Why do big cross-cut saws have 'bellies'?

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Why do big cross-cut saws have 'bellies'?

Postby Brian Williamson » Fri Jan 25, 2013 9:51 am

This is a topic that is being debated on the American Cross-cut forum. Along with the supplementary question of when did such bellies first appear?

Despite the fact that they have a large and active cross-cutting community over there, there has been no consensus as to why they evolved or when.

I won't muddy the waters here by offering up any of their suggestions, rather leave it to you to produce your own theories. I will just note that not only do the big two-man saws have bellies (or breasted toothlines), but the smaller, one-man saws do as well. And breasted tooth lines were not uncommon on top quality carpenters hand/panel saws, though I'm not sure you'll fine any being made like that today.

The date they appeared ought to be easier to pin down. They are universal in saw catalogues of the 1860's and '70's, whereas mediaeval pictures (apparently) all show them as straight edged saws.

So, does anyone know of any mediaeval pictures showing bellied saws? Does anyone have pictures from tool catalogues in the first half of the 1800's showing both straight and bellied saws? Or either by themselves.

It is probable that european manufacturers were predating the big american producers. Disston, for example, didn't start up till around 1850, whereas Peugeot were mass-producing saws in 1810 in France. And have had a continuous history of tool-making, so possibly have archive collections of old saws/pictures/ catalogues.

Page from 1880 Spear and jackson catalogoe.

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Re: Why do big cross-cut saws have 'bellies'?

Postby TonyH » Fri Jan 25, 2013 11:08 am

Thomas Flinn still make saws with a breasted tooth line - their Pax brand notably, and their one and two man crosscut saws. According to them :

"these saws are taper ground and breasted (meaning less teeth are in contact with the wood and therefore less friction)"

Though I can't quite get my head around how you can reduce the friction without reducing the cutting action.
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Re: Why do big cross-cut saws have 'bellies'?

Postby Billman » Fri Jan 25, 2013 6:06 pm

A bellied saw should keep the teeth on contact with the wood better, allow more efficient removal of the saw dust as well as the rocking motion allowing the whole body to be used, not just the arms - all round more efficient and less tiring????
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Re: Why do big cross-cut saws have 'bellies'?

Postby Billman » Fri Jan 25, 2013 6:14 pm

Just check both Grimshaw's and Disston's books on saws - they do not mention it (note both books can be downloaded as PDF files from Google Books).. Most early saws have a thin straight blade held under tension in a wooden frame - a type that survives in Europe until this day. It was only with the advent of reliable thin sheet steel, i.e. post Huntsman c 1740 and his development of crucible steel, and the rolling mill for steel (those for lead/copper/silver date from about 1759) by Henry Cort c 1783, that the modern thin sheet saw blade could be made... Prior to that date saws were made of hammered steel – in the Spear & Jackson history, also downloadable as a PDF file, there are images of carpenters’ saws dating from the mid 18th century, and an illustration from the Bedford Book of Hours (produced for the wedding of John Duke of Bedford to Ann of Burgundy in May 1423) showing a carpenter helping Noah to build the Ark using a curved hand saw (in the foreground is a more common frame saw)

(Note: I tried to edit this post a fews minutes after I posted it - was locked out of the site for nearly a week, so I have just edited it for future readers...)
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Re: Why do big cross-cut saws have 'bellies'?

Postby Billman » Fri Jan 25, 2013 6:32 pm

Just looked at the posts on the crosscut saw forum - while doing so the thought came that with concave blade cutting on a round log the actual cut would start better as the saw rides up the log at the start and down the log at the end - thus creating a longer starting cut than the tangential one produced by a straight blade. Thus you would get a curved cutting surface, hence more teeth in contact, and faster cutting.... see sketch....

Saw starts on the flank, at position 1 it is into the cut - cutting surface is curved. At 2 over half way, curved cutting surface is 50% longer than the straight line... Now we need to actually try one, stop half way, and then cut about 6mm away all the way through and break off the thin section to see what shape the cut really is - over to someone with a sharp saw and younger muscles than me....

What made me think of this was the memory of days of bench filing when teaching metal work, where when filing a curve you rock the file away from the curve, not towards it.....
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Re: Why do big cross-cut saws have 'bellies'?

Postby gavin » Fri Jan 25, 2013 10:13 pm

Billman,
On the face of it your idea & diagram makes sense if the saw rides UP and then down i.e if the kerf-bottom is correspondingly convex. BUT: Have you ever seen such a convex kerf-bottom? I have not. They are either flat or slightly convex.
For this reason, I think your analysis incorrect. But do tell me if you think I have missed something!
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Re: Why do big cross-cut saws have 'bellies'?

