Testing for BHN is rather simple - in theory.
you push the correct size ball bearing into the sample with a known amount of force and measure the diameter of the dent.
Then put the measurements into a formula and calculate the value.
My home shop technique is to place a bathroom scale on my mill table and use the crank on the quill to push a ball bearing into the sample. The mill has a crank down quill, rather than a lever like a drill press, so its easy to control the load and keep it constant at about 100 pounds.
The tricks are
1) find the table with the correct load and ball diameter for lead. Google will usually find the tables for cast iron and steel. If you use those balls and loads your likely to drive the ball right through your sample.
2) use a ball very close to the nominal diameter for the scale you're working with- the math indicates you can use any ball, but if you run the test with different balls, you will get different hardness values. on the same sample.
3) Accurate measurements of dent diameter are critical. I use a set of calipers and a microscope to get it right.
Play with the math and you will find that the output is rather sensitive to diameter.
4) I plotted a graph of the dent diameter vs BHN with notes on load and ball size. That way I don't have to fuss with looking up everything and doing the math down in the shop when a wild hair strikes me and I decide to test some lead.
I cast up ingots from unknown scrap, test a bar and stamp my value for BHN in it with letter and number stamps.
I often also punch in an H or S to help keep it sorted.
So, does it work - kind of.
I used a melt of commercial round balls for a reference standard to see if my numbers were realistic, and they were not spot on to the textbook, but they were close.
I can get a value on a bar that repeats to 0.2 BHN without much trouble, and corelates well to published values for known alloys.
Thats good enough for me. I am not that fussy. I just want to set the dead soft stuff aside for muzzle loaders, and get the rest to a reasonable hardness for black powder cartridge guns or handguns.
At some point I need to go back and test the bars after they sit on the shelf for a year or two and see if the value changes. In some alloys it will. The melting point of lead is about twice room temperature when you start from absolute zero. Half of the melting point when measured from absolute zero is not unreasonable for tempering or aging of most alloys. Don't assume anything other than pure lead has a stable hardness unless you check.
Could my technique be improved. Sure.
I could find a ball of the exact nominal size, not just fairly close. That would help.
I could improve the accuracy of the dent measurement by taking more samples
Making a mold to give a standard reference sample thickness and size and finish on the test surface would improve consistency.
Could I build a lever and weight system that applied a constant load by gravity, rather than try to get to the desired number by watching a bathroom scale that may or may not be well calibrated. Sure.
you push the correct size ball bearing into the sample with a known amount of force and measure the diameter of the dent.
Then put the measurements into a formula and calculate the value.
My home shop technique is to place a bathroom scale on my mill table and use the crank on the quill to push a ball bearing into the sample. The mill has a crank down quill, rather than a lever like a drill press, so its easy to control the load and keep it constant at about 100 pounds.
The tricks are
1) find the table with the correct load and ball diameter for lead. Google will usually find the tables for cast iron and steel. If you use those balls and loads your likely to drive the ball right through your sample.
2) use a ball very close to the nominal diameter for the scale you're working with- the math indicates you can use any ball, but if you run the test with different balls, you will get different hardness values. on the same sample.
3) Accurate measurements of dent diameter are critical. I use a set of calipers and a microscope to get it right.
Play with the math and you will find that the output is rather sensitive to diameter.
4) I plotted a graph of the dent diameter vs BHN with notes on load and ball size. That way I don't have to fuss with looking up everything and doing the math down in the shop when a wild hair strikes me and I decide to test some lead.
I cast up ingots from unknown scrap, test a bar and stamp my value for BHN in it with letter and number stamps.
I often also punch in an H or S to help keep it sorted.
So, does it work - kind of.
I used a melt of commercial round balls for a reference standard to see if my numbers were realistic, and they were not spot on to the textbook, but they were close.
I can get a value on a bar that repeats to 0.2 BHN without much trouble, and corelates well to published values for known alloys.
Thats good enough for me. I am not that fussy. I just want to set the dead soft stuff aside for muzzle loaders, and get the rest to a reasonable hardness for black powder cartridge guns or handguns.
At some point I need to go back and test the bars after they sit on the shelf for a year or two and see if the value changes. In some alloys it will. The melting point of lead is about twice room temperature when you start from absolute zero. Half of the melting point when measured from absolute zero is not unreasonable for tempering or aging of most alloys. Don't assume anything other than pure lead has a stable hardness unless you check.
Could my technique be improved. Sure.
I could find a ball of the exact nominal size, not just fairly close. That would help.
I could improve the accuracy of the dent measurement by taking more samples
Making a mold to give a standard reference sample thickness and size and finish on the test surface would improve consistency.
Could I build a lever and weight system that applied a constant load by gravity, rather than try to get to the desired number by watching a bathroom scale that may or may not be well calibrated. Sure.
