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[Metrology] Accurate Rockwell Test for Homeshop

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Ray C

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#1
Folks,

I happen to have 3 methods of doing Rockwell testing. One is a stationary Rockwell tester; another is portable Leeb unit and the third is a plastic tube, ball bearing and a simple scale/chart. For items applicable to the simple unit, it gives results that are basically dead-on with the ones costing a couple grand each.

This only measures on the Rockwell C scale so, items need to be fairly hard for this to register. Also, the items should be at least 1/4" thick, must be flat, clean bare metal and must be supported on a heavy surface (such as the anvil portion of your work vise). Larger heavy objects can be measured provided there's a flat spot and the unit can be placed dead-on vertically. I've had this device for many years and it was store-bought but, I believe the manufacturer is out of business. It's very simple to make. See the picture and enclosed chart.

The ball bearing must be 3/16" chrome steel. There's a little lever that drops the ball inside the tube from a height of 25cm. As the ball drops and rebounds, the tube must be positioned so the ball does not touch the sides of the tube on the way down or up. Years ago, I made another one just like this with a wider tube and it worked just fine (but I'll be darned if I can find it now)... The tube is marked every centimeter and half-centimeter all the way up to the drop point. Don't try to drop the ball with your fingers. That will not work. It has to be dropped "cleanly" from a mechanism that just lets it go without influencing it. Look closely in the picture. That's what the little black lever accomplishes. Carefully drop the ball and watch how high it bounces and read the number. Use the chart and the sliding scale to look-up the Rockwell. Do multiple bounces in a row until you get 3 that read about the same. If you hear it touch the side of the tube, don't use that result. You'll get a feel for it after a while. Read the instructions on the chart...


IMG_20171231_211245.jpg

RockwellBounceChart.JPG

Have Fun!

Ray C.
 

francist

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#2
Ooh, I like that. I made an acrylic tube version a few years ago (I think it's called a sclerometer?) but didn't know how to come up with a useable graduation scale. Will have to dig it out again and try this version -- thanks!

-frank
 

Ray C

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#3
FYI: I can't over-emphasize that the ball must be chrome steel 3/16" diameter. The ball must begin it's clean free-fall from a height of exactly 25 cm.

I have a Rockwell tester with standards plates from 30 up to 60. They cost about 75 bucks each. The Leeb tester ran about $1500. This little plastic tube gives the same results on pieces suitable for it's limited application. The nice thing about it, is that it's non-destructive.

Regards

Ray C.
 

EmilioG

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benmychree

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Ooh, I like that. I made an acrylic tube version a few years ago (I think it's called a sclerometer?) but didn't know how to come up with a useable graduation scale. Will have to dig it out again and try this version -- thanks!

-frank
The commercially made unit, the parent of what you describe and picture is a Sclerescope; they were made just like what is shown, but much more elaborate, and the "hammer" is diamond tipped; they were made in the simple read by eye as to rebound, and another model that recorded the hardness number on a dial. They were beautifully made, even decorative --- I have both styles, although the recording dial type that I have does not work accurately, compared to the first type, and compared to my Rockwell hardness tester and it's test samples; it may be possible that the hammer may be damaged, causing the discrepancy in readings.
 
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benmychree

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Also, the hardness numbers taken by the Sclerescope are called Shore hardness numbers; it is not so easy to find a table that compares Shore hardness to Rockwell or any of the other hardness systems; one wonders if a competitive attitude on the part of the different hardness testing companies led to this??? I did find one chart that compares Shore with several Rockwell, Brinell hardness letters, tensile strength, Knoop, and Vickers hardness test numbers. This chart is in the form of a rotary sort of slide rule, made by the Pacific Transducer Co. (PTC) of Los Angeles Ca., and is called Model 655C. Click on the "full image" to see the whole picture. sclerescope 1.JPG sclerescope 1.JPG sclerescope 2.JPG sclerescope 1.JPG sclerescope 2.JPG sclerescope 2.JPG
 
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4GSR

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#7
There is a ASTM standard that cross references all the different types hardness readings including the Shore readings. I just don't remember the standard number.

