Thursday, March 3, 2011

Home Made Lead Hardness Tester for Casting Bullets

Homemade Lead Hardness Tester (click on images for full sized view)

I bought a Lee Hardness Tester, and it was just too hard for my old eyes and shaky hands to use. So, I used what I had around and made one myself.

I have a 1/2 ton arbor press which is perfect as a starting point. Unfortunately, the mechanical advantage ratio was a PIA to calculate because my postal scale only goes to 5 pounds, and the force of the handle alone was more than that. I ended up using cast iron pipe on the back side to counter balance the weight of the handle and used a hanging pan on the end. I just added bullets until I got to the scale limit, and then weighed the bullets, and did the math. (all science is math).

I just checked the force using some better tools. I went online and bought a digital scale off of ebay. Check this out. The scale was only $3.97 including shipping, so I bought 2. I just checked, and they are now only $3.46. No wonder we buy so much stuff from china.

I needed a flat scale instead of a hanging one to measure the force of the scale, so I tool it apart and placed the load sensor assy under the press ram, and measured the force made by a 1 pound weight after I tared for the force of the arm alone.

It seems that the force mechanical ratio is about 18:1.

I ordered 5/32 and 9/32 chromium steel balls from Small Parts on Amazon (about $2-3 per pack of 25) .

The weight I use is cast from lead contaminated with zinc. It weighs more than my scale can measure, but back calculating produces a result of 128.5 lbs of force at the press (including the weight of the handle)

I use a bit of soft bullet lube to "glue" the ball to the test piece, then wipe it off and measure the indentation diameter with calipers.

I plugged the formula into my G2 cell phone, which has the QuickOffice spreadsheet included, and just plug in the indentation diameter and it gives me the hardness. I double checked with the Lee hardness tester, which I will sell. Since 5/32 is the size of the ball in the lee tester, I could use the spreadsheet to replace the chart Lee provides (which does not go below BH 7, so it can't measure pure lead)

I made the spreadsheet on my PC, then copied it to the MicroSHDC card on the G2.

Here is the actual spreadsheet formula entry

BHN = P / {pi * D * 0.5 * [D - sqrt(D*D - d*d)]}

P = the imposed load in kilograms (63.0 kilograms in our example, and it should be approximately one to five times D*D) (13 to 65 kg)
pi = 3.14159
D = the diameter of the ball in millimeters ( 0.143" or 3.63 mm in our example)
d = the diameter of the indentation in millimeters (0.177" or 2.9718 mm in my example)