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  1. #16
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    Default sharpening

    Just another thought...perhaps saw plate hardness was limited by the need to be able to sharpen the saw in service by the user with a hand file. I'm unsure of what that limit (on Rc scale) might be.

    Regards,
    John

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  3. #17
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    Quote Originally Posted by jcge View Post
    Just another thought...perhaps saw plate hardness was limited by the need to be able to sharpen the saw in service by the user with a hand file. I'm unsure of what that limit (on Rc scale) might be.

    Regards,
    John
    A difference in RC hardness of around 10 is needed between the file and the metal being filed to easily file the metal and not rapidly ruin the file.

    The hardness is also limited by the need to create set in the teeth.
    Hard teeth are much more likely to break during the setting process.
    Although much less likely I'd much rather the teeth go blunt if they accidentally strike something hard than snap off.

  4. #18
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    Quote Originally Posted by BobL View Post
    A difference in RC hardness of around 10 is needed between the file and the metal being filed to easily file the metal and not rapidly ruin the file.

    The hardness is also limited by the need to create set in the teeth.
    Hard teeth are much more likely to break during the setting process.
    Although much less likely I'd much rather the teeth go blunt if they accidentally strike something hard than snap off.
    That's one of the reasons I want to do more here. Modern metallurgy has advanced tremendously since Disston's day so I am certain that handsaws can be better than they ever have been. Disston used Rc 52, which was best for the steel that was state of the art then.
    I also have a couple of modern pull type saws with induction hardened teeth. They are fine for soft pine but the teeth tend to break on anything harder. Obviously the lowest possible specification steel for low materials cost.

  5. #19
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    Quote Originally Posted by rob streeper View Post
    I also have a couple of modern pull type saws with induction hardened teeth. They are fine for soft pine but the teeth tend to break on anything harder. Obviously the lowest possible specification steel for low materials cost.
    I have a couple of those saw and have put one in particular through fair bit of often dirty aussie hardwood until it became very blunt, without breaking any teeth. What I have noticed with those blades is that they also seem to be made with minimal set so after a bit of wear they jam very easily.

  6. #20
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    Quote Originally Posted by BobL View Post
    I have a couple of those saw and have put one in particular through fair bit of often dirty aussie hardwood until it became very blunt, without breaking any teeth. What I have noticed with those blades is that they also seem to be made with minimal set so after a bit of wear they jam very easily.
    Ditto for an Irwin, induction-hardened, japanese-style tooth, push-saw. about 40 thou sawblade untapered.

    Rob - it would be interesting to know what reading you'd get from an Acme 120 or the equivalent Backsaw (77??)

    Cheers,
    Paul

    (I have one if Bob is able to measure it. Would it be uniform across the whole sawblade?)

  7. #21
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    Rob

    Good thread. It gets us going

    Regards
    Paul
    Bushmiller;

    "Power tends to corrupt. Absolute power corrupts, absolutely!"

  8. #22
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    Quote Originally Posted by pmcgee View Post
    Would it be uniform across the whole sawblade?
    That's a very interesting question Paul

    Looking at http://www.disstonianinstitute.com/factorytour.html from Henry Disston and Sons, Inc., Lumberman Handbook, Published 1907, the saw plate is hardened "edge first", followed by hammering ("smithing" and "tensioning").


    Regards
    John

  9. #23
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    My understanding of the constraints of a saw plate are twofold.

    Firstly they have to be sharpenable with a standard triangular file.

    Secondly you must be able to set the teeth without them snapping off or stress fracturing and breaking at a later date.

    This pretty much dictated the maximum hardness that was practical, being RC52

    They did experiment with no set saws such as the Disston 120 and that was harder although I don't know what it was. They also used a special shape file to sharpen and that is no longer available. Today with that 120 it has to be sharpened conventionally with a triangular file and, from what I have read, there is the distinct possibility that the teeth will break. Consequently I suspect they tend to be collector saws rather than user saws.

    Even with modern steels there is still the issue of sharpening with a conventional file. Until file steel catches up with "modern" steels the limitation Henry and his descendants experienced up to and just after WW2 still exists today.

    We do have machine sharpening available and quite possibly that can cope with harder steels, but I have no information on that. I also have to say that if we are chasing the supreme saw plate, we are rather defeating the object if we then have to machine sharpen which most seem to agree is inferior to hand sharpening by skilled persons.

    Please don't misunderstand my comments as I think this is an admirable thread and I find information like this fascinating. I also suspect that the major saw makers of the early twentieth century relied heavily on flowery marketing phrases, which in the main part could not be easily verified. Consequently there was probably quite a wide range of variation in the product. Your testing may well de-bunk some of their more outlandish claims.

    Much of the "excellence" in their high range saws was probably cosmetic (finish of the plate, etching, tote carving and tote material) and only a small part practical. By this I mean how much extra tempering, hammering and tapering went into a saw plate. Sure, tapering can be measured. Nowadays very easily with a digital vernier guage, but not so easily at the time of manufacture by the customer. Again, don't misunderstand me as I love those cosmetic touches and actively seek them out. It is a luxury the hardworking carpenter of the day could hardly justify. Today I still can't justify it, but it doesn't stop me .

    Regards
    Paul
    Bushmiller;

    "Power tends to corrupt. Absolute power corrupts, absolutely!"

