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Thread: Testing hardness with pencils

  1. #1
    Boolit Man chasw's Avatar
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    Testing hardness with pencils

    I've been reading all the various posts about methods and devices for testing alloy hardness. One post by Molly recommended using pencils of varying hardness to compare against the surface hardness of bullets and ingots. This is widely used in labs to test hardness of metal coatings by scratching the surface in a particular way to see if the pencil digs into the surface or glides over it.

    After some searching, I found that Office Depot, a large chain of stationary stores here in the US, carries just what I needed - the Staedtler Mars Lumograph set of pencils for artists. Cost is $10 for the set of 12 wooden pencils in a flat metal case, already sharpened, ranging from 6B to 4H.

    Molly said 6B pencils are same hardness as pure lead and H equal to linotype. Can anyone provide an approximate BHN number for the other pencils in between? These are 6B, 5B, 4B, 3B, 2B, B, HB, F, and H. The set continues on up to 2H, 3H and 4H, but if H is lino, I won't be using alloys any harder than that. BTW, I tried out the pencils on the base of a fresh bullet cast from what I believe to be Lyman no 2. F scratched the surface, but HB just left a trail of graphite on the shiny surface, as predicted.

    I really like this method. Its quick, cheap and repeatable. No spring loaded devices, no ball bearings, no measuring indents with a digital caliper. Just apply the pencil and see immediately if it scratches or writes. You assistance in converting the pencil numbers to BHN is appreciated. thx - CW
    Three millions of people, armed in the holy cause of liberty, and in such a country as that which we possess, are invincible by any force which our enemy can send against us. - Patrick Henry, March 1775

  2. #2
    Boolit Master on Heavens Range
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    Using the scraping idea is preferred in my opinion, as opposed to indenting, for the measurement of the leading potential. However, for the rotation grabbing ability, the indention measurement would be more important. ... felix
    felix

  3. #3
    Moderator Emeritus/Boolit Master in Heavens Range
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    Quote Originally Posted by chasw View Post

    Molly said 6B pencils are same hardness as pure lead and H equal to linotype. Can anyone provide an approximate BHN number for the other pencils in between? These are 6B, 5B, 4B, 3B, 2B, B, HB, F, and H. The set continues on up to 2H, 3H and 4H, but if H is lino, I won't be using alloys any harder than that. BTW, I tried out the pencils on the base of a fresh bullet cast from what I believe to be Lyman no 2. F scratched the surface, but HB just left a trail of graphite on the shiny surface, as predicted.

    I really like this method. Its quick, cheap and repeatable. No spring loaded devices, no ball bearings, no measuring indents with a digital caliper. Just apply the pencil and see immediately if it scratches or writes. You assistance in converting the pencil numbers to BHN is appreciated. thx - CW
    Chas,

    I can't give you an exact comparison beween pencil hardness and Brinnel hardness: Just never got around to it, as I didn't need to know any more than "Is it as hard as the last batch?" or "is it harder / softer than the last batch?"

    I suspect you can come pretty close though, as follows: Each pencil hardness seems to average roughly one and 3/4 Brinnel units harder than the one below it. I don't know that this is an exact amount, but it seems to hold over several steps of pencil hardness. Technique is important. You can get some reallly bad values if you don't take care that the pencil lead is 'full wadcutter' in shape, with a sharp edge. If you use a pencil that has a cone shaped point, heaven only knows what you'll come up with. Hope this helps.
    Regards,

    Molly

    "The remedy for evil men is not the abrogation of the rights of law abiding citizens. The remedy for evil men is the gallows." Thomas Jefferson

  4. #4
    Boolit Master
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    While the "scratch test" may seem to have appeal, keep in mind that it is a relative test. Much like the ole' trick of usin' 'yer thumbnail. Scratch that (pun definitely intended), it's exactly like using your thumbnail.

    A relative test has value in the sense that it allows one to quickly determine if a material is "harder" or "softer" than another. Unfortunately, the deficiency of any such test is that it fails to provide accurate numeric data, and as such, fails to allow reliable exchange of data between individuals. In other words, a relative test provides value only to the individual employing the test.

