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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #1  
Old 03-09-2017, 02:42 PM
irishknifeworks irishknifeworks is offline
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Hardness Tester

So I'm reaching a point where I really need to know where I'm at. Yes, I know you can tell if you're getting a hardened blade after HT. But I want to go to a higher level than that. So my question is "Do I really need to invest in a hardness tester"? Do you guys have one? If it's that important I'm willing to spend the money (I hear they're expensive). I sell a knife here and there and I'd like to be able to tell a customer what he's getting. I also want to know if I'm consistently turning out properly heat treated blades. So what do you guys think? Is a tester the way I have to go? If so, what recommendations do you have on what I should get?
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Old 03-09-2017, 03:35 PM
jimmontg jimmontg is offline
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Scratcher files?

Well if you wanted a set of scratcher files like I have they are cheaper, but I made mine when I worked in a machine shop. They tell me if I'm close as I have a 60 hard and 57, 58.6 and 62 and 55, 54, the 54 is an old gerber knife, pathetic. You do not want a set that comes in 5s 45-50-55-60- as 59 is 10x softer than 60. But it does tell me if my knives are too hard and also too soft. 58 is my minimum for selling unless I have a reason for a softer more flexible blade. Like a big dagger I don't want to be hard as it's for fighting and not so much cutting hopefully. Blade needs to flex if it hits the rib bone of a bear. Seriously, I made one for my son, told him a bigger gun would be better.

Maybe some guys could make you a set.
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Old 03-09-2017, 04:03 PM
irishknifeworks irishknifeworks is offline
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I'm not sure I trust my judgment when it comes to using scratch files. I use to use the old "does a file skate across the blade" test. I was never really sure whether it did or not. And then there are always different degrees of how well the file skates. So I'm not all that confident in using test files (Not the file's fault, it's just my judgment). I'd like to have a more accurate measure of hardness. Am I being too anal about the whole thing?
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Old 03-09-2017, 07:00 PM
Doug Lester Doug Lester is offline
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I would say that most makers don't have a Rockwell hardness tester. You have to have the right conditions to set one up. Like fairly constant temperature and humidity and a clean environment. Something that I don't have. There is also a curve in learning how to use one and also learning their limits. One problem is with shallow hardening steels like 1075. You have to measure parallel surfaces which pretty much means the ricasso. A shallow hardening steel may not have a hardened ricasso due to the thickness or at least it may have mixed phases. That will tell you nothing about the edge of the blade which you can't test accurately due to the fact that the surfaces are not parallel. The way around that is to forge of grind out a coupon less than 1/8" thick with parallel surfaces and test it and hope that the edge of the blade came out the same way.

With all that most of us just use some sort of a performance test like driving the edge through bailing wire or a thin brass rod. You can also test your heat treating method by making a test knife and working the heck out of it and maybe even testing to destruction.

Doug


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Old 03-10-2017, 01:16 AM
jimmontg jimmontg is offline
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Like Lester said, most makers don't have a hardness tester, most don't have scratchers like I do either. It isn't a matter of judgement btw. If my 57 scratcher doesn't scratch it it is harder than 57. If my 58.6 doesn't, but 60 does I know what part of the ballpark I'm in. Close to 59-60 and I can be confident what I tell my customer. 60 is where I like to make my knives, 59-61. These are not files really, but scratching points.
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  #6  
Old 03-10-2017, 08:17 AM
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SVanderkolff SVanderkolff is offline
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Actually I recommend a tester. You can find the hand hed variety on ebay just make sure you get the diamond penetrator, which works well. I used one for years then traded up to the bench top Wilson brand. If you keep your eyes open on theused market, Ours is KIJIJI yours may be Craigslist you can find them occassionally fairly reasonable. It certainly helps withthe peace of mind when I know what the hardness of my steel is.
Steve


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Old 03-10-2017, 10:38 AM
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cnccutter cnccutter is offline
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I too am a proponent of a tester. I feel it is imperative that we test our blades on a regular basis to make sure the heat treat schedule we are using is really giving us what we think. It's great to get a recipient from a friend and think we should be at a Rockwell 59 but unless we test we don't really know. Testing in general is lacking from new blade smiths, I know I was there too. 😀 I now test on a regularally with both test files and a counter top Rockwell tester just to make sure I'll still where I need to be.

Start with files if that's all you can afford at first, they are better than nothing. I've seen two Rockwell testers on crags list in the past few months go for under 300, so just start watching.

