How do you test your ht?

O

Omega Leather Works

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Jun 13, 2007
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Hey guys.

I'm getting ready to ht some 1084 and it occurred to me that I don't really have a testing procedure in place.

I'll probably start with a cut off stamp to verify that my procedure yields hardness with a file, but then...?

Obviously (since I'm using a file) I don't have a hardness tester, so what things do you do to test for correctly tempered blades?
 
aarongb said:
Take it with a grain of salt, but I got some of these http://www.amazon.com/Flexbar-Hardness-Testing-File-Set/dp/B001CTI7TE . I didn't get them from Amazon, and I remembered them only being around $60. I like to think they give me a pretty good guess at the range, based on testing on knives with a known HT.
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Thanks man.

Are there any procedural things you do in addition to testing with the files? What I mean is cut tests, flex tests, breaking to look at grain structure, etc...?

If so, how do you do them?

Btw, I don't mean every knife you guys make. I mean testing to verify/improve your heat treat. I hear a lot about how testing is important, but have never seen it mentioned HOW you're doing that testing.
 
Test the knife by doing things the knife is meant to do. Hack through a few 2x4's or branches with a chopper and use a kitchen knife in the kitchen for a while to see how well the edge holds. These will show you if the edge is hard enough or tough enough.
 
After quench, check the edge with a good file. It should skate like it was on glass.
After temper, check again. It may bite a tiny bit, but should mainly skate along the edge.

After grinding a preliminary edge, examine the edge closely with a magnifier, and then place the edge on a 1/4" brass rod ( lay the rod on the table) and flex the blade to the side. You don't need to flex it very far, just enough to clearly see it deflect. If you look closely ( optivisor hood is good here), you will see the very edge flex a tad to the side. If the edge is ground thin, it won't take a lot of pressure. If the blade has a thicker edge, it may take more side force. I flex left then right. Remove the blade and inspect the edge with a magnifier.

1) The edge flexed back nearly to center and looks just like it did before the test - The HT was perfect and temper was at the right temperature.
2) The edge flexed back a little, but stays bent to at least half the amount of flex - The HT was either not quite sufficient, or the temper was too high. If it is very minor, I would continue with finishing the blade and put a slightly thicker final edge on when sharpening. If it is more severe, re-do the HT and temper at a lower temperature.
3) The edge rolls over and stays bent - Probably a poor HT - Re-do it.
4) The edge chips out - Temper is too low. Temper one time at 25F higher and re-sharpen the blade. Test again. If it still chips, temper another time at 25F more.

Next - Cut some stuff up. Cut rope, heavy cardboard, while up a 2X4 and chop on it. If it is a kitchen knife, cut the rope and cardboard and then cut some veggies. These cutting tests should tell you how the knife performs. After the tests, examine the edge with a magnifier and look for tiny chips or a rolled edge. Chips indicate the temper was too low, and rolling indicates it was either a poor HT or the temper was too high ( it is almost always the HT, not the temper).
 
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I got a set of hardness files and use them as a base reference. I have blades that I had tested that I can use for comparison. The files really only tell you if you are in a range, but if your heat treat was bad they will tell you right off that the heat treat was not optimal. Past that I will do cut testing with a blade.
 
Strigamort said:
Thanks man.

Are there any procedural things you do in addition to testing with the files? What I mean is cut tests, flex tests, breaking to look at grain structure, etc...?

If so, how do you do them?

Btw, I don't mean every knife you guys make. I mean testing to verify/improve your heat treat. I hear a lot about how testing is important, but have never seen it mentioned HOW you're doing that testing.
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Bear in mind too, depending on your HT atmosphere you will have a layer of decarbed steel. So be sure to scrape that off 1st before you use the test files.
 
Thanks Stacy, I know that I used to know that, but I've since forgot. :D I believe it was in (at least) one of my books on the topic.

I'm surprised that no one has declared their exact testing procedures, but there could be any number of reasons for that.

People that obsessively test their sharpening practices probably have more time to invest as it's typically a hobby devoted to just that.

I can figure out what angles are appropriate for 1084 based on an example of something I heat treat cutting various media. This, of course, ties in with the recommendations that I've already received in this thread.

I was just curious about how you all determine a successful hardening given the steel(s) you use. :)
 
As soon as I get through the quench I take a file over it to see if it skates. If it does it's good and then on to tempering. after tempering I sharpen it and do a few things. I do a brass rod test and hit the spine with a rubber mallet to see if it cuts. If it does chip or dull to easily I know its good. Sometimes I take the knife to 2x4 to chop through it to see if the edge holds up. Ocasionally I make a sacrificial lamb type blade and do some extreme testing. I hammer it into my bench vise and then bend it in the vise to see how far it will bend.
 
beaster456 said:
As soon as I get through the quench I take a file over it to see if it skates. If it does it's good and then on to tempering. after tempering I sharpen it and do a few things. I do a brass rod test and hit the spine with a rubber mallet to see if it cuts. If it does chip or dull to easily I know its good. Sometimes I take the knife to 2x4 to chop through it to see if the edge holds up. Ocasionally I make a sacrificial lamb type blade and do some extreme testing. I hammer it into my bench vise and then bend it in the vise to see how far it will bend.
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Interesting. I can't see chopping with the tiny little knives I've been making, but snapping a blade seems to be in order.
 