    In addition, there is no method known to "convert" results from such a relative test into BHN.
    Quite simply, one is a relative test employed to gain generic information, while the other (Brinell test) is a standardized test designed to provide a numeric result.


    An excerpt from an engineering forum I frequent:

    HARDNESS TESTING
    What is Hardness?
    Hardness is the property of a material that enables it to resist plastic deformation, usually by penetration. However, the term hardness may also refer to resistance to bending, scratching, abrasion or cutting.

    Measurement of Hardness:
    Hardness is not an intrinsic material property dictated by precise definitions in terms of fundamental units of mass, length and time. A hardness property value is the result of a defined measurement procedure.

    Hardness of materials has probably long been assessed by resistance to scratching or cutting. An example would be material B scratches material C, but not material A. Alternatively, material A scratches material B slightly and scratches material C heavily. Relative hardness of minerals can be assessed by reference to the Mohs Scale that ranks the ability of materials to resist scratching by another material. Similar methods of relative hardness assessment are still commonly used today. An example is the file test where a file tempered to a desired hardness is rubbed on the test material surface. If the file slides without biting or marking the surface, the test material would be considered harder than the file. If the file bites or marks the surface, the test material would be considered softer than the file.

    The above relative hardness tests are limited in practical use and do not provide accurate numeric data or scales particularly for modern day metals and materials. The usual method to achieve a hardness value is to measure the depth or area of an indentation left by an indenter of a specific shape, with a specific force applied for a specific time. There are three principal standard test methods for expressing the relationship between hardness and the size of the impression, these being Brinell, Vickers, and Rockwell. For practical and calibration reasons, each of these methods is divided into a range of scales, defined by a combination of applied load and indenter geometry.

    Hardness Conversion or Equivalents:
    Hardness conversion between different methods and scales cannot be made mathematically exact for a wide range of materials. Different loads, different shape of indenters, homogeneity of specimen, cold working properties and elastic properties all complicate the problem. All tables and charts should be considered as giving approximate equivalents, particularly when converting to a method or scale which is not physically possible for the particular test material and thus cannot be verified. An example would be converting HV/10 or HR-15N value on a thin coating to the HRC equivalent.
    In other words, please do not attempt to tell others your lead is "XX BHN" if you have not performed a Brinell test.

  5. #5
    Boolit Man chasw's Avatar
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    Thanks, Molly and Rob. This is useful information. As I begin to gather data from using my new pencil set on samples from my store of boolit alloys, I am beginning to map out a scale of sorts - call it the Staedtler Scale, after the makers of these fine artist's pencils. So long as one sticks to that widely available brand of pencils and uses the correct technique, results will be similar. Molly observed spacing of about 1-3/4 BHN between some of the grades, perhaps at the softer end of the scale. Here's what I've gathered so far:

    6B = Pure lead, about 5 BHN
    5B
    4B
    3B = 1in20 tin/lead alloy, age softened, about 10 BHN
    2B
    B
    HB = Lyman no 2 alloy, about 15 BHN
    H = Linotype, supposedly about 22 BHN, but that seems high
    2H
    3H
    4H

    I offer this cheap but effective method of testing relative hardness, not particularly to convert pencil numbers to Brinell numbers, but rather as an alternate scale for boolit casters, with reference points to known alloys. If I pick up some scrap lead, or buy alloy from a smelter, I can quickly find out where it lies, relative to those other alloys. For example, my small stock of LaserCast brand commercial lead projectiles tested HB. I never had any luck with them, I've been saving them for the furnace, now I know approximately where they fit in as feedstock.

    The bullets I cast from Lyman no 2 do very well in my rifles, with no leading at all. But methinks that alloy is too hard to maintain a tight seal in my revolver loads. So I'll try some of the 1in20 alloy, maybe with some Lino mixed in to boost it up into the 2B range. - CW
    Three millions of people, armed in the holy cause of liberty, and in such a country as that which we possess, are invincible by any force which our enemy can send against us. - Patrick Henry, March 1775

  6. #6
    Boolit Master
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    Got pencil set at A.C Moore

    went to local A.C Moore today Pencil set (see pic) was listed at $19.99 not $9.99 as was Office Depot.I got the manager and showed him the print out from Office Depot. He had no explaination. I told him I would buy the set at the Office Depot price or shop elsewhere. He say "Ok" Point is "My Mama said" You better shop around"Oh by the way I tested some 20-1 alloy i bought from a vender. It was 20-1 although I cant get it to mushroom when i use drilled out hollow points
    Last edited by Shooter6br; 05-23-2010 at 09:39 AM.

