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Thread: Hardness testing of saw plates

  1. #1

    Hardness testing of saw plates

    I just posted a comment on an old link regarding some hardness testing I have done and one of the members suggested I create a new thread with the information.

    I've been building saws for about two years now and have become interested in the technical aspects of saw design. In my reading I have found that Disston at some point or other decided that the optimal hardness for saw plates was Rockwell C 52. The saw building community uses blued spring steel in sheet or rolled sheet form, often 1095 in building custom saws for the boutique market. My nature is to question things, especially benchmarks that were established a century ago like Disstons Rc52, and thus I set out to learn about the hardness of saw plates.
    I recently acquired an Ames 2-S hardness tester. This instrument measures superficial hardness on the Rockwell N and T scales. This device works by measuring the depth made on the test article when a measured load is applied to a point called an indenter. On the N scale it uses a specially shaped diamond point and on the T scale it uses a 1/16" carbide ball. For hard materials you use the diamond and for softer you use the ball. The N and T scales specify three different loadings, 15, 30 and 45kg for different thicknesses of test materials. This links to a table giving the appropriate loading and indenter for various test article thicknesses. http://www.continentalht.com/userfil...sion-chart.pdf See the Hardness vs Minimum Thickness Chart at the top left of the first page.

    Here's the instrument.

    Ames 2-S hardness tester 2.jpg


    And here's the data.



    The conclusions I draw are:

    1) 1095 steel is a consistent product. Despite the fact that the test materials were purchased from different sources over a period of several years the hardness values for the products were all very similar with a remarkably low standard deviation of 0.34 Rc points. Plus these tight results show you that both my technique and my hardness tester are working well.

    2) Of the custom makers, only one is using 1095 steel. The other two makers represented in my collection are using softer material. Maker 3 is using very soft metal, 40% softer than 1095, - likely because it's cheaper and/or easier to work with. Maker 2 is using something that is about 7% softer. The highly significant t values (t < 0.05) for these measurements indicate a high degree of confidence that the measurements are not due to chance.
    Maker 2's saws work just fine for me, but I'm not using them for production work. Makers 2 and 3 are names that everybody in this area knows well so I won't reveal them.

    3) Disston's products varied in hardness over the years. The Disston saws in my collection were manufactured in the period spanning post WW1 to post WW2. The variability is not too surprising because the concepts of industrial quality control were in their infancy in the early 20th century. Disston also used steel that is harder by just under 4%, or 2 Rc points, than is 1095 but the difference is on the edge of statistical significance (t = 0.04).

    Sharpening old Disston saws is going to be harder on your files than is sharpening modern saws. If you're really worried about the longevity of your files get some saws from Maker 3 and your files will last a long time but you may not get much wood cut.

    Further, modern custom saws made with raw 1095 steel are not as hard as are older Disston saws. If the plate hardness is important and if Disston optimized his products we've actually taken a step backward in our unquestioning use of 1095.

    I'm gonna go lick my wounds now.

  2. #2
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    would there be any way to find out who is "custom maker 3"? I am about to buy several backsaws and would rather have harder than softer steel.

  3. #3
    Quote Originally Posted by David Dalzell View Post
    would there be any way to find out who is "custom maker 3"? I am about to buy several backsaws and would rather have harder than softer steel.
    Hi David,

    Sorry, I can't tell. I'm sure you understand that I would incur significant liability if I revealed that information and it's likely that the Sawmill Creek administrators wouldn't be too happy either. I debated with myself the wisdom of making this post but ultimately decided that I would do a disservice to the community if I remained silent so I settled on the compromise of anonymizing the names of the makers.

    I'd suggest that you ask the saw makers you are considering about the steel that they use and whether they test each lot of their stock for fitness for use.

    Given the significant investment that some of us make in these custom made saws I don't think it would be a bad idea to invest in a hardness tester for personal use. I have a lot of money in my saw collection and it really disappoints me to learn that I have been taken advantage of.

    BTW, I have some chisels I'm suspicious of too...

    Caveat emptor

    Cheers,
    Rob
    Last edited by Rob Streeper; 01-11-2015 at 7:42 PM.

  4. #4
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    I figured that would be the case. Everyone seems sue happy these days. I did enjoy your article.

    David

  5. #5
    Thanks David, sorry I can't be more forthcoming. I'll be continuing my saw blade hardness work.

    Cheers,
    Rob

  6. #6
    I'm not in the USA so not sure on the legal ways over there. But surely reporting facts i.e this saw from this maker tested at…. Can't be liable???

