Is BH linear?

[ETG]

Had an idea for a poor mans BH tester. 1' section of tubing with a piece of steel round stock pointed at approx 135* that is 3-4" long (was thinking 1/2"). You could put a mark on the plunger and reliably align it to the top of the tube. Put tube against lead - hold plunger with mark aligned with top of tube - drop plunger and measure the indentation. Just don't know if you could use pure lead and a sample of known hardness and then interopolate for values in between.

[grumpy one]

BHN is the yield-stress of the alloy, measured in metric units. It is therefore based on the cross-sectional area of the indentation, not its depth or diameter. (However the area is proportional to the diameter squared, which is the way proper BHN measuring devices go about determining hardness. The Lee hardness tester actually applies correct BHN theory, unlike most other hardness testers.) Using a pointed indenter rather than a spherical one is also technically incorrect; it may cause stress-concentration effects.

Another problem with your device is that it does an impact test, not a hardness test. BHN measurement requires that a specific, perfectly constant load is applied for a minimum of 30 seconds.

[rob45]

Using a pointed indenter rather than a spherical one is also technically incorrect; it may cause stress-concentration effects.

Another problem with your device is that it does an impact test, not a hardness test. BHN measurement requires that a specific, perfectly constant load is applied for a minimum of 30 seconds.

+1 on that statement. Were one to send a sample to a lab to test for BHN, the report sent back should usually specify the time involved during the load test.

For a homemade tester, I believe the most accurate method is using the reloading press you already have in conjunction with a bearing and weight on the handle, providing 1.)you can precisely identify your press leverage, and 2.)accurately assess the weight hanging on the handle.

Here is a link where the person does exactly that; he uses a die in the press, while I use a long-thread bolt. The handle must be kept level, so the bolt allows more flexibility when testing various length samples.
http://www.mountainmolds.com/
Go to "Articles and links", then click on "Home-made hardness tester".

This method is extremely accurate; I have compared it to "professional testers" costing over $1500, and it is "spot on". Anybody on this type of forum has access to a reloading press.

[Zbench]

Guys,

You should watch the local listings and FleaBay for a used Wilson Rockwell Tester. Used ones with complete weights can be had for sometimes less than $100. While the dial is likely jacked up, you don't really need it for a BHN test. What is does for you is apply very accurately a known force. Once that is done you measure the diameter just like the Lee and calculate BHN. Just a thought for folks who are struggling with tired springs and other inaccuracies.

Pete

PS. You need a Regular tester, not a superficial tester. Regular testers can apply 60, 100 and 150 KgF loads (read as Kilogram force).

[Casting Timmy]

I think it could work as a hardness tester, but it would be more like a finger nail test. It would give you great results, but you won't really be able to relate hardness with other people. That's the real reason the test is defined the way it is, so everyone can relate there measurements to each other.

You might be able to relate hardness with others after a while of doing some testing. There are some people doing hardness tests using staple guns and measuring how far the staple goes in. Also long as you get a consistent drop, you should be able to get a comparable result to other samples.

[Duhawki]

Yes Brinell is roughly linear with respect to tensile strength. Rebounding indentor hardness testers are not a new idea, but existing ones work by measuring coefficient of restitution as hardness rather than by measuring depth. Depth of penetration is the basis for all Rockwell tests. Rockwell scales that use a 120 deg diamond conical indentor are almost as linear as Brinell. The Rockwell ball scales such as "R", which is used for lead, are much less linear.
Regards,
Duhawki

[JIMinPHX]

That gizmo will not give you official Brinell numbers, but it is probably good enough for you to compare the relative harnesses of different batches of lead so that you can blend them to produce something that you can shoot consistently.