HRC testing

C

charles brown

Joined
Aug 3, 2007
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3
so how does one do rockwell testing. or does it even matter if im just trying to make a knife out of a file for myself.

ps. i really like mykulmorris's knives and thats what spurred me on to actually trying to shape one for myself. well that and not having $75 to buy one of his.

oh and for the thread that i read the other day about angle grinders. i annealed the file in a coal fire in the back yard. drew a general shap on the knife, used a dremel to cut that rough shape and have used a file since then to remove the rest of the material. now that im using the file correctly, its going much better.

thanks everyone for the tutorials youve put up here for us n00bs.
 
I've only known of machines to do the testing, and the rough estimate of the file scratch tests
 
Rockwell testing is done with a carbide punch on a machine and measured with a microscope that has a scale built into it (I think that's what I read). It's not something you can do at home. And no, I wouldn't really worry about it if you're just messing around and making a knife out of a file. This forum is awesome and if you stick around you'll learn a LOT. Welcome.
 
Using the punch and microscope is a Brinell hardness test. You measure the diameter of the punch mark in your test sample to determine penetration of the indenter. Softer materials end up with a larger indention. You can actually get these for home or field use. I had a machinist bring one of his up to the clinic for me to check out. Pretty nifty setup. They use a calibrated spring punch so you get roughly the same force each time and have a field magnifier that can read hardnesses within a couple of points. It gets you in the ball park at least.

True RC testers are typically desktop units and cost $800 and up with the sky the limit on price. I did see a unit that you could mount in a bench drill press chuck, but it was pricey as well.

Here's an interesting page with many different types of testers. They have a Brinells unit like the one I was shown that claims accuracy of +/- 1.5 points in the RC scales. Also, they have the hardness testing files that many use for a rough idea. I bet you could find a portable tester of the Brinell's type for a reasonable price, though the stuff on this page is a bit pricey.

http://www.flexbar.com/PDF/General/057-bench top hardness tester.pdf

If you have a local machine shop handy, they almost assuredly have a full size high quality RC testor (at least if they do serious industrial work). They may agree to do testing for you for a minimal fee.

--nathan
 
You put the diamond penetrator into the machine. Set the machine to 150kg for the C scale.

Put your blade on the anvil and raise the anvil screw until you make contact with the diamond point. Continue to raise the screw to pre-load the machine. It's typically three full rotations of the big dial and a small dial will register as well.

Pull the release lever, wait until the unit quits moving. Push the lever back, and the needle will point to your C scale hardness.

Easy as pie. :)
 
Very expensive pie. Damn you Nick and all your fancy toys! :mad::grumpy::(

J/K. Soooo....when we gonna see that finished WIP knife that's been hanging over our heads for the last decade (or so it seems)? ;)

--nathan
 
OK gents... I realize we all have a fascination with understanding as much as we can about our steel. But seriously, is a hardness reading all that important?

I know a little about testing blades, performance-wise. I use the brass rod test (not useful for heavy blades/thick edges, I know), whittle some old nasty hickory, whack the spine hard on my vise (I know, that's not the same as smacking on a good anvil) to see if it breaks or the spine chips, I cut cardboard and newsprint and cigarette paper, shave my ankle (yeah yeah, don't laugh, I have almost no hair on my arms anyway)...

From a customer's point of view, isn't that more meaningful than an RC number? Hardness alone doesn't mean everything.

A $1000+ hardness tester seems a bit unnecessary to me, although it does seem like a good idea to have a machine shop check the occasional blade. I doubt that would cost a whole lot.
 
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HRC numbers are just that: numbers. It's just another measure. Just another check. Your real life testing is just as valid, if not more so. Where HRC's come in handy is to see, numerically, if you're achieving what you want to from your heat treatment as far as hardness, or lack there-of, goes.

--nathan
 
That seems reasonable, Nathan. Maybe I should spend some time with the Yellow Pages and find a machine-shop that will Rockwell test for me... maybe one blade from every ten, or something like that. I don't see it being necessary for every single blade, though.

Don't get me wrong guys, I'm all about quality control/quality assurance.
 
If you heat treat consistently, you could just use one out of each batch, and consider that number for the whole set.
 
Yeah, that's what I'm thinking, Mike. My oven is on the way (I'm like a little kid the week before Christmas) so with a little guidance I hope to learn to HT consistently.
 
I think some Customers NEED to know the hardness of a knife, just like those Customers NEED to have the blade heat treated by Paul Bos.

I think an RC tester would be useful to learn how to heat treat better and take it step by step if you were tempering a blade down to lower and lower hardnesses.

Perhaps it also shows the customer that you 100% test your knives you send out as well. like the Pros do i'm sure.
 
I test every blade I make. It not only helps with consistency and predictability, which is a must with slipjoints. It also helped me diagnose a faulty thermocouple in my furnace. I was unknowingly getting inconsistent temperatures that caused some blades to be 6-8 points softer than normal. I changed out the thermocouple and back up to full hardness they went.

Ask around at the knife shows. Last year I picked up an older Wilson Rockwell tester that works very well for $350. They’re out there you've just got to look.
 
Hi,

Here you go, Testing Files.

The only method cheaper is ringing the part. Tapping it and listening to the sound. You can get pretty darn close with just that but takes practice.

dalee
 
dalee100 said:
The only method cheaper is ringing the part. Tapping it and listening to the sound. You can get pretty darn close with just that but takes practice.

dalee
Click to expand...

I wonder if they have a set to help you compare hardnesses
 
HRC is indeed only numbers that when taken on their own with no other information will tell you very little. Penetrative hardness is but one piece of the puzzle but it can be a very valuable piece in seeing the entire picture when combined with other information. Files also measure hardness but a different kind of hardness (scratch not penetrative) and are thus as much if not more limited than HRC alone. Put the two together and now you have much more of the picture to make something out of. As has been discussed many times here before the brass rod test or other homegrown methods of analysis often have the serious draw back of not defining what property is being actually tested (cross sectional elasticity or heat treatment??). To test the knife itself it seems to make the most sense to just put the knife to hard use in a ways that it will eventually be used.

Rockwell, files and other measures of specific properties really are not a test of a knife, they are a test of some the processes in making a knife. If you have everything correct and controlled enough in your heat treat to say that you expect a 60HRC reading and then test it out at a definite 60HRC, this is giving you invaluable information on your heat treating procedures. If the test is off by several points, you know something is wrong and need correcting (even more invaluable information), but the draw back is that the Rockwell test alone will not tell you what is wrong, only that there is a hardness problem. Just one example of another drawback of using only Rockwell numbers is that large grained steel will actually achieve greater hardness with ease, so really fantastic HRC numbers may not be a good thing if you don’t have control of grain size.

The other side of the equation is control over the process. If your tools will not allow you to precisely duplicate the process every time, you really may need to test every single knife to be certain you got what you want. If you are equipped to precisely, and consistently duplicate the same treatment on every blade then you have the very pleasant luxury of taking a sample from a batch of knives and testing that, and can put more faith into single tests such as Rockwell.

I also Rockwell every single blade I make several times in the process. At one time it was not necessary, and before I got other equipment my tester often sat unused and I wondered if it was worth the investment, now I use it so much that I will probably need a new stylus soon and it has totally saved my butt more than once.
 
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