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  1. #76
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    I just found that I had made an Excel error in calculating the standard deviations. I've corrected it in this table.

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  3. #77
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    Quote Originally Posted by rob streeper View Post
    I just found that I had made an Excel error in calculating the standard deviations. I've corrected it in this table.

    As to the high values on the Disston saws another thought just occurred to me. Given my posting on my D-8 replica page where I found that hammered areas of 1095 are remarkably hard and given the fact that I measured these hardnesses under the handles I wonder if I'm measuring in the hammer hardened zone of the blade? More testing tomorrow...
    Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.

  4. #78
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    Quote Originally Posted by rob streeper View Post
    Hi Ray,
    Most of my measurements have been on the 15N and 30N scales with 45N measurements only where the thickness of the test article warrants.
    That's the wrong scale... Rockwell N scale not Rockwell C, you need to do a conversion. ( and a thickness correction. )

    From the ames charts 50 on the 45-N scale is Rc 46, and 50 on the 30-N scale is Rc 30... lowest number on the 15-N scale in the conversion charts is 69.5, which is 20 Rc

    Also, a superficial tester is not specifically designed for thin material, it's designed for surface hardness measurement.. You need to apply corrections for material thickness.

    A general rule of thumb is that you can't measure materials where the depth of the indentation is more than 1/3 of the material thickness...

    Ray

    PS Here is a conversion chart to convert from Superficial N scales to Rockwell C
    http://www.buehler-asia.com/brochure...s_Table_01.pdf

  5. #79
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    Quote Originally Posted by planemaker View Post
    Hi Ray. On Sawmill Creek George Wilson and David Weaver raised similar concerns regarding the validity of the test results.

    Having little knowledge on the subject of Metallurgy I am not in a position to form an opinion.

    Stewie;

    http://www.sawmillcreek.org/showthre...w-plates/page2
    Hi Stewie,

    Thanks for that, I just quickly scanned the thread, I agree with what they are saying, something is seriously wrong with the measurements.

    Ray

  6. #80
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    Quote Originally Posted by RayG View Post
    That's the wrong scale... Rockwell N scale not Rockwell C, you need to do a conversion. ( and a thickness correction. )

    From the ames charts 50 on the 45-N scale is Rc 46

    Also, a superficial tester is not specifically designed for thin material, it's designed for surface hardness measurement.. You need to apply corrections for material thickness.

    Ray
    Hi Ray,

    I used the conversion charts to produce the Rc values reported. NIST recommends the N scale for thin hard materials and they recommend the highest loading permissible for a given test material thickness. Look here: http://qs-hardnesstester.com/hardnes...thickness.html

    Referring to the linked chart and given that we're talking about materials that should have Rc hardnesses of 45 or greater you can see that the minimum thickness recommended for a C scale measurement is 0.034" for Rc45. If the material is harder, say Rc 52 then the minimum thickness decreases to 0.032" and so on.
    Look to the right side of the chart now at the N scales. You will see that for a 0.015" thick test article that the minimum Rc value is somewhere between 68 and 76. Thus N15 testing of 0.015" materials is not really that good. However, on the N30 and N45 scales you will see that the minimum thicknesses recommended are 0.022" and 0.024" respectively. All of the saws I tested have thicknesses equal to or greater than than 0.022".
    To accurately measure 0.015" material I need to go to the 15T or 30T scales, something I need to do in the future obviously.

    Please understand that I am doing these studies because I am interested. I have searched the web and have not found any systematic study of the hardness values of woodworking saw blades. I wonder why?

    Cheers,
    Rob
    Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.

  7. #81
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    Hi Rob,

    Thanks for that...

    I haven't ever been able to do proper hardness testing on thin materials, On the Avery the Rockwell C standard load of 150Kg leaves an indentation too large. That's the area where you need the lighter loads of the superficial scales. But you still need to apply corrections for thickness.

    That is a problem, since you usually have to add something for thickness, and your numbers are already way too high.... so I'm still mystified as to what could be wrong.

    Ray

    PS Can you post your raw data for the Sawmaker No4 and what scale you used.

  8. #82
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    Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.

  9. #83
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    Ray,

    I used the 30N scale for the majority of the measurements. Where the saws were thick enough I also used the 45N scale. The correspondence of the measurements was very good. I see now that I mistakenly said that the thinnest saw I tested was 0.022", in fact it was 0.020" but nonetheless for the hardness measured it was still within the acceptable thickness range for the N30 scale.

    Aside from all of the bickering going on about whether I used the correct scale I haven't heard anybody opine on the consistency of my results. As I posted much earlier on this thread, if I used the C scale testing on material that was too thin and tested several samples the relative hardnesses would still be comparable even though the absolute values would be wrong.

