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Thread: Hardening of sawplates
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13th January 2015, 01:17 PM #76
I just found that I had made an Excel error in calculating the standard deviations. I've corrected it in this table.
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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13th January 2015, 01:41 PM #77
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.
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13th January 2015, 01:51 PM #78
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
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13th January 2015, 02:00 PM #79
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13th January 2015, 02:13 PM #80
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,
RobInnovations 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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13th January 2015, 02:28 PM #81
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.
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13th January 2015, 02:33 PM #82Innovations 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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13th January 2015, 02:38 PM #83
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,
RobInnovations 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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13th January 2015, 02:40 PM #84
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
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13th January 2015, 02:42 PM #85Innovations 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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13th January 2015, 02:52 PM #86
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.
Originally Posted by rob streeper
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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13th January 2015, 02:58 PM #87Innovations 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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13th January 2015, 08:37 PM #88GOLD MEMBER
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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.
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13th January 2015, 11:17 PM #89
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.
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13th January 2015, 11:39 PM #90
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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