Erik
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Old 03-10-2017, 01:15 PM
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Andrew Garrett Andrew Garrett is offline
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I have a Rams Rockford bench-top Rockwell tester, but for the reasons alluded to earlier (parallel surfaces) I find it hard to test most of my knives--especially since I do mostly clay quenching which means the ricasso is no good for testing anyway.
Typically, it is only used on stainless blades coming out of the Paragon which are homogenously HTd.
I file test most of my carbon knives and that's about as good as I can get with any regularity.

Tip: Before file testing, be sure to wipe, scrape, and even sand away any black gunk at the testing point. You want clean and bare steel only. The file will bite the gunk on top of hard steel and make you think its soft.

Another tip: Before using a bench top tester, be sure to finish the surface to be tested to 400 or even 600 grit. Coarser grits will give softer readings as the penetrator presses down into a rough grit scratch line.

I could probably be talked out of my hardness tester--for the right price.


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Old 03-10-2017, 01:52 PM
jdale jdale is offline
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I am so glad I bought my Rockwell hardness testers, and yes I said testers. I was able to get two from a closing heat treating shop for under $400 TOTAL.

I tend to be a perfectionist spending too much time obsessing on the smallest details. That being said, Not knowing if i have been getting the most from my blades bothered me more than I can possibly express.

All of my testing have proven my processes were sound, but the fact that I now have physical evidence of that has made a huge difference in my confidence level as a maker.

They are not absolutely necessary as there are other tests to verify hardness, but they are so very nice to have.
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Old 03-10-2017, 04:38 PM
jimmontg jimmontg is offline
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Irish it is also a matter of how many knives are you going to make? I at most may make 8-10 in a month, (sent a batch to Peters HT recently, high amount for me), but typically I'm a hobbyist so if I was to spend $600 for something, it probably wouldn't be a hardness tester. My friend Dtec got a nice tester that Ray Rogers recommended for around $600 I think, ask them. Now, let's say if I were Mr. Garrett I would make some scratchers for my forged and Hamon blades just to get a better idea of how close I was, but Mr. Garrett is a master and has a fair idea already I'm sure.LOL

It's like if you're going to make a lot of knives buying a dewar for liquid nitrogen is a good investment, but they are expensive. This hobby can be kept down to a fairly low price and you can still make very nice knives, but for the best of the best you will spend money, there is just no getting around it past a certain point, but it isn't necessary.

There is also the "I want to make the best possible knife I can and though I won't make a profit I still want to do it" attitude and there isn't anything wrong with that. It's how I feel. Nice to make some money for sure, but on some knives I was just making the best I could and when I sold them I made about $3-4 an hour.

First knives I ever made were like that.
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Old 03-10-2017, 05:55 PM
irishknifeworks irishknifeworks is offline
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Well, I'm thinking I'll get some test files and patiently be on the lookout for a really good deal on a portable tester. My shop is small and I really don't want a benchtop tester.
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Old 03-11-2017, 03:56 PM
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Andrew Garrett Andrew Garrett is offline
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Master?! Ha!

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Old 03-11-2017, 05:17 PM
Doug Lester Doug Lester is offline
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From what I've been told is to watch hardness testers that are being offered on places like Ebay. Both portable and bench mounted. Some of them are being sold because the factory will no longer support them so they will only be good as long as their reading match your test blocks because no one will repair them. Be careful if the add says no returns because that could mean that the unit is only worth parting out. A third thing is to make sue that the hardness tester will measure at thickness as thin as most ricassos get. I was researching some electronic hardness testers that would give Rockwell equivalents and noted that some of them had a minimum thickness of around 1/2" or so. Not much use in knife making.

Doug


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Old 03-13-2017, 12:04 PM
Kevin R. Cashen Kevin R. Cashen is offline
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As a test to tell you if you are making a good knife, the Rockwell test is such a small piece of a very large puzzle that I feel many make too much of it. On the other hand, as a test to help evaluate your heat treatment, the Rockwell tester is an invaluable piece of equipment that you will wonder why you didn?t get one sooner after you start using it. If you are looking get the maximum consistency from a heat treatment that you know is giving you what you want, the Rockwell tester is worth every penny, but it has to be dialed in and used correctly.

What the tester will do is eliminate the human bias and unwanted variables giving you verifiable hard data on your process, but to do this you have to be able to trust that the machine is reading correctly. Do not cut any corners on your test blocks and keep the machine calibrated, otherwise the bad data can be worse that no data at all. Keep the tester in a clean, dry place that has very little temperature fluctuations. Check it regularly with your test blocks and take a series of readings and average them for the most accuracy. I often am shown a single dimple, or one on a coarse finish or bevel, by folks showing they know their blade hardness. I try to smile and keep my mouth shut but they really have nothing as far as usable information.
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