    Why pray tell is this such a contentious issue and why has nobody ever looked into this and posted some results?

    Cheers,
    Rob
    Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.

  10. #84
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    Hi Rob,

    That's not the raw data.. that's the data after conversion and correction. What I was interested to see is the actual numbers from the ames tester.

    Ray

  11. #85
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    Quote Originally Posted by RayG View Post
    Hi Rob,

    That's not the raw data.. that's the data after conversion and correction. What I was interested to see is the actual numbers from the ames tester.

    Ray
    I was doing the testing on the fly, meaning that I took the reading, looked at the chart and typed the result into the spreadsheet.
    Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.

  12. #86
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    Quote Originally Posted by rob streeper View Post
    I was doing the testing on the fly, meaning that I took the reading, looked at the chart and typed the result into the spreadsheet.
    Ok, next time you are doing a test, record the actual readings direct from the Ames out of interest.. maybe that will help unravel the mystery.

    Quote Originally Posted by rob streeper
    Why pray tell is this such a contentious issue and why has nobody ever looked into this and posted some results?
    I don't know that it's all that contentious, certainly it's very interesting and not something that's been done all that much before.
    The thing I do know for sure and that is that at least some of the data is wrong.. Rc 60 cannot be correct.

    Ray

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    Quote Originally Posted by RayG View Post
    The thing I do know for sure and that is that at least some of the data is wrong.. Rc 60 cannot be correct.

    Ray
    You mean for maker number 4? If so I will tell you that it is a different saw design from the other saws. Any more and I could get even more trouble that I currently have.

    BTW: The instrument I have was manufactured in 1969, well before the advent of USB connections.
    Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.

  14. #88
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    It would be interesting to do a map for an old Disston.
    Despite the relatively recent development of a repeatable hardness test with Rockwell, I'm sure that the old saw makers could tell if a saw was hard or soft with out it.
    Anecdotally, they could tell from the sound it made when struck.
    If tensioning can locally increase the hardness of a thin plate then the hardness of the raw plate many be of less importance. This is certainly the case with modern hard point saws.

    I suspect that saw plate for all saw makers was extremely varied in quality in flatness and hardness but this was evened out by the skilled saw maker in construction through grinding, toothing, setting and tensioning. Each process contributing to the smoothness and hardness of the saw.

  15. #89
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    Quote Originally Posted by RayG View Post
    Hi Stewie,

    Thanks for that, I just quickly scanned the thread, I agree with what they are saying, something is seriously wrong with the measurements.

    Ray
    Now I know why Sawmill Creek has the reputation that it does. The posters there have formed a club and outsiders are not welcome. I checked the thread from yesterday and Prashun Patel, I assume one of the moderators, is going back and revising all of the posts and has deleted many. Auditing reality to make it pretty has a bad smell to me.
    Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.

  16. #90
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    Quote Originally Posted by hiroller View Post
    It would be interesting to do a map for an old Disston.
    Despite the relatively recent development of a repeatable hardness test with Rockwell, I'm sure that the old saw makers could tell if a saw was hard or soft with out it.
    Anecdotally, they could tell from the sound it made when struck.
    If tensioning can locally increase the hardness of a thin plate then the hardness of the raw plate many be of less importance. This is certainly the case with modern hard point saws.

    I suspect that saw plate for all saw makers was extremely varied in quality in flatness and hardness but this was evened out by the skilled saw maker in construction through grinding, toothing, setting and tensioning. Each process contributing to the smoothness and hardness of the saw.
    If you've got an old Disston having a nice shiny blade I'd be happy to test it and report the results. Unfortunately the testing will leave little prick marks all over the plate which would have a detrimental effect on it's value. As I wrote above in correspondence with BobL I'm going to test a piece of 0.035" steel straight from the roll. I'll also take a piece and hammer one end, grind it flat and test the hammered and un-hammered portions. If the results I've seen for the D-8 saw plate I'm working on are reproduced the hammered end should be harder.

    The problem with the sound tests, and I do those too, is that there's no intelligible way for me to report that kind of information on this website. I agree that the sound is different, generally higher in pitch but then again I'm sure that the plate is ringing in frequency bands well outside the range of human perception.

    I think it's time that we banish these notions, meaning the various bits of received wisdom like Disston's 52, that we all think we know but that nobody has tested systematically. Everybody seems to have an opinion but nobody can offer any data. Why is that?
    Innovations are those useful things that, by dint of chance, manage to survive the stupidity and destructive tendencies inherent in human nature.

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