If you've been following my 6BR thread you may be aware that I ran into some issues using smaller diameter indenters to measure BHN with my homemade tester, so I'm going back to the drawing board. First up, my original 10mm indenter had been turned on a lathe, and while the lathe did a pretty darned good job, there were some microscopic imperfections on the tip of the indenter. The imperfections don't show in this photo so you'll have to take my word for it. Anyway, I splurged on some 10mm ball bearings and epoxied a ball bearing into a 5/8” thingamajiggy that fits into my push-thru die holder. I used to measure the indentations with calipers and a magnifier, but then someone pointed out that Gimp (and some other free photo editing programs) have a “measure” tool. Take a photo of the indentation with some sort of scale in the picture, then you can zoom in on the photo and measure the indentation with accuracy limited only by the resolution of the photo. A USB microscope works well for taking the photo, but some cameras and even phone cameras are capable of taking decent closeups.Load the photo in Gimp. Measure the scale (this one is marked in tenths of an inch). In this example, the measurement across 0.300” on the scale was 569 pixels. In other words, the scale of the photo is 569 pixels per 0.300 inch, or 1897 pixels per inch. Next I measured the diameter of the indentation. I actually measured in several different places: 257 pixels, 257 pixels, 261 pixels. Well, the cat was chewing on my arm when I took the last measurement! Average of the three measurements = 258 pixels. To convert that to inches, divide 258 pixels by 1897 pixels per inch, = 0.13618 inch. The applied load was 150 kg. for 30 seconds -- more on how I apply the load later. Plug the numbers into the formula for BHN (a spreadsheet crunches the numbers for me) and we get 15.6 BHN. Should we believe that number? Well, the alloy was 50% lino and 50% clip-on wheelweight, and I was expecting 16 BHN. That's pretty close. In the next few days I'll try to post measurements for all my alloys including “known” standards like pure lead and linotype. Then I'll repeat the tests with different indenters and different loads and see how the results stack up. Most people buy store-bought BHN testers and that's fine, but like many casters I enjoy making my own stuff whenever possible. I'm not going to run out and buy a store-bought tester, but if anyone wants to loan me their store-bought tester, I'll be glad to include it in my comparisons.
BHN Measurement Revisited
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- Last Post 07 August 2016
Very interesting. This scratch approach is the same tactic geologists use to measure mineral hardness. The “scratchers” are ten known minerals ranging from talc to diamond if I am correctly remembering my geology class from 60 years ago.
I gotta have a set of those pencils.
There is no end to the stuff to learn. John EXACTLY John! I remember Earth Science Lab in high school learning how to preform the Mohs Hardness Test with mineral samples. It takes a good skilled hand to do that well, but is a good test.
Gary
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Very interesting. This scratch approach is the same tactic geologists use to measure mineral hardness. The “scratchers” are ten known minerals ranging from talc to diamond if I am correctly remembering my geology class from 60 years ago.
I gotta have a set of those pencils.
There is no end to the stuff to learn. John
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There is a trick to the pencil test, an artist friend pointed out to me. The shape and condition of the point of the pencil lead is IMPORTANT. A sanded flat point then scribbled on paper to smooth the flat and round the sharp off the edge works best. If you have a sharp edge or a sharp point that catches, the test will be erratic and inaccurate. You have to decide if the pencil will only write on the test sample or if it will scratch the sample.
The test works as well as you do it and I was happy with the method after I played for a while. I believe it is a useful test method. The pencil set I got cost me $10 at OfficeMax.
Gary
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I wanted to try the pencil method just to say that I tried it. :D
The name brand pencils that were recommended:
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Thanks for the good info, frnkeore. :)
I interpret E.H.H. as saying a large indenter is better because big indentations are easier to measure than little indentations ???
Dennis Marshall sometimes used the Meyers test. If I remember correctly, Dennis stated that you could convert Meyers to BHN simply by subtracting 1, but your link suggests that the relationship is non-linear.
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I'm sorry that I'm late (again) with getting the info to you, that I wanted you to see. In E.H.H. other info on testing, he states that you need a ball of at least 1/2” diameter, in this one, he says that 1” is best. My 5/8's ball was the closest I had on hand.
I don't know if you've heard of the Meyer Hardness test (I hadn't) but, it seems to have some relavance.
<url=http://www.digplanet.com/wiki/Meyer_hardness_test>http://www.digplanet.com/wiki/Meyer_hardness_test</url>
I hope this info many be helpful in your testing. I've enjoyed your results very, very much.