A file, or pricy sets of "testing files", will tell you almost exactly nothing - or more to the point, they will tell you what you think you want to know. The margin of operator error is so great that I consider them completely useless.
(I can lean into a 64Rc blade and make a deep scratch with a 60Rc file... or use a light touch and "skate" that same file across a piece of annealed steel... so what?)

A professional facility with a properly-calibrated Rockwell tester will get you in the ballpark of what you want to know - overall average hardness in the martensite matrix.
(this still only tells part of the real hardness of the blade... it cannot reliably tell us about carbide content and other important factors)

Brass rod "tests" and the like will tell you a lot more about how thin your edge is, than whether or not the whole blade is tempered properly.
(false readings can be achieved remarkably easily)

Clamping a blade in a vise and pulling on it tells us almost nothing at all about hardness or toughness, except whether it stays bent or springs back or breaks at a certain point... flexibility is almost entirely dependent on geometry, and whether or not a blade snaps off under lateral pressure has very little to do with how well it will resist dulling or breakage when using it to cut/slice/chop stuff.

Ever seen an ABS journeyman or mastersmith test with a thick bowie? Of course, that's a huge part of our culture as modern knifemakers.

Ever seen the same tests done with a light, thin kitchen knife made a journeyman or mastersmith? Guess what? The thin blades generally perform better overall.

Breaking a blade on purpose is interesting, but not really very instructive, unless it's done under very controlled circumstances.
(only the worst "grain" structures will show up to the naked eye)

jawilder said:
Test the knife by doing things the knife is meant to do.
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Yes! That's really all that matters.
 
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I use my hardness tester to see what hardness I am at and because I am curious. After HT I clean the decarb off and test to see if I hit close to the max HRC for that steel. If I get say 66-67 for 52100 vise 55 then I know I did something right. Then temper to close to the desired hardness. Sharpen and do the cutting test. I usually cut some cardboard, thin paper, some wood, then hit up some antler. This is for my average knife, not for say a kitchen knife, that is more using like Stacy said cutting some veggies and what not.

I have broken blades before and have noticed very easily with a optivisor differences in grain structure. Not obviously like Kevin Cashens microscope but good enough to know if I am doing something good or bad for that particular steel. This isnt something I do all the time, usually when I have new steel that I have not played with before.

All of these things thrown together can give ya an idea of how things are going with your blade IMHO.

James kind of curious why you dont agree with using a hardness tester to find a rough HRC for a blade that isnt in a professional facility? If I have a calibrated test block that is in line with what I am shooting for and it accurately reads that why wouldnt it accurately read a piece of steel as well as long as you take into consideration cleaning and smooth surfaces and all that stuff for accuracy?
 
quint said:
James kind of curious why you dont agree with using a hardness tester to find a rough HRC for a blade that isnt in a professional facility?
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First of all, there's no point to finding a "rough" Rc. Those values are not linear in scale, and a difference of one or two points can represent a very large variance. For instance, when you see a company or maker (and there are many) who advertise an Rc value of 56-59RC... that means almost less than nothing... it only proves that they don't really know or care.

Perhaps I misspoke or was misleading... I do indeed use Rockwell readings as a baseline (actually, the firm that does my HT for me takes 2-4 Rockwell readings per blade and averages them out, to help me establish that baseline). If you are carefully and accurately calibrating your Rockwell tester, I would certainly include that as a "professional facility"... however, and no offense meant, I don't know you and frankly I have no idea what cal blocks you're using, or if you know how to use them properly, or... etc etc. So I don't trust your readings.

I do trust the folks who do my HT and Rc test my blades, because A) they're a widely respected company, and B) as far as I can tell they've been extremely consistent over a period of several years.

My point is, even the most accurate Rc reading is only a starting point, and while it's probably the most reliable of all the testing methods we've discussed, it still only tells part of the story.

Keeping the materials and HT process repeatable and under control is obviously hugely important. Those other tests are not repeatable or easy to control, so I have zero faith in them.

The proof's in the pudding. The knife either performs as needed or it doesn't. That's my final test.
 
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Ok gotcha ya. When I say "rough" I was just hinting at the fact that its not going to be a exact number per say (close average). Like you said (and one of the first things I learned) is to take several readings and average them together. Thanks.

Agree, walk the walk.
 
I've got those cheap Chinese hrc files.
NOT RECOMMENDED for a any knifemaker.
Every set i've touched had at least one file with wrong hardness.

But I am not a knifemaker, but an enthusiast.
And although files won't show that HT is good, they can show when HT is completely off.
Like when O1 or 1095 steel is easily marked by 55hrc file.
 
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