BTW- I have two different ways of testing the hardness of a material. One is using hardness files. They are fairly accurate to use, but it takes an expert hand to read the files to determine the approximately hardness using them. My second method is based off of a "Teller Brineller" device. It uses a certified shear pin that holds the pin in a shear device. It is pressed against the metal surface by hand and hit with a two pound engineers hammer. The pin shears, and the penetrator leaves a indention on the surface like a "moon crater". The crater is measure in diameter with a 10x scope. That measurement is compared to that on a chart and Brinell hardness is given. Its good on materials with hardnesses up to around 495 Brinell or about 50 HRC.
 
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benmychree

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There is a ASTM standard that cross references all the different types hardness readings including the Shore readings. I just don't remember the standard number.

BTW- I have two different ways of testing the hardness of a material. One is using hardness files. They are fairly accurate to use, but it takes an expert hand to read the files to determine the approximately hardness using them. My second method is based off of a "Teller Brineller" device. It uses a certified shear pin that holds the pin in a shear device. It is pressed against the metal surface by hand and hit with a two pound engineers hammer. The pin shears, and the penetrator leaves a indention on the surface like a "moon crater". The crater is measure in diameter with a 10x scope. That measurement is compared to that on a chart and Brinell hardness is given. Its good on materials with hardnesses up to around 495 Brinell or about 50 HRC.
Yes, I have seen one used by the inspector in the shop where I apprenticed; it was used on a good sized forging that could not be handled by the Rockwell tester; the Sclerescope could have been used in its portable mode as I have also seen there, but the Brinell numbers were more appropriate to the job,
 

Ray C

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Also, the hardness numbers taken by the Sclerescope are called Shore hardness numbers; it is not so easy to find a table that compares Shore hardness to Rockwell or any of the other hardness systems; one wonders if a competitive attitude on the part of the different hardness testing companies led to this??? I did find one chart that compares Shore with several Rockwell, Brinell hardness letters, tensile strength, Knoop, and Vickers hardness test numbers. This chart is in the form of a rotary sort of slide rule, made by the Pacific Transducer Co. (PTC) of Los Angeles Ca., and is called Model 655C. Click on the "full image" to see the whole picture.
Very nice specimen. Is it functioning? Does the hand pump drive a vacuum chamber or, is that to release the projectile?

As for the many types of hardness testers, I remember my father (tool and die maker) and my uncle (metallurgist) having long discussions about that topic. I took an interest in metallurgy myself and it seems traditional folks have all settled on Rockwell, Vickers and Brinell. Several years ago, I purchased a series of professional heat-treating reference books (running about $350 each) and all specs are given as Rockwell, Vickers and Brinell. I believe it turned-out that Shore is still commonly used for durometers. Some years ago, I was a director of engineering for a medical device company and all the plastics were measure in Shore values.

I like the Leeb tester the most. I have a Cimetrix brand. Portable, accurate and it gives read-outs in any/all scales.

Ray C.
 

benmychree

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Very nice specimen. Is it functioning? Does the hand pump drive a vacuum chamber or, is that to release the projectile?

As for the many types of hardness testers, I remember my father (tool and die maker) and my uncle (metallurgist) having long discussions about that topic. I took an interest in metallurgy myself and it seems traditional folks have all settled on Rockwell, Vickers and Brinell. Several years ago, I purchased a series of professional heat-treating reference books (running about $350 each) and all specs are given as Rockwell, Vickers and Brinell. I believe it turned-out that Shore is still commonly used for durometers. Some years ago, I was a director of engineering for a medical device company and all the plastics were measure in Shore values.

I like the Leeb tester the most. I have a Cimetrix brand. Portable, accurate and it gives read-outs in any/all scales.

Ray C.
Yes, this one is functioning; the rubber bulb both raises the projectile to the catch and when squeezed again, releases the catch; the other one that I have which records the reading on a dial functions, but is not accurate, I found them both on E Bay.
 

Vacuum

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4gsr would you be willing to give some guidance on using the file test. I understand what the directions say but what is your first hand take on using the file testing process verses the testing devices.
 
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