Frank
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I edited post #47 to use my equation for the “cylinder sandwich” instead of the “NRA equation.” It's late at night and my brain is not firing on all cylinders so you won't hurt my feelings if you check my math and point out any errors. :D :D :D
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goldilocks might pick a lucky 7 mm ball ...
wonder where that dang formula came from anyway ...
good stuff .... it makes me nervous when experiments come out just the way they were predicted ....
ken
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You've gone through a lot of work in doing all that, thank you.
I have some more info that I'll post a little later. I have to photograph it first.
Frank
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In an effort to better understand why a 10mm test seems to read higher BHN than a 4mm test, I did a side-by-side comparison using the “cylinder sandwich” method with both 4mm and 10mm balls. The cylinder sandwich method eliminates any error due to applied force because both samples receive exactly the same force and it cancels out of the BHN equation. The only remaining error is in how well you can measure the indentations, and that error is negligible using digital photo measurement. I made a gadget to hold two 4mm balls in the center of the 1/2” slitted pex. Initially I ran this test with the “NRA equation” that someone had posted. Later I went back and worked out the math from scratch and came up with a different equation, below. It's late at night and I'm tired so feel free to check my math and tell me if you find a mistake. The test results data: The test results graphed. As you can see, the 10mm ball read higher than the 4mm ball, more so on the harder bullets. I don't know why this is so, I only know that the results are repeatable, so it appears to be a fact of life. Which is more correct? Well, if you believe that 20:1 should be 10 BHN and linotype should be 21.5 BHN, then the 4mm results look reasonable and the 10mm results look too high. At this moment I have no explanation but I'll continue to investigate as time allows.
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On second thought, you do not have to include a scale. You only have to mic your bullet base and use that dimension as the scale, for both the On Target and mtngun's system.
Frank
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If you have the program, On Target (part of QL or seperate), you can do the same thing. You use your camera and import the picture to the program. You still must include a scale in the picture. Frank
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A USB microscope is a digital camera/microscope that runs off a USB port on your computer. They generally use webcam software to run the scope, though some are supplied with their own software.
I'm still experimenting with different free webcam softwares. Some only take 600 pixel photos while others go up to 1600 pixels. More pixels is better. Some do a better job of controlling the lighting than others. I've found that turning the scope's light way down and shining a flashlight on the specimen at an angle gives better definition of the indentation.
Both Gimp and Irfanview are free graphics programs that have a “measure” tool that allow you to measure the width of the indentation in pixels and compare it to the scale that you'll need to include in the photo.
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mntngn, "A USB microscope is very nice for photographing indentations,” What is a “USB microscope” , Where can I get one and approximately how much does one cost?
Lifetime NRA since 1956, NRA Benefactor, USN Member, CBA Member
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Just as a matter of (perhaps) interest to the person who posted about the possible submarine ballast: As I have read in my studies, virtually every D/E (Diesel/electric) boat launched, (at least the Balao Class) shipped approx. 65 tons of lead ballast. This varied according to any configuration change: if a deck gun was installed, from a 3” bore, up to the 5” 28 that could be installed fore or aft of the conning tower, Skipper's preference. The Installation configuration dictated quantity of lead required. I realize this has little to do with cast bullets, I just thought some folks might be interested.
Bill
In theory, there's no difference between theory and practice. In practice, there is. My fate is not entirely in Gods hands, if I have a weapon in mine.
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I have the Lee tester but have started using the pencil more. For someone with poor eyesight the Lee tester is difficult to read. I would love to find an old microscope to use one day. THe pencils run pretty good, just make sure you keep the edge sharp. I was skeptical at first but now am comfortable with a #2 pencil at the scrap yard.
Jim
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I'm about convinced to buy the Lee tester. I have scrounged a lot of lead over the years and most of it is a mystery alloy. I think I may even have what I've been told is submarine weights. Movable ballast I guess. The old WWII sub base is not that far. May have traveled over here. Nobody alive knows what's in it but all I really need to know is approximately how hard it is. Something a little more specific than the thumbnail test. I confess to being the least scientific CBA member in my neighborhood!
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And disrespectful, as well joe, considering he was one of the founders of the CBA!
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Very interesting. Anybody still trying the artist's pencils method any more?
I put Ken Mollohan's article on pencil- lead- hardness- testing up here, somebody took it down. Not scientific enough, perhaps.
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