Calibrating Hardness Tester, need known hardness material

[cbrick]

BHN is a relative moving target and is not easily calibrated to.

Very good statement and quite true. One does need a sufficient sample size (number of tests for each alloy). I usually do 3 test on a bullets/ingots of an alloy which gives a fairly good idea but if I really, really want to know I use 10 tests per alloy. The average gives a very, very good idea of the BHN then. Doing just one test on a single bullet/ingot might put you in the ballpark but that's about it. Larry Gibson

Exactly! Just as with a chrono test, one shot over the screens tells you from very little to nothing about either velocity or consistency. A 10 shot chrono test averaged will give you a reasonably accurate idea of the particular lot, same with BHN testing.

Rick

[rattletrap1970]

Took out the hex wrench at the suggestion of Dusty.. Now it uses the ratchet wrench from the Lube sizer (which are avaiable from Lyman for $8)
I figure the best sample for testing (on my end) would be actual bullets that someone cast from "Dead soft" up to the hardest thing they could make. Then bagged and on the bag written their hardness based on an average of ten tests per bullet. If I then did the same 10 tests and averaged MY results I think I'd have a pretty good tester. Like I said, this more of a design project than anything else.

[dikman]

I like the ratchet handle, but will the "stop-start" of the ratchet action affect the penetration of the point when screwing it in? I have no idea if it's critical to have a continuous pressure applied during this part of the process. As to the point, the idea of a bearing is nice. I already have something that might work, although it's a little oversize (it's off a wood-turning lathe). I might have to look into it, as my point is slightly off-centre. It works, but it annoys me. I drilled and tapped the end of the threaded rod to take a screw-in hardened point, but no matter how much I tweaked it I just couldn't get it exactly centered in the 4-jaw chuck. Also, the angle of the point will make a difference, as I feel that mine may need a bit more of an angle on it. I tried a blunter, rounded-off point, but wasn't happy with the readings, as it gave less spread to the figures.

This is all most interesting.

[rattletrap1970]

I was thinking of the stop-start issue. The only other way that I can figure is to have a sliding spring loaded indenter. So, you'd slide up to sample, then roll a lever over loading a spring. Kinda like an actual Rockwell hardness tester. Personally for best results I think just having the knob at the edge of a bench or table and giving it one nice complete turn might be easier.

[dikman]

Yep, I reckon that'll work. A great idea about the bearing mounted point, btw . I just modified mine to try it out and it works great. Mine is, of course, considerably oversize compared to your drawing, but that doesn't really matter. It's smoother to wind in, and I think your large knurled knob should be fine, as I could give it one turn just by gripping and turning the threaded rod. You'll need clearance to turn the knob, either by mounting the device on a block of some sort or, as you say, using it at the edge of the bench.

I might make a knurled knob for mine sometime (out of brass, maybe - I like turning brass).

[rattletrap1970]

McMaster Carr sells them. In different materials.

Yep, I reckon that'll work. A great idea about the bearing mounted point, btw . I just modified mine to try it out and it works great. Mine is, of course, considerably oversize compared to your drawing, but that doesn't really matter. It's smoother to wind in, and I think your large knurled knob should be fine, as I could give it one turn just by gripping and turning the threaded rod. You'll need clearance to turn the knob, either by mounting the device on a block of some sort or, as you say, using it at the edge of the bench.

I might make a knurled knob for mine sometime (out of brass, maybe - I like turning brass).

[dikman]

The postage to Oz would probably cost more than the knob!! Besides, I like making things......

[bangerjim]

Since you have a lab tester would you be able to send me a few boolits from softest to hardest with your reading if what they are? Since the tester itself doesn't really change in design, the only thing that changes is the cross reference sheet based on my numbers vs. yours.

I use a Cabine for lead. My other unit does NOT go down that soft. That is why I bought the Cabine!

banger

[dikman]

I found a knurled wheel in my lathe bits drawer, turned out to be a perfect fit on the threaded rod! And it turns real easy. I think I might replace the nut with a circular wheel with indent markings on it next.

Then one day I may even paint it! Attachment 90467

Just had a thought - a collar in front of the knurled wheel, with an extended locking screw. Set it so that when the point is just touching the sample under test the extended screw is touching the far side of the indicator rod. Then turn the wheel until the screw touches the other side of the rod. No need to bother with lining up the indent mark with the pointer, just do it by feel. It's not quite a complete turn, obviously, but that shouldn't matter as long as it's consistent from one test to the next.

Thoughts?

[rattletrap1970]

Thinking something like this. Threaded collar with a pointer on it. Turn knob in till it touches one side of a finger or pin that juts out from the body of the unit. When you turn the indentor load the collar makes one revolution and touches the finger again (on the other side). The finger on the unit and the finger on the collar can be machined in such a way to correspond with the travel of one turn (2 steps on both fingers) so they line up on the same plane.

[dikman]

I just tried the "rotating pointer" idea. I tapped a hole in the nut in front of the knurled wheel, and fitted a machine screw with a wingnut loc-tited at the head end (to use as a "handle"). I screwed the nut up to the mounting, then backed it off about 1 1/2 turns. Put sample in place, screw the point in 'til it just contacts the sample, rotate the nut and screw against the right of the pointer rod, tighten screw and then turn knurled wheel until the set screw contacts the pointer rod on the other side. Easy.

Using your idea, I should be able to replace the pointer rod with something with an off-set in it, so that as the nut rotates the set-screw slots into a recess and allows a full rotation of the main screw.

A little more fiddling, perhaps, than just looking at the markings on something, but a lot more consistent.

Next thing is a very light coil spring in front of the nut to hold it against the pointer rod when it's not tightened up.

[rattletrap1970]

I'd love to see a photo of that.

[dikman]

Ok, how's this? Even Though the main screw is a fairly coarse thread, one rotation isn't enough to allow for an offset, so I filed a groove in each side of the brass rod so that I could get as close as I could to full turn (between 350 - 355 degrees, I reckon). Doesn't really matter, as the main thing is repeatable consistency in each test. My idea of a coil spring in front, to hold the set-screw upright didn't work - yet).

[Grump]

Back to the calibration question...

How reliable are solder bars?

At the extreme, you could consider solid tin. I would shy away from pewter because it's not that "standard" an alloy.

You also seem ambitious enough to perhaps rig up some electroplating--with the correct solutes, you could get pure lead to calibrate the bottom end of the scale, but that is a lot of trouble compared to buying some.

I could send you some of my stuff with notes of where it falls with the SAECO tester...

[rattletrap1970]

That's what I mean, if someone has a tester the trust and could test samples of their own (like 5 hits or so on each sample and average them), then send me the tested samples with YOUR readings on the Baggie(s). Then I could test them and compare my dial numbers to your numbers. Once I had a bunch of samples, then I'd make a custom dial.