Thread: Help with a Dodo (Disston 77)

Originally Posted by Fergiz01

...... There's probably a good reason why these never went on to replace regular back saws, however it's good to know the advantages and disadvantages....

Zac, as discussed in this & other threads, I guess we can only speculate on the reasons why tapered backsaws never swept the world. I would suggest, as others have, that the first hurdle would have been the cost/perceived benefit ratio. For those who did buy them, some would have looked after them & been able to take advantage of their clean-cutting abilities, the less-diligent would have run into bother pretty quickly, I suspect. It would seem you must follow Disston's instructions on those fleam angles, or you create a dog of a saw. Given that a very fine cut surface isn't of paramount importance in a majority of situations, & they require a little extra fussing to maintain their advantage over 'set' saws, I can see how they just wouldn't be appreciated in many workshops. So, few repeat customers, plus few enthusiasts talking them up = poor sales, & that would have been death to a product then just as it is now..

Whatever, I think you got yourself a bit of a bargain. This is a very nice saw, and should give you much pleasure & good service if you treat it well. It's a slightly larger saw than I prefer for everyday cabinet joinery, but I found it very comfy & intuitive to use. I reckon you could grow to like it very much, & it should handle all but the most delicate sawing tasks with great aplomb.

Couple of things I meant to mention about it before. Something not talked up in any of the discussions of 'no set' saws that I've seen, but quickly discovered with this one, is how easy it is to start your cut very precisely. Without set teeth to confuse your eye & make the saw wiggle slightly, it's a doddle to start this saw exactly where you want it - you can 'split the line' with it, with ease.

And I have a theory about why the 'extreme' fleam angle works to make the saw cut more freely, but I thought I'd canvass the collective wisdom to see if anyone else has any suggestions?

Originally Posted by Fergiz01

......I hope that you had fun!....

More than should be legal, Zac!.....
Cheers,

Originally Posted by IanW

And I have a theory about why the 'extreme' fleam angle works to make the saw cut more freely, but I thought I'd canvass the collective wisdom to see if anyone else has any suggestions?

Could it be because the extra angle compresses the cut material towards the center of the cut where it's less likely to bind between the saw plate and the side of the kerf?

Ray

You could be on the money with that, but could it also be even more simple? Sometimes to visualise what is really happening in practice I consider an extreme example. If you take a rip tooth filed without any fleam whatsoever I can imagine the sawdust packing into the gullet. As the saw exits the cut the sawdust falls as it is no longer "trapped" by the kerf and the gullet. Perhaps with a 45 deg fleam the sawdust is less likely to hang up. and not fall free.

Having said that (here we go says Ian) this might only affect the speed and efficiency of cutting rather than contributing to the jamming of the saw plate.

It is interesting that the No.77s used conventional filing geometry compared to the 120 ACME (what does "ACME" stand for by the way?), which had a tall tooth and was filed using a cant file with a smooth back. In other words only the face of the tooth was filed.

I did also notice that the No.77 on the Disstonian website was courtesy of backsaw.net

Regards
Paul

Originally Posted by Bushmiller

Ray
I did also notice that the No.77 on the Disstonian website was courtesy of backsaw.net

I'm inclined to try and find it, ( it's around here somewhere ) and try some high fleam angles. Trouble is, I've got too many other things to finish first.

Originally Posted by RayG

Could it be because the extra angle compresses the cut material towards the center of the cut where it's less likely to bind between the saw plate and the side of the kerf?

Ray, I'm not sure how you figure there is more compression with the 45 deg fleam? The teeth are actually thinner, so to my mind there ought to be less compression of the centre material.

OK, I'll put up my theory. I think there are two things going on. First, & perhaps most importantly, the leading edges of the 45 deg teeth are "sharper" and so they slice the wood fibres more cleanly. 'Blunter' teeth (i.e. with 20-25 deg fleam), bludgeon their way through the wood & smash the fibres apart, leaving lots of tiny dags in their wake. This would provide a good source of drag on the saw, whereas the smooth surface left by the 45 angles is causing less friction.
Second, because of the fleam angle, the leading edge of the tooth is being forced outwards by the wood as the saw moves forward. This would cause some flexing of the teeth, thus cutting a slightly wider kerf than the sawplate width. This would also apply to the blunter fleam angle, but the tips of these 45 teeth are very thin, which possibly allows more outward flexing.