  7. #7
    Boolit Master
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    tried on my certified Lyman #2 and 20-1 Both as predicted

  8. #8
    Moderator Emeritus/Boolit Master in Heavens Range
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    Quote Originally Posted by rob45 View Post
    While the "scratch test" may seem to have appeal, keep in mind that it is a relative test. Much like the ole' trick of usin' 'yer thumbnail. Scratch that (pun definitely intended), it's exactly like using your thumbnail.

    A relative test has value in the sense that it allows one to quickly determine if a material is "harder" or "softer" than another. Unfortunately, the deficiency of any such test is that it fails to provide accurate numeric data, and as such, fails to allow reliable exchange of data between individuals. In other words, a relative test provides value only to the individual employing the test.

    In addition, there is no method known to "convert" results from such a relative test into BHN.
    Quite simply, one is a relative test employed to gain generic information, while the other (Brinell test) is a standardized test designed to provide a numeric result.

    In other words, please do not attempt to tell others your lead is "XX BHN" if you have not performed a Brinell test.
    May I comment? I really don't want to start a quarrel, but I feel you may be focusing too much on theoretical aspects and overlooking the "real world". You are correct in stating that the pencil hardness test will only provide relative hardness, not a numerical value. However, you are outright mistaken in stating that it "fails to allow reliable exchange of data between individuals." The pencil hardness test is not only a standardized test that is widely recognized and used commercially, it was tested and approved for reproducibility and consistency under the auspices of the American Standard Test Methods panel, whose 'round robin testing' found that when properly performed, the result obtained by one individual should not vary more than one pencil value from the results obtained by another individual in a different location and using a diferent set of pencils. Your local library can furnish you with full details.

    While you are also correct in principle in recommending that results not be reported as Brinell values unless an actual Brinell test has been conducted, there are some practical difficulties with that policy; Formal hardness testing equipment and procedures are unfortunately beyond the financial and or technical skills and resources of many shooters. The pencil hardness test provides a simple and inexpensive alternative. And while it does not provide Brinell numbers, it is not unreasonable for shooters to wonder if their "HB" alloy hardness is anywhere near the Brinell hardness of an alloy reported in literature.

    Even the best lead alloy hardness testing (indent measurement errors, quenching, age hardening / age softening, work softening and others) can result in considerable doubt of the reliability of even your vaunted numerical Brinell values. That ingot that tested 16 Brinell last week may test 14 or 18 Brinell today.

    Given the admitted lack of extreme precision of both techniques (especially over time), a simple table of aproximate equivalencies between Brinell and pencil test results is not without some practical value amongst the laity, no matter what theoretical objections there may be. I personally have no problem with statements like "I get a consistent () pencil hardness, which is roughly equal to () Brinell."

    In the final analysis, despite some theoretical concerns, either technique is a great deal better than scratching an ingot with your thumbnail or smashing two bullets together in a vise. Pencil hardness values are sufficiently precise that one can reproduce initial batch hardness and follow quenching / aging effects in your latest batch of alloy. And they are obtained with little difficulty or cost, and require little training. As a practical matter, Brinell hardness values don't seem to offer a great deal more.

    Molly
    Last edited by Molly; 02-17-2010 at 06:47 PM.
    Regards,

    Molly

    "The remedy for evil men is not the abrogation of the rights of law abiding citizens. The remedy for evil men is the gallows." Thomas Jefferson

  9. #9
    Boolit Man
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    The older Ames hardness testers can be found cheap and are easy to use.

