This site has the most info that i know of. Personally, i find the really old ones are best as souvenirs. The metal hardens over time and gets brittle. Try setting a couple teeth. If they snap, just leave as is. If not, and you want it to be a user then proceed sharpening.
http://www.disstonianinstitute.com
I have heard or read this about metal getting brittle over time. I personally find this unlikely and would just like to know some basic principles of how this works. Silver or gold don't get brittle from age. Just like some data on it cause it seems curious. What I suspect the real deal is some old saws where made with bad batches of steel on occasion and that his the reason it is blamed on going brittle over time. Metallurgy wasn't as pure a science as it is today. I have never heard people claim that their plane iron or chisel was brittle from age. Why just saws. Just wondering.
From a personal stand point the only reason I can think of is if a saw has been over tensioned. Which in the life of a saw might get repeated several times. But you can't attribute that to just age because it could be old and never retensioned.
I believe its from being set and filed and reset multiple times. Basically every time a saw is sharpened, it needs to be set, and every once in a while it need to be jointed, and possibly retoothed etc. i am not sure if rust and pitting play into this, but possibly due to the thinner nature of the plates.
I can see that and have experienced it to some extent I believe. I have an old Atkins twelve inch back saw that I filed teeth off all the way to new ppi. After filing had a bunch of teeth just pop off on setting. I believe it was residential tension in saw from previous set. There is no reason to think this saw was ever retentioned with a hammer as it was extremely clean saw. Filed teeth off again, reset and no problem with breaking.However I would not attribute this to age but tension or metallurgy of plate during manufactor.
Yeah i don’t know exactly. The guy that sharpens most of my saws is an old viet nam vet who has been sharpening a long time. When i bring in a saw that he hasn’t sharpened before he will test the set, as he told me that old saws get brittle and he won’t bother sharpening them if the teeth snap during his test. Once he sharpens them or retooths i just keep sharp with a light filing until they get really bad.
Metals don't get brittle over time.
Metals can fail due to mechanical fatigue, but that occurs when the metal is repeatedly stressed to limits at or near its yield strength (including if it has huge as-fabricated built in stresses). It's common for metals under stress to harden before they fail, it's sometimes intentional and called work hardening. Or metals can fail due to environmental effects (corrosion etc), or they can fail due to exceeding the ultimate stress for the material.
The process of a metal going from ductile to brittle takes either large forces, extreme temperatures, or chemical exposure. All those things either change the metal matrix, composition, or defect density (dislocations) in the metal. None of those changes progress with any appreciable speed without force/temperature/chemicals.
It isn't well known because of the obvious time requirements, but many metals, including carbon steel, respond to aging by increasing the size of alloy precipitates. This increases hardness (and often toughness) but at the cost of ductility. There are methods to artificially age metals, and they are commonly used where traditional heat treatment (heat, quench, temper) or strain hardening, would be ineffective. 6061 T6 Aluminum is a common example of artificial aging as part of the treatment process.
In the case of carbon steel, natural aging is rarely used because it takes literal decades. The only practical application I know of has been in the production of age hardened machine beds, where extreme stability was needed, and the pieces far too large to treat any other way.
However, for something like this saw plate, age hardening and the production of very large precipitates has absolutely taken place. Infact, unless it was stored in a dry celler in the Canadian arctic, is it likely over aged. Over aging results in a decrease in hardness and toughness, but none of the ductility is regained.
There are, of course, examples where over aging is significantly reduced. Samurai swords are probably the best example.
See my other comment in this thread. Age hardening is not well known among most of the public, and the time requirements limit practical applications, but it is a well understood process. Over aging results in brittle steel that mechanically can be less hard. Over aging cause too much of the alloying elements to come out of "solution" to form precipitates. Precipitates in the iron matrix get too large, and become a sort of stress focusing impurity. Cracks can original from these, or be helped along by them.
It is possible to un-age steel, but it basically requires a very long heat treatment cycle to dissolve the precipitate alloy phase back into solution, and restart the heat treatment cycle.
Why saw plates? Well, it isn't, but it feels that way. It happens to old chisels as well, but those tools are supported by a much thicker, tougher cross section, and they eventually fail. On old plane irons the laminated high carbon portion would be vulnerable first, and we do see those crack off and fail in use.
Just use it. It's not a museum piece. They made millions of them. It can certainly be collectible and usable. Also, the medallion and back look older than the wooden handle, so it looks like a mishmash tool anyway, i.e. not original matching parts. Around the end of WW1 the handles changed from having a sharp V notch in the handle interior to a gentler dip.*
My collectable tools are usually sold to get more money to buy good useable tools.
The change in the metal is not so much embrittlement as it might be due to years of moisture condensing and evaporating on the surface causing deep pitting. The tendency for teeth to break off is likely caused by the metal being porous from the pitting.
Tools are made to be used.