    How often do people writing reviews that are condemning or critical get sued? If they do and that leads to all independent reviews only commenting on the positive then the reviews are worthless, even if it is just a subconscious bias on the basis of how they word it to not offend.

    What happened to free speech?

    I say to all manufacturers stop using scare tactics and make a quality product where you have nothing to hide and can take pride in your product. That would make for a much better world.

  7. #7
    Rob, Have you had a chance to test the new breed of production saws i.e. LN & LV or just the custom makers?

  8. #8
    Hi David,

    People are getting sued by companies here for writing negative comments on the Internet. See: http://www.forbes.com/sites/investop...eview-on-yelp/

    Speech is still free in America as long as nobody objects to what you have to say - that's why I have to be careful.

    As to Maker 3 and the results I got, who knows. Maybe it's a one-off problem. Maybe one lot of steel was unevenly hardened.

  9. #9
    I put anybody who charges more than $75 or so for a hand saw into the 'custom makers' category.

  10. #10
    I realized over dinner that I have saws from an additional custom maker so I've updated the data table to include tests on their saw too. I also included measurements of the blade of an Atkins No. 26 pattern makers saw having a Silver Steel blade.Their saw is at the extreme upper end of hardness, Rc 61.4. Special type of saw. I'll enter some more data tomorrow as I have a few more Disstons to test.
    Last edited by Rob Streeper; 01-11-2015 at 11:51 PM.

  11. #11
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    I don't know what happened to my previous post. There are 3 different N and T scales. I only ever used the Rockwell C scale,in which the usual 1095 spring steel that everyone uses was a consistent 52 Rc. Much harder than that and it is impossible to file the saws,or to keep the blades from breaking in use because of being too brittle.

    I don't understand your figures,therefore.



    These different scales are for specific steels and materials,too. You must use a scale that is intended for the type of steel you are testing. That,to be brief,is what my post was about. But,I'm too tired now to investigate further.

    I have not heard of anything but the C scale being commonly used to test spring steel. And,I have never seen an old saw that was harder than modern 1095 spring steel. That was just my own experience,of course,and I am not a collector of vintage saws,but have filed many.

    I am wondering how you have arrived at a hardness in the C scale of an Atkins saw at a bit over 61 RC scale. That would be totally impossible to file. What "special saw" would that have been?
    Last edited by george wilson; 01-12-2015 at 10:58 AM.

  12. #12
    Hi George,
    I think your response is on the original thread. I started a new one at the suggestion of another member.
    For these measurements I referred to this: http://qs-hardnesstester.com/hardnes...thickness.html to select the appropriate scale and loading.
    For most of these measurements I used the 30N scale. For the 0.015" 1095 I used the 15N scale even though it is somewhat below the minimum thickness recommended.
    The consistency of my measurements and the low standard deviation for the 1095 measurements indicate first that 1095 is very consistent material, second that I'm using the tester correctly and finally that the tester is operating correctly. The measurements on the test blocks included in the tester kit were spot-on despite the fact that the instrument was made in 1969. The low number of test marks on the blocks suggest that it spent most of the intervening years sitting on a shelf somewhere. Too bad as it's a beautiful instrument.

    Cheers,
    Rob
    Last edited by Rob Streeper; 01-11-2015 at 11:43 PM.

  13. #13
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    What country are you in that you cannot publish correct data on saw steels? Fine Woodworking does tests upon different tools such as chisels BY BRAND NAME,and has not been sued.

    I haven't investigated the odd scales you are using,but the words "superficial hardness",when the saw steel is not superficially hardened bother me,as does going below the minimum allowable thickness. Those things just MIGHT lead to inaccurate data.

    At work I had the cadillac of hardness testers,the Versitron,to get my results from. Had the test blocks and a new diamond also.
    Last edited by george wilson; 01-11-2015 at 11:50 PM.

  14. #14
    Here is a link to the company page for my tester. The Rockwell N and T scales are also known as 'superficial' hardness scales and the testers are superficial hardness testers. They are used for thin hard materials such as thin hard steels and case hardened surfaces.
    People get sued all of the time for writing critical reviews, even in Virginia. See: http://www.forbes.com/sites/investop...eview-on-yelp/. Poor lady is being sued for $750,000.
    Atkins used it's so-called Silver Steel in it's saws. See: http://www.tias.com/8600/PictPage/1922983474.html. I have no idea what 'Silver Steel' is but it is sure hard stuff.

  15. #15
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    This is excellent.

    Thank you for taking time to compile this.
    It's a terrific piece of work.

    This sort of essential data helps explain
    lots of things I notice in my hodge-podge
    collection of rehabilitated saws.

    I congratulate you on this article.

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