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
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
Staedtler hardness rating
Molly said: "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."
Right on, Molly. I suggest we adopt the above as a best practice for testing lead alloy hardness with standard pencils. Start by flattening a small section of the alloy surface with a file. The base of a large caliber bullet is sufficient. Prepare the pencil by sanding a small flat or "meplat" on the tip of the pencil with 400 grit sandpaper. Then hold the pencil at 45 degrees, as if writing, and press firmly down and forward with the sharp edge. If the pencil skids over the alloy surface, even if it leaves a slight scratch, its still not harder than the lead alloy.
Work your way up to progressively harder pencils, until you get to one where the sharp edge of the pencil "meplat" really digs into the surface, pushing up a curl or mound of alloy in front of it. At that point you stop and consider the hardest pencil that will not dig into the alloy in this manner, to be the "Staedtler" rating of the alloy in question.
For example, my little store of 1in20 (tin-lead) alloy skids on a 3B but digs in on a 2B, therefore its Staedtler hardness is 3B. Some Hornady swaged lead bullets I have will skid on 4B but dig in on 3B, therefore the Staedtler hardness rating is 4B. I also suggest we stick to the Staedtler Mars Lumograph pencil sets, since the maker claims they conform to ASTM standard D-4236 for consistency. They are cheap and readily available at Office Depot and other stores.
With this method you can quickly determine the Staedtler hardness of a given alloy and begin to gauge which alloys are best for your loads and firearms. While its possible to roughly equate Staedtler hardness ratings to Brinell hardness numbers, that question is moot, so long as you stick to the pencil method for testing all your alloys. - CW