Why Crested HandSaw Blades?

[Eric Brown]

My question is about crested handsaw blades. I have seen four basic types of handsaws with crested blades. Very long loggers saws. Long handsaws primarily for ripping.
Short saws for flooring. Veneer saws. So why not other types of saws?
At first you might say that dovetail saws should cut a flat groove, but then I recall how some people undercut their dovetails, in which case a curved cut might facillitate them better. So why not crested dovetail saws? Not sure if sliding dovetails would benefit, but not sure they wouldn't either.

As an extra question, how do you determine how much crest and what is the easiest way to make or keep a crest when sharpening?

Sorry all. I really did mean "Breasted" instead of Crested

Any and all comments welcome.
Thanks. Eric

[Peter Evans]

Handsaws are historically "breasted", the longer they are the more breasting. Look at how you cut with a 26" saw (on a saw bench) - there is a curve in the motion of your arm. For backsaws, the action is not long enough for breasting; and in any case as they are used at the bench, the action is straighter.

[Johnny Kleso]

I'm guessing it opens up the gullets so saw dust can fall out more easy..
Also makes the saw cut more agressive..

[Jim Koepke]

One question can lead to many more.

Mine would be what does it do to the rake angle if anything?

Could it be a difference of a degree or two?

jtk

[Marv Werner]

Jim,

Most saw filers don't control their rake angle exactly, so when filing a breasted or crowned saw, the rake will vary just a bit, depending on how much it is breasted, but it won't be noticeable anymore than the varying rake angle that is normally filed.

[Marv Werner]

You can maintain the breasted curve in the tooth edge when you do the jointing just prior to filing. The amount varies a lot from saw to saw. Some of the old saws were breasted as much as 3/8". It was done on the higher end saws, and not on the cheaper ones.

[Ray Gardiner]

Hi All,

Mike Wenzloff did a write-up here.. http://www.wenzloffandsons.com/faq/31-general/51-breasting.html that explains it well.

As he says in that article, "There is a lot going on in the simple design of a hand saw"

Regards
Ray

[Chris Vandiver]

I'm guessing it opens up the gullets so saw dust can fall out more easy..
Also makes the saw cut more agressive..
That is pretty close to why some saws are breasted.


With a breasted saw, there is always a fresh tooth/gullet in the cut. The curved tooth line helps to clean out sawdust more easily than a straight tooth line. The big rip saws often have 3/8"+ of breasting(just as Marv pointed out) to help them rip faster.

I don't believe breasting has anything to do with arm motion. That seems to me to be an "old wives tale".

[Adam Cherubini]

My question is about crested handsaw blades. I have seen four basic types of handsaws with crested blades. Very long loggers saws. Long handsaws primarily for ripping. Short saws for flooring. Veneer saws.


Eric,

I agree with Mike. I think saws and sawing are complicated. I'm sorry I don't have the answer. I can say this tho:

Veneer saws and flooring saws are designed for entry work. So they are curved for a definable and different reason than logging saws.

The logging and rip saw could be breasted so that as you push the saw in a straight line, the curved blade compensates for the wood you are taking away. This would explain why a 2 man whip saw (cross cut logging saw) is shaped like a smile. Of course, when you see guys using one of these, they are using a circular stroke. So maybe it is just a natural stroke sort of thing.

I don't think saw dust ejection has anything to do with it. All saws have this concern and no other saws are typically bellied.

I have made and used saws with it and without it. I much prefer rip saws with a bit of belly. 1/2" isn't too much, but isn't typical. You file the bellly before you start filing the teeth. You joint it in. While you are filing the teeth, you can forget about the belly. Rake is measured from the tangency at a given tooth. In reality, when I am sharpening a saw, I may focusing on only a single tooth, or I'm looking at the one before it and the one after it, so I really don't get a sense for the curve.

Good question. Sorry i don't have a better answer.

Adam

[Eric Brown]

So far a lot of interesting ideas about Breasted saws. If Mike (and others) are right about it compensating for arm motion, then the "perfect" saw would also need to take into consideration the users arm length. Wouldn't it?

In my limited exposure, I have never heard of a Breasted mitre box saw. Maybe because
the human arm mechanics are different then?

I also haven't heard of a Breasted bow saw.

I believe some, but not all the Japanese pull saws are breasted.

Somebody should do some experiments or something.
Hard data and not just speculation about why.

Ergonomics study challenge for a college or something?
Anyone up to the challange?

Thanks. Eric

[jamie shard]

With a breasted saw, there is always a fresh tooth/gullet in the cut. The curved tooth line helps to clean out sawdust more easily than a straight tooth line.

It would also concentrate the force over fewer teeth... ???

[David Weaver]

My simple answer would be, because it makes the saw nicer to use - especially in a nice long ripsaw. Probably for the reason Chris mentions, it does a very subtle job of presenting the saw to the wood in a way that it works nicer.

The reasoning for veneer saws is different, though - more scoring and slicing from the top surface of the workpiece rather than ripping - the use is different.

So, anyway, regardless what the argument is about historic this or that or phsyiology, the only thing that matters to you as a user is that it will probably be a more pleasant saw to use.