  10. #24
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    Quick update:

    The salts have arrived. I melted some today - no drama. The melt was well behaved, brown (technical grade KNO3) and did not react badly to the few leaves that fell in the pot while I was watching it. It is clear however that I need an insulated pot and higher wattage heaters. I used a 750W hotplate with the salt in a welded rectangular stainless pan. The hotplate was only able to bring the melt temperature to about 200 C. The references say 210+ for 1095 steel. I'm thinking dual pots with a sand bath to retain heat and a couple of more powerful hot plates. More updates as I make progress.

    Cheers,
    Rob

    Salt_Bath_Quenching.pdf

  11. #25
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    Wow Rob that is quite an undertaking !! Bath salts sounded so relaxing...

    Regards
    John

  12. #26
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    Hey - you might wanna go down this path ... http://www.wkfinetools.com/tMaking/z...el-Markham.pdf

    Hardening in a Lead bath sounds like fun for all the family ... and ... don't forget the Cyanide of Potash.

    lead bath.JPG

    but actually on pg 178 it starts to talk about hardening thin plates ... and seems to favour compression between matching plates.

    Cheers,
    Paul

  13. #27
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    I have read through a lot of that book, far too hard for me to harden steel. I'll stick to buying old saws at markets and retoothing them if I need to.
    I am learning, slowley.

  14. #28
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    Quote Originally Posted by Pagie View Post
    I have read through a lot of that book, far too hard for me to harden steel. I'll stick to buying old saws at markets and retoothing them if I need to.
    Fred.JPG

    From life's school of war: what does not kill me makes me stronger

  15. #29
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    Quote Originally Posted by Bushmiller View Post
    .....
    Firstly they have to be sharpenable with a standard triangular file.

    Secondly you must be able to set the teeth without them snapping off or stress fracturing and breaking at a later date.

    This pretty much dictated the maximum hardness that was practical, being RC52
    ............
    Even with modern steels there is still the issue of sharpening with a conventional file. Until file steel catches up with "modern" steels the limitation Henry and his descendants experienced up to and just after WW2 still exists today.

    We do have machine sharpening available and quite possibly that can cope with harder steels, but I have no information on that.

    Regards
    Paul

    Good Morning Paul

    All good stuff. Even if we can machine sharpen supremely hard "modern steels" we are still left with the brittleness issue, are we not?

    Years ago I bought a set of stainless steel Gerber kitchen knives in a shield shaped wooden rack - looked really great, worked well, stayed shiny, held their edge really well - eventually they required sharpening and that was a real task due to the hardness of the steel. But I can wear that. A "bonus" and matching cleaver came with the set - I butchered a pig and finished up with three chips out of the blade of the cleaver and multiple fine cracks from the blade edge. Gerber's "life time" warrantee did not cover "abuse" such as chopping with a cleaver! Within a couple of years many similar fine cracks appeared in the cutting edges of the knives and two of the blades simply snapped. Gerbers standard answer was that it was not covered by warrantee as the knives had been abused.. That lovely looking stainless steel was simply too hard and too brittle for the task. Great to look at, but not fit for purpose.




    Fair Winds

    Graeme
    I will never again buy crap tools.
    I will never again buy crap tools.
    I will never again buy crap tools.

  16. #30
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    Quote Originally Posted by GraemeCook View Post
    Good Morning Paul

    All good stuff. Even if we can machine sharpen supremely hard "modern steels" we are still left with the brittleness issue, are we not?

    Years ago I bought a set of stainless steel Gerber kitchen knives in a shield shaped wooden rack - looked really great, worked well, stayed shiny, held their edge really well - eventually they required sharpening and that was a real task due to the hardness of the steel. But I can wear that. A "bonus" and matching cleaver came with the set - I butchered a pig and finished up with three chips out of the blade of the cleaver and multiple fine cracks from the blade edge. Gerber's "life time" warrantee did not cover "abuse" such as chopping with a cleaver! Within a couple of years many similar fine cracks appeared in the cutting edges of the knives and two of the blades simply snapped. Gerbers standard answer was that it was not covered by warrantee as the knives had been abused.. That lovely looking stainless steel was simply too hard and too brittle for the task. Great to look at, but not fit for purpose.




    Fair Winds

    Graeme
    I will never again buy crap tools.
    I will never again buy crap tools.
    I will never again buy crap tools.
    Graeme

    The short answer is that there was never much room to manoeuver regarding edge retention and brittleness.

    Your experience with kitchen knives is a good example of as the "quality" of the knife increases, it's usefulness lessens and it's specialised nature becomes evident. Japanese kitchen knives are a good example of this in that they are super sharp, but you have to be extraordinarily careful what you cut with them as they will chip even if they look at a piece of bone. Incidentally, you have to try a Japanese kitchen knife if you really want to experience sharp .

    I would suggest that Gerber's lifetime guarantee would have been challengeable, but hardly worth the effort.

    Take the Disston 120, which had a harder saw plate, was carefully taper ground and consequently was sold requiring no set: It was recommended to be used in seasoned hardwoods as it had the potential to jam in green or fluffy softwoods. It had become more specialised. Disston were not the only manufacturer to try the no set approach. Atkins' No.52 was the same deal.

    Regards
    Paul
    Bushmiller;

    "Power tends to corrupt. Absolute power corrupts, absolutely!"

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