  10. #10
    Moderator Emeritus/Boolit Master in Heavens Range
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    Quote Originally Posted by MJR007 View Post
    The older Ames hardness testers can be found cheap and are easy to use.
    ??? Ames??? Not familiar with them. How do they work?
    Molly
    Regards,

    Molly

    "The remedy for evil men is not the abrogation of the rights of law abiding citizens. The remedy for evil men is the gallows." Thomas Jefferson

  11. #11
    Boolit Man
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    Just have to convert from Rockwell: MY unit was made in 1980 and the same unit is still made today. They can be found used cheap.

    Ames Hardness Tester for Rockwell Testing
    The Ames Hardness Tester for Rockwell testing has been giving repeatable accurate measurements in large and small plants around the world for over 50 years. The light weight and portability of the Ames hardness tester saves time and money by providing Rockwell test results quickly, anywhere.

    Ames Portable Hardness Testers are built following ASTM E-110 Guidelines for making hardness testing measurements directly in the Rockwell scale, with no chart, conversion or calculation required. Penetrations are of correct width and depth.

    Unlike many units described as a portable or hand held hardness tester, the Ames Hardness Tester can take fully-accurate readings on the inside surfaces of objects simply by switching the positions of the anvil and penetrator.

    Every genuine Ames Hardness Tester is individually calibrated to the Rockwell scales before leaving our plant. The signed certificate with each unit reflects a painstaking process involving from 70 to 100 separate readings.

    Ames: over fifty years of excellence
    Ames Precision joined forces with Electro Arc Manufacturing Company in 1975. Ames portable hardness testers are still built one at a time with the same attention to detail and high quality standards our customers have come to respect. Thousands of Ames testers are in use worldwide.

  12. #12
    Boolit Master HORNET's Avatar
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    Let's see....Set of pencils new cost ~$10 at Office Depot
    Ames Hardness Tester new cost ~ $1650
    That used price for the Ames would have to go down an awful lot just to get below the price of a Saeco tester, a Cabine Tree tester, a Lee tester, and a set of pencils combined.....
    I'm sure the Ames is a good piece of equipment but some of us are froooogal......
    Rick
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  13. #13
    Boolit Man
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    The Ames units are very good, even the old ones like mine. I guess I like old tools. The design has not changed in over 30 years. It works very well and used ones can be found. It may be a little over kill for boolits. I guess there are many different ways to get the boolit on target.

  14. #14
    Boolit Master



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    Molly;
    An excellent post in every way. I am a bit jealous of your way with words.

    Thanks for sharing with us.

    As a matter of interest, I have long had an LBT hardness tester and have been very happy with it. However, I have no illusions that it is PRECISELY accurate. However, it IS comparatively accurate and serves the purpose quite well. Sometimes we get carried away with the promise of PRECISION that is way beyond what benefit we can realize.

    I suspect that most of us could get by quite nicely with pencil hardness testing. If I had known that before I bought my LBT, you can bet your house that is what I would be using now.

    Dale53

  15. #15
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    Thank you gentlemen. This thread is an excellent example of the knowledge that abounds on this forum.

    Chasw, your efforts to come up with somewhat a correlation between the pencil leads and the brinnell scale is a very good idea that will be a lot of help to those who haven't yet purchased a tester or who simply want an idea of how hard their lead is. Good on you.

    Edd
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    Forum member on sticky people: "Consider the clown(s) just one of God's little nettles in the woods, don't let it detract from the beauty. Sooner or latter you are going to run into the nettles regardless of how careful you are. The itch passes faster if you don't scratch it."

  16. #16
    Boolit Buddy
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    Picked up a set of 10 artist pencils for $8.50 in Walmart. It contained an 8B, 6B , 4B, 3B, 2B, B, HB, F, 1H, 2H, 3H and 4H.
    Tested a few things I had laying around just for grins.
    Egg sinkers I cast from lead sheet that I think is nearly pure lead- 8B
    Bullet I cast from Clip on WW- 3B
    Commercial bullet from Tennessee Valley Bullets (supposed to be around 12 bhn)- B
    Ingot of Clip on WW with 2% tin added- B
    Ingot of Commercial Hardball Alloy- F
    Commercial Rifle Bullet from Hunter's Supply- F
    Commercial Bullet from Meister- F
    Bullet I cast from clip on WW's and water dropped- 2H

    I'm not sure I can nail down an exact bhn but I can certainly tell what hardness range my alloys and bullets are in. Not bad for less than $10.

