Does anyone know how to calibrate a RC hardness tester?

Tom Lewis

Tom Lewis

Joined
Feb 24, 2000
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I have a hardness tester I bought from Harbor Freight maybe 20 years ago. I have the instruction manual and also the test blocks that came with it. The tester is off maybe five points from what the test blocks read.
The manual does not tell how to adjust the tester. It just tells how to use it and how to check it with the test blocks.
I have looked on line for re-calibration instructions but have not been able to find any. There are lots of Youtube videos and some claim to show how to calibrate a hardness tester but all they show is how to use it.
In the back of the tester is a oil pot with a screw on top. Maybe this is the way to adjust the tester. I would like to know for sure before I start changing things.
Any help will be appreciated.
 
I'm assuming this is a bench top model (which I know nothing about)? The portable ames style can be adjusted slightly by rotating the dial indicator or adjusting your eyeline.

If your getting consistent results on a known material hardness (ie you know how much it's off by) over a range of hardnesses then it doesn't matter too much but I can see where you'd like to have the number reading properly.

I didn't harbor freight sold these.
 
Is it one of the HR-150 cloned? Download a HR150 manual and see if it looks the same.

Do you have a photo to post?
 
I bought this from Harbor Freight back in 1996. It does read the same each test, but of course I would like to be able to adjust it so it reads the same as the test blocks. You can see from one of the pictures that the dial is slanted to the left instead of being straight up and down. I do have the owners manual but don't see where it tells how to adjust the tester.
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The tilted dial may be the calibration means. A lot of dial indicators are calibrated that way. It looks funny, but it works.
 
Adjusting the HR-150A hardness tester following the instructions on the directions below works like a champ. In figure 7 below you can the 3 main calibration screws, #5 is the center with a lock nut, the two outside silver screws do not have lock nuts. The center screw with lock nut adjusts the pointer needle.
calibration-image.png

1: If the Pin End of Small Level is not locate in the middle of hole of as shown in Figture 8, loosening the Screw# 1&2 in Figture 7 and moving the bar right or left to make the Pin End of Level in the middle of hole as Figture 9, then screwing it down. This position might require adjusting the pivot pins holding the center bar. This step should only be required in a badly out of calibration tester.

2: With the main dial in front turned so the “C” (call this the “zero” position) is exactly at the top 12 O’clock position. Note position of needle on main dial, is it somewhere between 11 and 1 O'clock? If so, proceed to step #3. If not, use a 7mm wrench to hold lock nut on center screw (#5), hold screw with screwdriver and loosen nut with wrench. Playing with this screw the needle can be adjusted easy between 11 and 1 O'clock. That's close enough for now.

3: Take the ~62 Rc test block and take a reading, note if reading low or high. Here I then take a 1/4" or 3/8" HSS tool bit (from lathe) and test it. Note how it reads compared to test block. Use this HSS tool steel for most of testing to save many dimples in test block. The HSS steel should read somewhere from 62 to 67 Rc depending on metal.

4: If reading is low, loosen the two outside silver screws and move plate forwards toward dial a small tad. If reading is high, then move plate backward a tad. Small movement will make a fairly large difference in calibration. After tightening the two outside screws, the big needle will again need adjusting with the center screw to somewhere between 11 and 1 O'clock.

5: Test HSS steel again. This does take a good bit of playing around to get correct. With calibration set at 62 Rc, I found my low end still didn't read correctly, but that's not a real problem since I only use that for testing backsprings and that reading isn't as critical as the blade - in my opinion anyway.

6: Once the calibration is complete, the needle on main dial should be adjusted to the 12 O’clock position, and with the test result reading Rc value of test block.

This procedure works for me. I'd be interested in hearing if it works for other folks.

Ken H>
 
I have the same tester, not really working right for several years now, gathering dust. Y'all gonna make me fix it with detailed instructions like that, lol.
 
https://www.bladeforums.com/threads/grizzly-rockwell-hardness-tester.1697329/

Tom Lewis said:
I have a hardness tester I bought from Harbor Freight maybe 20 years ago. I have the instruction manual and also the test blocks that came with it. The tester is off maybe five points from what the test blocks read.
The manual does not tell how to adjust the tester. It just tells how to use it and how to check it with the test blocks.
I have looked on line for re-calibration instructions but have not been able to find any. There are lots of Youtube videos and some claim to show how to calibrate a hardness tester but all they show is how to use it.
In the back of the tester is a oil pot with a screw on top. Maybe this is the way to adjust the tester. I would like to know for sure before I start changing things.
Any help will be appreciated.
Click to expand...
 
Thanks to everyone for the help. The instructions were what I needed and the video also really helps. The manual I got with the tester was translated from Chinese to English by someone who was not very good at English. Also I don't see anything in my manual about adjusting the tester.
So, THANKS!
 
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