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Accu-test HRc tester


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So some may or many not know who I am and what I do.. 

I started forging back in 78 starting out with knife and sword making..  Since that time I have done such a variety of work with different steels and the subject of hardness comes up all the time. 

The reason for this and the following posts is I am in the process of putting up a teaching center and frankly many really don't understand the process of what Heat treatment is and how it is applied for a given item for a given carbon content or alloy. 

To help students along I purchased several Rockwell testers to show how the relationships of carbon, and other alloy agents playing out with the included tempering process and by having hard numbers can help others while in that teaching environment to bring common sense approach home to their own shops with a better understanding of why and how without the equipment.. 

I'm starting this in order of simplicity and of overall usage.. 

This particular tester is useless for nearly all blade related work but is great for other items that are at least 1 inch thick.     With this said.. It can be used for blade edge work if using stock removal or if using to work out a test measure of max hardness and then temper hardness.  but the metal has got to be at least 1" thick (IE tall).. Which means standing up a blade so you are working directly on the cutting edge.. I find this easiest to put the piece in the vise and have the material completely scale free.. 

For all testers the metal has got to be clean and oil free. 

This particular tester just have a ball that falls and bounces.. The height of which shows hardness. 

The problem with this tester is it needs to be exactly vertical and the item used on must be flat faced so the ball has a direct contact patch and no moving the tester while in use. 

This test involved a Refflinghaus anvil,   and a wrought iron hammer with 5160 steel face and peen which has been radially tempered..  

The anvil is over 64HRc and the hammer 61 Hrc in the center and 55 towards the edge/corners. 

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Edited by JenniferP
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The reading that you were getting on the anvil and hammer seem to be a lot higher than I would expect for those tools.  I had a similar instrument and the problem that I had with it is that the bottom of the tool made too tight a seal to what was being tested and air pressure built up under the ball.  I would go with the tester that John showed if I had deep enough pockets.

 

Doug

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Doug I've tested it against test samples and it accurate for what is shown.    The Refflinghaus is guaranteed at a minium 59HRc or harder and the 5160 used in the hammer face as hardened can be as high as 62HRc.  And this is left untempered.:) 

Is it a great tester.. I don't know.. It is handy though and many have never seen one.  (also from a lay persons stand point, everyone is told to drop a ball bearing on an anvil when buying it for a rebound test this at least shows them a round about why).

It's a tester..  No tester should be taken as accurate unless you can verify the results.  Also common sense is a priceless tool.. :)  Not sure how you got air trapped as there is plenty of clearance in this unit?  Its and interesting concept of air trapping though.. 

I paid 40.00 for it and is handy for a simple test.. 

This is tester number 1.. Listing them in order of simplicity.

 A scleroscope is a device used to measure rebound hardness. It consists of a steel ball dropped from a fixed height. The device was invented in 1907.

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We have a very advanced unit that works on a similar principle at work.  Metallurgically, I hate these things with a fiery passion.  The definition of hardness, as far as material science (including metallurgy) goes, is "the resistance to localized plastic deformation" (Wikipedia gets it right).  A rebound does not test this, and they never have and never will.  Rebound tests can be useful and can definitely tell you some useful information.  If you have an appropriate sample of metal (this is not very common) then you can indeed correlate the rebound to a hardness.  The problem lies in different materials having different rebound rates for similar hardnesses.  There is also problems with harder materials being accurate.  We make steels and high chrome white iron (HCWI) that are often above 65 HRC.  We need to use a different calibration for steel vs. HCWI.  I've also had big problems with oil quenched and tempered 8630 reading higher than as quenched 8630 can get (a later Brinell test confirmed that the rebound tests from our vendor and our in-house test were very wrong).  

 

Sorry.  These things are a bit of a trigger for me.  They are a qualitative tool, not quantitative.  If they were just labeled as "% rebound" rather than as a hardness I would be happy with them rather than irate.  

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2 hours ago, Jerrod Miller said:

 

So true.

 

 

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Jennifer’s, I am one who is really pleased you’ve shown this. Is $40 a average price or did you get a deal? This would come in handy to tes t and prove any commission knife made is what it states. Yes, by experience we can tell whether we’ve finished “close” to the hardness treatment should produce, especially running other performance testing or meets criteria for the job intended. This can approve or disprove otherwise.

best regards, Gary LT 

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16 hours ago, Jerrod Miller said:

 The problem lies in different materials having different rebound rates for similar hardnesses. 

 

There is also problems with harder materials being accurate.  We make steels and high chrome white iron (HCWI) that are often above 65 HRC.  We need to use a different calibration for steel vs. HCWI.  I've also had big problems with oil quenched and tempered 8630 reading higher than as quenched 8630 can get (a later Brinell test confirmed that the rebound tests from our vendor and our in-house test were very wrong).  

 

Sorry.  These things are a bit of a trigger for me.  They are a qualitative tool, not quantitative.  If they were just labeled as "% rebound" rather than as a hardness I would be happy with them rather than irate.  



You bring up some very interesting points.. 

Non Destructive testers are really neat with no deformation at all of the surface..  Your lucky to be able to work with such items. 

Metallurgy on a whole is very interesting and can see why you feel the way you do and your point about  " Hardness"  and "rebound rates" being different for different materials of the same Hardness is a great point.   

 

 

7 hours ago, Gary LT said:

Jennifer’s, I am one who is really pleased you’ve shown this. Is $40 a average price or did you get a deal? This would come in handy to tes t and prove any commission knife made is what it states. Yes, by experience we can tell whether we’ve finished “close” to the hardness treatment should produce, especially running other performance testing or meets criteria for the job intended. This can approve or disprove otherwise.

best regards, Gary LT 


Gary,   I'd say it was a deal..  But with this said..   they stopped making them some time ago so not easy to come by.  (ebay find after a friend of mine purchased one).
 

This type of tester really needs to be looked at for what it is and I would not call it's results as accurate for lab results..   In other words showing how it works and then someone understanding the premise behind it was more the idea of this post. 

Metallurgy and hardness can be a tricky slope depending on "what ones thinking is" and there are standards in place that many agree with and others do not.. 

As Jerrod Miller pointed out.. You can have 2 different metals of the same (hardness) but show different rebound..   The subject can get very deep. 

With this said.. there are options out there @john marcus pointed to, as well as so many others depending on budget that will give better, more accurate readings which can be documented.

I've been doing this for over 40 years and don't need this to test for "How hard" something is based on metal used. After awhile you get a feel for the "About" hardness.  but it does give a down and dirty speculative hardness if used against a known test target of that very same material and you want to have fun with your buddies.. 

I own 3 hardness testers and really should at some point evaluate this tester more just to see the limits it has.. 

The only requirement stated for the test subject is flat, clean and  1" thickness.   So from a finished knife blade perspective it's useless. 

It has been accurate on the items tested and against 1 other tester (Ames 2200)..  Doing the testing in reverse..   Use this drop tester and then test again with the Ames tester.  The results were the same reading.  Which of itself is interesting.   
 

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