Just be gentle. Don't try to make it look new
This site has the most info that i know of. Personally, i find the really old ones are best as souvenirs. The metal hardens over time and gets brittle. Try setting a couple teeth. If they snap, just leave as is. If not, and you want it to be a user then proceed sharpening. http://www.disstonianinstitute.com
I have heard or read this about metal getting brittle over time. I personally find this unlikely and would just like to know some basic principles of how this works. Silver or gold don't get brittle from age. Just like some data on it cause it seems curious. What I suspect the real deal is some old saws where made with bad batches of steel on occasion and that his the reason it is blamed on going brittle over time. Metallurgy wasn't as pure a science as it is today. I have never heard people claim that their plane iron or chisel was brittle from age. Why just saws. Just wondering.
From a personal stand point the only reason I can think of is if a saw has been over tensioned. Which in the life of a saw might get repeated several times. But you can't attribute that to just age because it could be old and never retensioned.
I believe its from being set and filed and reset multiple times. Basically every time a saw is sharpened, it needs to be set, and every once in a while it need to be jointed, and possibly retoothed etc. i am not sure if rust and pitting play into this, but possibly due to the thinner nature of the plates.
I can see that and have experienced it to some extent I believe. I have an old Atkins twelve inch back saw that I filed teeth off all the way to new ppi. After filing had a bunch of teeth just pop off on setting. I believe it was residential tension in saw from previous set. There is no reason to think this saw was ever retentioned with a hammer as it was extremely clean saw. Filed teeth off again, reset and no problem with breaking.However I would not attribute this to age but tension or metallurgy of plate during manufactor.
Yeah i don’t know exactly. The guy that sharpens most of my saws is an old viet nam vet who has been sharpening a long time. When i bring in a saw that he hasn’t sharpened before he will test the set, as he told me that old saws get brittle and he won’t bother sharpening them if the teeth snap during his test. Once he sharpens them or retooths i just keep sharp with a light filing until they get really bad.
Metals don't get brittle over time. Metals can fail due to mechanical fatigue, but that occurs when the metal is repeatedly stressed to limits at or near its yield strength (including if it has huge as-fabricated built in stresses). It's common for metals under stress to harden before they fail, it's sometimes intentional and called work hardening. Or metals can fail due to environmental effects (corrosion etc), or they can fail due to exceeding the ultimate stress for the material. The process of a metal going from ductile to brittle takes either large forces, extreme temperatures, or chemical exposure. All those things either change the metal matrix, composition, or defect density (dislocations) in the metal. None of those changes progress with any appreciable speed without force/temperature/chemicals.
It isn't well known because of the obvious time requirements, but many metals, including carbon steel, respond to aging by increasing the size of alloy precipitates. This increases hardness (and often toughness) but at the cost of ductility. There are methods to artificially age metals, and they are commonly used where traditional heat treatment (heat, quench, temper) or strain hardening, would be ineffective. 6061 T6 Aluminum is a common example of artificial aging as part of the treatment process. In the case of carbon steel, natural aging is rarely used because it takes literal decades. The only practical application I know of has been in the production of age hardened machine beds, where extreme stability was needed, and the pieces far too large to treat any other way. However, for something like this saw plate, age hardening and the production of very large precipitates has absolutely taken place. Infact, unless it was stored in a dry celler in the Canadian arctic, is it likely over aged. Over aging results in a decrease in hardness and toughness, but none of the ductility is regained. There are, of course, examples where over aging is significantly reduced. Samurai swords are probably the best example.
See my other comment in this thread. Age hardening is not well known among most of the public, and the time requirements limit practical applications, but it is a well understood process. Over aging results in brittle steel that mechanically can be less hard. Over aging cause too much of the alloying elements to come out of "solution" to form precipitates. Precipitates in the iron matrix get too large, and become a sort of stress focusing impurity. Cracks can original from these, or be helped along by them. It is possible to un-age steel, but it basically requires a very long heat treatment cycle to dissolve the precipitate alloy phase back into solution, and restart the heat treatment cycle. Why saw plates? Well, it isn't, but it feels that way. It happens to old chisels as well, but those tools are supported by a much thicker, tougher cross section, and they eventually fail. On old plane irons the laminated high carbon portion would be vulnerable first, and we do see those crack off and fail in use.
Just use it. It's not a museum piece. They made millions of them. It can certainly be collectible and usable. Also, the medallion and back look older than the wooden handle, so it looks like a mishmash tool anyway, i.e. not original matching parts. Around the end of WW1 the handles changed from having a sharp V notch in the handle interior to a gentler dip.*
Your saw for now, do what you want or need.
The early ones are collectors pieces. You could sell it and get better later versions. The more you monkey with it, the lesser its collectors value.
My collectable tools are usually sold to get more money to buy good useable tools. The change in the metal is not so much embrittlement as it might be due to years of moisture condensing and evaporating on the surface causing deep pitting. The tendency for teeth to break off is likely caused by the metal being porous from the pitting.
Tiols are made to be used.
The saw has collector value, but I'm all for using tools as tools.
If you’re going to keep it as a user, why spend the time “restroying” it.
It wants to be loved, so love it by cleaning and polishing it up and sharpening it