Getting strange readings from a hardness tester

[rocketmann]

I just picked up a 1970's Wilson OUR3 hardness tester from craigs list. After I got the unit set up and calibrated to the test blocks I started testing everything that I had laying around. I had some cheap China blades that people had given me, a M tech 440 China blade, a Buck 110, a CRKT stiff Kiss and a ATS34 blade that I heat treated in my shop. I consistantly got readings in the upper 50's at the riccaso and other flat areas but 3/16" from the edge I would get readings between 45 and 52 for the same blades. I am using a 1/4" diameter spot anvil and the diamond penetrator. I can only assume 2 reasons for this.
1- My error in set up and wrong anvil for the job. or
2- Poor heat treating of all of the blades.

I am leaning towards #1

I also tested a Damascus Sigan Dubh from pakistan that some one bought online and wanted me to put a handle on that tested out at HRC 8-10 everywhere on the blade..
Any ideas on how to improve my testing would be great. I am always trying to improve my work.

 

[rocketmann]

Sorry for the trouble I found my answer using the search function. Feel free to comment though I am all ears.

 

[JBS TOOLMAKER]

Yeah, probably need a larger anvil. Are you holding some portion of the blade in your hand while it rest on the anvil ? Any movement or unbalance can alter results. Also if you are testing an area with profile( hollow grind ) there could be some spring action that will give false readings. The ideal situation is for the part to be balanced on the anvil....hands off, and checking on a flat surface.

 

[butcher_block]

any testing of a surface that is not in full contact or parallel to the anvil will miss read the hardness (think of it like it slips a bit as the test is running making all numbers low)

 

[Phil Dwyer]

Sorry for the trouble I found my answer using the search function. Feel free to comment though I am all ears.

What did your search reveal as the prob?

 

[silver_pilate]

I had similar issues when I picked up my hardness tester. Turned out to be not getting the test surface perfectly perpendicular to the penetrator. Angled surfaced like bevels are tough to test. Also, the more mass/stability on the opposite side of the penetrator, the more accurate the test.

With my particular tester, if the surface wasn't perpendicular to the tester, the penetrator actually couldn't penetrate fully because of the design. The penetrator protruded just a specific amount and needed to fully bottom out to get an accurate test. However, the surrounding tester housing would hit on the "up-hill" part of the tested material and stop full penetration.

(edited to add: that's officially the most number of times I've used the word penetrator or some derivative of it in a post )

--nathan

 

[rocketmann]

My search revealed that it is nearly impossible to get accurate readings on a bevel. It seems that the rockwell testing should be done on the flat surfaces after which you can use hardness files to compare the edge to the rest of the blade. I will be getting the test files this week. This testing will go along with what I have already been doing such as using a digitaly controled heat treat oven and the proper quenchant for my steel. I have been reading Kevins posts for years now and I am taking measures to remove any remaining variables in my process. I have a lot to learn.