and can be more fully explored in the post Further discussion of (primary) hang angles.

In practice, I find the first of these reasons to be practically negligible, the second to have some merit, and the value of the third to be dependent on the preferences of the sawyer. In short, canting has a negligible to minor effect on the mechanics of sawing.

This leaves the fourth reason, the sheer awesomeness of the canted look, which needs no further explanation.