Dammit, curiosity got the better of me, so today I put everything else aside and made a new saw. This saw is almost identical to the one I was using yesterday: Saws cf.jpg

Except that this saw has a few extra details on its handle & a slightly lower hang angle (part of another idea I had): 12tpi 45 fl.jpg
and, the teeth are filed 45 degrees with no set.

Well, it works almost as well as the 77. The pic isn't as clear as it could be, but I think you can see the lines on the right vs a smooth cut on the Test cuts II.jpg

I am simply flabbergasted that fleam angle can make such a difference! There's possibly a little more resistance when it gets deep into a cut, but it isn't nearly as much as I expected.

Ok, gotta scoot, we'll take this up later....

Originally Posted by IanW

Ray, I'm not sure how you figure there is more compression with the 45 deg fleam? The teeth are actually thinner, so to my mind there ought to be less compression of the centre material.

OK, I'll put up my theory. I think there are two things going on. First, & perhaps most importantly, the leading edges of the 45 deg teeth are "sharper" and so they slice the wood fibres more cleanly. 'Blunter' teeth (i.e. with 20-25 deg fleam), bludgeon their way through the wood & smash the fibres apart, leaving lots of tiny dags in their wake. This would provide a good source of drag on the saw, whereas the smooth surface left by the 45 angles is causing less friction.
Second, because of the fleam angle, the leading edge of the tooth is being forced outwards by the wood as the saw moves forward. This would cause some flexing of the teeth, thus cutting a slightly wider kerf than the sawplate width. This would also apply to the blunter fleam angle, but the tips of these 45 teeth are very thin, which possibly allows more outward flexing.

Dammit, curiosity got the better of me, so today I put everything else aside and made a new saw. This saw is almost identical to the one I was using yesterday: Saws cf.jpg

Except that this saw has a few extra details on its handle & a slightly lower hang angle (part of another idea I had): 12tpi 45 fl.jpg
and, the teeth are filed 45 degrees with no set.

Well, it works almost as well as the 77. The pic isn't as clear as it could be, but I think you can see the lines on the right vs a smooth cut on the Test cuts II.jpg

I am simply flabbergasted that fleam angle can make such a difference! There's possibly a little more resistance when it gets deep into a cut, but it isn't nearly as much as I expected.

Ok, gotta scoot, we'll take this up later....

I'm blatantly hi jacking this thread very temporarily.
My humble apologies Zac
Mr Ian is that some creative metal work I'm seeing.
I'm very impressed.
As you were

Originally Posted by Simplicity

.......is that some creative metal work I'm seeing.....

Not very creative, Matt. Apart from my usual chamfers (wide on the bottom small on the top), there's a curve on the toe of the spine to match the curve of the blade and a lamb's tongue just in front of the cheeks. About 2 minutes work with a couple of files.
Some day I'll get some engraving tools, then I'll try to be creative....

Cheers,

Originally Posted by Bushmiller

........ (what does "ACME" stand for by the way?).....

acme ˈakmi/
noun
noun: acme; plural noun: acmes

the point at which something is at its best or most highly developed.

The Acme saws may have been held out to be the best but the steel is more consistent in the No. 12's.

Originally Posted by IanW

Ray, I'm not sure how you figure there is more compression with the 45 deg fleam? The teeth are actually thinner, so to my mind there ought to be less compression of the centre material.

No, with the higher angle there is more compression toward the center of the kerf, moving material away from the cutting edge.

Whether that's the explanation for the reduced friction or not, I don't know.

Ray

Maybe the 45^o tooth slices the fibers better leaving a flatter surface than does a lesser angle which may leave fibers protruding from the cut face which impede passage of the saw plate. I have a couple of older references suggesting 45^o as the proper angle for filing saws.

A sharp saw isn't really that sharp when compared to a chisel or plane blade, it's more like an axe than a scalpel.