Postby jrccaim » Sun Jan 27, 2013 6:43 am

Japanese log saws have no belly. To my mind (I have used both) the straight blade cuts just as well as the bowed one. Just my opinion, and I do have a bias toward Japanese tools. Once upon a time American saws had no bellies either. Look at older 17th century saws. No belly there. There is a fad thing going on here. Some manufacturer produced a curved saw and sold everyone on it.So it got to be tradition. The advantage of a curved saw, as Billman points out, is that it might be easier to start (or even push through) because fewer teeth are in contact with the wood. Maybe so. Certainly starting is a big point. On the whole I find no difference between them. Except I like Japanese saws! Fads happen today. Procter & Gamble made bazillions of Pounds off "Crisco" (lard substitute) because they did a very clever marketing campaign, and convinced everyone that it was good for you. In fact it's not, it is hyrdrogenated coconut oil (the "co" in Crisco) and very bad for you indeed. So there is an awful lot of fad stuff going around, aided by marketing types and ad agencies. And it was just that way in the 18th century too.

That said, I think there is also an awful lot of "this is what I am used to" going around too. You get used to something e.g. a western saw. You pick up a Japanese saw and it seems unusable. What, cut on pull? Crazy stuff! Deranged orientals! :) But once you get used to it there is no comparison. So I do not think this is physics. I think it is habit instead.
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Re: Why do big cross-cut saws have 'bellies'?

Postby Brian Williamson » Sun Jan 27, 2013 9:39 am

jrccaim wrote:There is a fad thing going on here. Some manufacturer produced a curved saw and sold everyone on it.So it got to be tradition.



That's a really interesting notion, jrccaim. Certainly it has parallels in the tool world.

Take axes - straight handles or curved handles? Some say yes, some say no.

Look at billhooks in this country - enough different patterns even in the 20th century to start a small war. And you can probably boil them all down to three basic types.

maybe the industrial revolution simply made it easier for people to experiment, and if it caught on they stayed with it. Afterall, if you had to laboriously make every saw by hand, you'd have to be pretty convinced of it's potential to try a different pattern.

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Re: Why do big cross-cut saws have 'bellies'?

Postby Shankar » Sun Jan 27, 2013 10:45 am

I think the principal is similar to that of swords where a curved sword (Japanese) is a much superior slashing weapon than a straight (Medieval European.) Only a small part of the blade is biting at any one point whilst the rest are being cleared of sawdust this also makes the saw easier to pull and much more effective at cutting. If there is lots of power this is less of an issue like in a chainsaw. The curved edge is also a longer edge (for the same length of saw) to pull through the wood. The same can be said of the GB carving axe vs straight edge axe, the former is for slicing the other chopping.

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Re: Why do big cross-cut saws have 'bellies'?

Postby Davie Crockett » Mon Jan 28, 2013 3:21 pm

I have a theory...that the bowed saw when in use, exerts the most pressure on individual teeth as they go through the cut. Downward pressure and forward motion on one tooth will cut deeper than the same motion and pressure over several teeth at the same time.

As the saw is pulled back and forth the trailing edge leaves a kerf with its bottom pointing up towards the other side. It is then easier for the returning stroke to remove this triangular section and then leave the same shape on the opposite side.

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Re: Why do big cross-cut saws have 'bellies'?

Postby Billman » Mon Jan 28, 2013 7:42 pm

Racing saws have little or no belly, but very thin and long teeth - they are pulled almost horizontally - I guess much depends on the stance and movement of the pair of sawyers as to how the bellied saw cuts - are they pulled horizontally, or does each man pull them up (or down) slightly??

And are felling saws better if slightly bellied???
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Re: Why do big cross-cut saws have 'bellies'?

Postby Billman » Mon Jan 28, 2013 8:04 pm

Just had another look at images of cross cutting logs in the woods - and I think I may have cracked it... Most cross cutting (known as bucking) was done with the log on the ground, after the tree had been felled. It needed to be cut into shorter lengths in order to move it. A bellied blade stops the ends of the saw from digging into the ground, especially at the end of the cut, when the saw is nearly through....
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Re: Why do big cross-cut saws have 'bellies'?

Postby mrcharly » Mon Mar 11, 2013 3:08 pm

It could also be to keep a more consistent point of contact. As each 'sawyer' switches from 'push' to pull, they will rock the saw slightly. If the blade was straight, even a small angle of rock would completely change the contact point in the log. A curved blade will cut more consistently. this is hard to explain without pictures.
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