[Jim Koepke]

Hi All,

Mike Wenzloff did a write-up here.. http://www.wenzloffandsons.com/faq/31-general/51-breasting.html that explains it well.

As he says in that article, "There is a lot going on in the simple design of a hand saw"

Regards
Ray

Well, that answers one of my questions:


(From the page linked by Ray) Tooth geometry on a straight toothline remains fairly static along the entire length (excepting progressive raked saws). This means the first tooth and the last tooth will have the same rake. While a breasted saw has the same physical static tooth geometry, breasting alters the rake while sawing. Along the toothline, the toe will be a greater rake than at the heel…

interesting information, have to look around that site a bit before working on my next saw.

jtk

[Jim Koepke]

In my limited exposure, I have never heard of a Breasted mitre box saw. Maybe because the human arm mechanics are different then?

Most of the time in my use of mitre box saws, dove tail saws and tenon saws they are operated almost flat for a somewhat short, precise cut. A breasted saw might be more of a hindrance than a help in such situations. If the saw was not able to "rock" while cutting, then only a few teeth would be doing all the work.

This makes me think the curved tooth line being longer than a straight tooth line will have a few more teeth. One may think, "Big deal, two maybe three more teeth." But if one is cutting a lot of wood, after 100 strokes this will be 200 or 300 more teeth helping in the cut.

I am sure back in the day if a workman could rip a plank just a bit faster it brought him favor on the job.

jtk

[Jim Koepke]

I also haven't heard of a Breasted bow saw.

Maybe we can introduce a new line of breasted coping and fret saws.:confused::cool::D

jtk

[David Weaver]

I also haven't heard of a Breasted bow saw.

I believe some, but not all the Japanese pull saws are breasted.


I think a breasted bow saw blade would wander. I'll wait for someone else to go through the trouble of hacking up one of their wonderful breasted panel saws to make a breasted bow saw blade. The only one I have works very well with a straight blade.

I have two japanese crosscut saws that are breasted, but the breasting is drastic on them (they are @300 style Z-saw brand). They are aggressive cutters in crosscut and still leave a better finish than most of my western saws (they are not as fast as a fine finish 26" long 12 tpi panel saw, though, but they are fast for a japanese saw).

If you look at japanese log saws (maebiki), they are not breasted. I would've guessed negative breasting would help a little on them, but it makes sense you wouldn't want that unless you were cutting lumber and something not the full thickness of the log. Look at how aggressive the teeth are on these:

http://japantool-iida.com/saw/2008/05/maebiki-saw-by-isaburo.html

The saw pictured has about one tooth per inch near the back end of the cut (progressive tooth size, just like older american saws)

A miter box, on the other hand, would have issues if the toothline was breasted unless there was a sacrificial board fairly thick under it. If you've used miter boxes much, they aren't exactly optimal cutting machines if you are used to using a full stroke on a panel saw. They do what they're intended for (cut at fixed positions), but the short stroke limits you to being a little robotic - you can cut faster with a panel saw. The guides also functionally keep you from doing the same type of stroke that breasting would help, anyway. They do move up and down, but not always that well when there's tension on them.

[Jonathan McCullough]

It would also concentrate the force over fewer teeth... ???

That is exactly correct. Breasting in hand saws doesn't have anything to do with natural arm motion or sawdust removal. The theory is that fewer teeth in continuous contact with the wood at any given time will reduce the friction, and hence the effort, in sawing. Theoretically, with a breasted saw blade only one tooth is in contact with, and cutting, the wood at any given time throughout the stroke, whereas with a straight line of teeth, *all* of the teeth within the cut are in contact with the wood at any given time. If you're cutting through something small with a crosscut back saw, the amount of friction is negligible. If you're cutting through something as thick as a log however, the friction created by having every single tooth within the cut dragging along the cut can be considerable. So you get "misery whips" and crosscut log saws with a lot of breasting or "belly."

In practice, the line cut by a breasted saw (as viewed from the side) conforms to the crescent shape of the saw, so the end of every stroke becomes more difficult as more teeth come into contact with the wood. To compensate, a pair of crosscutting sawyers can rock the saw handles up and down with each stroke to compensate, so that fewer teeth are exposed at either end of the cut.

A 28-inch rip saw should be breasted by virtue of the fact that, even when you're ripping through something as thin as the 2-inch section of a 2 x 4, the length of the section of teeth exposed to the wood in the cut can often be five or more inches long. Think about it: You're ripping a 2 x 4 into two 2 x 2 sections. It's on a saw bench and as you make your saw stroke more horizontal, you're cutting through a longer cross section of wood. Sawing at 45 degrees, the length of wood exposed to the tooth line is about 3.5 inches. If you dip the saw handle down lower to establish a shallow groove for subsequent power strokes, the length of wood exposed to the tooth line could be five inches. Cutting through even thicker pieces of wood would be more dramatic.

Veneer saws are different. It's intuitively more maneuverable to use a smaller, rounded section of saw than to struggle with the sharp corners of, say, a dovetail-like saw digging in at the beginning of every stroke.