Popular Woodworking 2006-10 № 157, страница 19

Regardless of what type of sawing you are doing, a saw's pitch is chosen according to the length of the kerf.

Rake: Leaning Forward or Back

Rake is the angle the front of the tooth makes with respect to an imaginary line drawn perpendicular to the saw's toothed edge. Forward swept teeth have negative rake. Teeth swept back have positive rake. A tooth that's perfectly perpendicular to the edge has zero rake. Rake, and not pitch, is chiefly what you are feeling when a saw cuts smoothly or is easy to start. In general, the less rake a saw has, the more aggressively it cuts. Saws with more rake cut more slowly but are easier to start and give you a smooth feel. If you are cutting very hard wood, a bit more rake makes the job more pleasant. But this same saw will cut softer woods more slowly. Choose rake based on the hardness of your stock. If you have trouble starting your cuts, choose a saw with more rake.

Fleam: The Bevel on the Tooth

Fleam is the angle filed on the front of a tooth with respect to the flat side of the saw. Generally speaking, saws with no fleam (that is, they are filed straight across) are called ripsaws. Saws with any amount of fleam are typically called "crosscut saws." (Please don't confuse handsaws filed with fleam for work across the grain with the long two-man timber saws that are also called "crosscut saws.")

PROGRESSIVE FILINGS

A really coarse ripsaw is a joy to use, but a pain to start. You can have an aggressive saw that starts every stroke easily without an iron wrist. The teeth can vary in pitch and rake along the length of the blade. This was common before machines cut sawteeth, and, contrary to popular belief, was absolutely deliberate. Disston varied the pitch on ripsaws such that a 4 tpi ripsaw may have as many as 7-8 tpi at the toe. It was common to vary rake angles as well. Modern saw filers are experimenting with progressive filings in which only rake varies. You could try varying only pitch. In short, there's no rule that says all a saw's teeth have to be the same. By varying the shape of the teeth along the edge of the saw you can further optimize the performance of your handsaws. — AC

Lots of folks know the pitch of their saws, but very few know how much rake they have. Rake makes a huge difference in how a saw feels and performs in different stock. When staring down a piece of ebony or lignum vitae, I'm likely to select a saw based more on its rake than pitch.

Any amount of fleam will greatly improve a saw's performance working across the grain. Too little fleam will cause the grain to "log roll" causing tearout. Too much fleam makes saw teeth weak. I think saws with too much fleam cut more slowly.

In addition to fleam, some amount of rake is required for a clean crosscut. You can experiment with different amounts of both. I prefer 20° of rake and 20° of fleam.

While fleam alone may define a crosscut saw, some contemporary sharpeners add tiny amounts of fleam to ripsaws. They report even less than 5° of fleam improves a saw's ability to make an occasional crosscut and may be a welcome addition when ripping hard woods.

Set: How Much the Tooth is Bent

Set refers to the amount a tooth is bent sideways (perpendicular to the broad face of the saw). Set allows the saw to lay a slit wider than the thickness of its blade. This reduces the friction of the blade in the slit and is supposed to reduce the effort of sawing. What set does not do is allow you to continue sawing when the stock closes up the slit. The solution to that problem is a wedge.

I'm a proponent of set, but not everyone agrees it's necessary. Some say saws without set lock into the kerf and will stay dead true and straight. My advice is to try a saw without set and see how you like it. I've not found it to be advantageous, but that doesn't mean you won't. Be gentle setting your sawteeth. Too much force can cause teeth to break and set is easy to add and very difficult to remove.

Fleam is the angle of the front of the saw's tooth. It helps make a smooth crosscut ... I think. See sidebar below.

IS FLEAM NECESSARY?

I've read and probably asked the question: At what angle to the grain is fleam necessary? Dovetails, for example, are often cut at 10° to 20° off the grain direction. Should these saws be fi led with fleam? I think the answer is "no." I don't think to pick up a crosscut saw until the angle is 45° or higher. But the larger question of whether fleam is necessary is more difficult to answer. Colonial Williamsburg's Anthony Hay Cabinet Shop has no saws with fleam. The scholars there have uncovered no evidence that 18th-century saw makers filed fleam, so they have chosen to work without it. They do however, routinely knife all crosscuts. I have noticed that all of their saws seem to have a bit more rake than their modern counterparts. They also seem to link pitch and rake, i.e. they file more rake on higher pitched saws. Unfortunately, there aren't many woodworkers relying solely on handsaws for all their cuts. So I think Arts & Mysteries readers should try some experiments of their own. Can you crosscut with a ripsaw? How much rake is enough to make this job comfortable? Try it yourself and report back. — AC

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