  17. #17
    Boolit Master jlchucker's Avatar
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    believe it or not, H-grade pencils are used by some companies to test the hardness of their painted products. I was once a paint room foreman in a Stanley Tool factory, and 2H pencils were what inspectors used to do sample checks on painted products. These days such products are made overseas, and mostly of molded plastic-no longer painted.

  18. #18
    Moderator Emeritus/Boolit Master in Heavens Range
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    Quote Originally Posted by jlchucker View Post
    believe it or not, H-grade pencils are used by some companies to test the hardness of their painted products. I was once a paint room foreman in a Stanley Tool factory, and 2H pencils were what inspectors used to do sample checks on painted products. These days such products are made overseas, and mostly of molded plastic-no longer painted.
    I was a paint chemist (that is where I learned about hardness / art pencils. As a general rule, if you can scratch it with your fingernail, it's 'H' or softer. If you can't scratch it with your fingernail, it's '2H' or harder.

    Molly
    Regards,

    Molly

    "The remedy for evil men is not the abrogation of the rights of law abiding citizens. The remedy for evil men is the gallows." Thomas Jefferson

  19. #19
    Moderator Emeritus/Boolit Master in Heavens Range
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    Quote Originally Posted by acl864 View Post
    Picked up a set of 10 artist pencils for $8.50 in Walmart. It contained an 8B, 6B , 4B, 3B, 2B, B, HB, F, 1H, 2H, 3H and 4H.
    Tested a few things I had laying around just for grins.
    Egg sinkers I cast from lead sheet that I think is nearly pure lead- 8B
    Bullet I cast from Clip on WW- 3B
    Commercial bullet from Tennessee Valley Bullets (supposed to be around 12 bhn)- B
    Ingot of Clip on WW with 2% tin added- B
    Ingot of Commercial Hardball Alloy- F
    Commercial Rifle Bullet from Hunter's Supply- F
    Commercial Bullet from Meister- F
    Bullet I cast from clip on WW's and water dropped- 2H

    I'm not sure I can nail down an exact bhn but I can certainly tell what hardness range my alloys and bullets are in. Not bad for less than $10.
    Wow! I wonder what brand they are. Personally, I've never seen 8B lead, etc. But so long as you are consistent in how you use them, they will still let you reproduce your alloy hardnesses. But you might want to read the ASTM description (ask your library) of how to use them to test hardness properly.

    As an afterthought: Could you be rating your pencil tests by the softest pencil that will polish or scratch the ingot? If so, it would explain your very soft readings. The correct way of using the pencils is to find the softest pencil that will CUT INTO the surface. You should be able to see a tiny curl or chip of lead that is peeled out of the surface.

    The reason that tiny scratches or polishing of the surface are not reliable is that the composition of the pencil cores is not perfectly uinform: The process of mixing the clays, graphites, etc that go into each core hardness will leave tiny particles, much like mixing concrete will leave granules of sand. But by requiring that the core shave lead, you are testing the actual core hardness or strength, not some scrap of impurity in the clay that was used.

    Molly
    Last edited by Molly; 02-23-2010 at 11:57 PM.
    Regards,

    Molly

    "The remedy for evil men is not the abrogation of the rights of law abiding citizens. The remedy for evil men is the gallows." Thomas Jefferson

  20. #20
    Boolit Master jlchucker's Avatar
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    Quote Originally Posted by Molly View Post
    I was a paint chemist (that is where I learned about hardness / art pencils. As a general rule, if you can scratch it with your fingernail, it's 'H' or softer. If you can't scratch it with your fingernail, it's '2H' or harder.

    Molly
    Yup. Unless you've got a solid carbide fingernail like the inspector that used to come around to my department did on some days. I left him stumbling away puzzled one day when he came by and started scratching. I whipped out a number 2 pencil and he was totally befuddled when it didn't scratch paint. There's a difference between 2 and 2H and he didn't pick up on it.

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