The "Ask Nathan a question" thread

Great stuff, as always.

How do you know so much about this stuff? Did you take classes? Read books? Just from needing to know and self studying?

Really curious where all this came from that got stuffed in to your big brain.



Nathan the Machinist said:
The secondary hardening hump is seen in many complex steels where the hardness plateaus and then rises with tempering temperature where you may see a higher hardness at 950 F than you see at 850F for example. The cause is two fold: one is the conversion of soft retained austenite into martensite (the hard structure of steel) and the other is the precipitation of secondary carbides which can increase the hardness of the structure through dislocations and also increase the measured hardness simply by reducing the depth of the dent from the diamond during the test. This is all well and good if you're a commercial heat treater simply trying to hit a particular hardness number on a tool without messing it up and can be necessary on tools subjected to certain coating and processes that exceed a lower temperature temper.

It's a bad idea on knives.

There are other ways to address retained austenite that are better for a knife application and tempers above a certain point allow the matrix to relax around any eta carbides formed from cryo, negating their pinning effect.

So when the dude a chump pump points a finger like a stump
Tell him "step off, I'm doin' the Hump"
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xxwarderxx said:
Great stuff, as always.

How do you know so much about this stuff? Did you take classes? Read books? Just from needing to know and self studying?

Really curious where all this came from that got stuffed in to your big brain.
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constant updates from the mothership, is my guess
 
Matthew Gregory said:
I could be The Walrus.

...wouldn’t that also make me The Eggman?
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You're not the Walrus. You're not the Eggman. You might be a Space Cowboy. Some people call you Maurice but I think that's because they're uncomfortable with your status as The Gangster of Love.
 
xxwarderxx said:
Great stuff, as always.

How do you know so much about this stuff? Did you take classes? Read books? Just from needing to know and self studying?

Really curious where all this came from that got stuffed in to your big brain.
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I attempted my first heat treat in the woodstove when I was about 12-14. I'd made a few shitty knives before I went to school and in addition to a really basic education glossing over basic metallurgy concepts in some materials and processes classes I cornered a knowledgeable processor to learn more about the subject. NCSU has a really good library, a big part of the 5th floor had a enough information on metallurgy it would take a lifetime to absorb it all. Which I totally didn't. So I've had a lifelong interest in the subject and some very basic formal education but no real in-depth knowledge. It was some on-line discussions with Cliff Stamp almost 20 years ago that got me started down the path of the low temp tweaks. Before then I was of the (incorrect) opinion that you should just follow the instructions as if you were baking brownies. I would butt heads with folks on this forum who were just so damn certain that you should only follow the recommendation in the data sheet because there is no way they could possibly have missed something. When the current literature finally did substantiate what I was talking about with low temp D2 folks began to more widely adopt my heat treat for that alloy and it became mainstream. All of that started with Cliff Stamp. He's not a metallurgist either and I don't think he's done a lot of real world applied heat treat development but that's where the underlying concept came from. Unrelated but a fellow in Germany named Roman, who is a metallurgist and does do real world applied heat treat development, was also going down a parallel path and many of the concepts that we use for the 3V low temp tweaks are similar to what he does, with a few differences.

The optimized HT for D2 and 3V were developed through an iterative process not unlike evolution. While an in-depth background in metallurgy would certainly be helpful for anyone attempting to optimize a HT, the reality is I am not a metallurgist nor a subject matter expert. I simply utilized a technique not unlike that used in any industry to optimize a process. A laboratory grade heat treat setup and specimen production techniques helped improve the signal to noise ratio and some real world experience and perspective helped setup meaningful and repeatable cut tests. The end result worked out pretty well.

The best book on the subject that I have read is Tool Steels 4th and 5th edition and of course Verhoeven. But even discussion in the most current literature leaves out a lot of important factors so reading the information there and applying what you see in things like the RA tables or pre-quenching doesn't always apply perfectly because things like quench depth and quench speed and vanadium content of the samples isn't even discussed and it matters. I think a lot of the best work out there isn't published. The one thing I do know is the literature keeps changing, and that right there tells you something. I know a couple of metallurgists and the one I respect the most is also pretty old and has seen enough change over time to have developed an open mind.


edit to add: I hate to say it, but you learn a lot by doing it. While there is no substitute for a real education, even the smartest most educated folks are sometimes wrong in the worst kinds of ways because they lack real experience and real perspective to develop the ability to even see they're missing something. Beware the internet experts who have never actually set up real cut tests and performed the heat treats and evaluated the actual outcomes. These folks can be an excellent source of general information but sometimes they'll come to a conclusion, and feel 100% certain about it, and sometimes they can be wrong. There is a very common human failing to believe everything they've read in a book that makes them an expert. Book knowledge is very important but actually doing the work and making meaningful measurements and forming meaningful judgments is also very important to developing a complete understanding of a subject. Or put another way: if you believe wear resistance = edge retention because something you read and you haven't actual cut stuff, you're missing part of the picture.
 
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Hi Nathan, has there been a slight change in the MashedCat sheaths for the production MC pattern? In other words, was a new blank sent to Eric to commission the sheaths for the production MC as opposed to the 2018 "proto" MCs? TIA.

NMV, sending Jo an email for her or your attention :)
 
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Casinostocks said:
Hi Nathan, has there been a slight change in the MashedCat sheaths for the production MC pattern? In other words, was a new blank sent to Eric to commission the sheaths for the production MC as opposed to the 2018 "proto" MCs? TIA.

NMV, sending Jo an email for her or your attention :)
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Hey Guys!

It looks like in my excitement to get these moving, what I thought was MC sheaths was actually BC sheaths and there have been 6 sent out wrong. I will be in touch with you 6 and we will get it fixed. My apologies! Thank you Mat!
 
Jo the Machinist said:
Hey Guys!

It looks like in my excitement to get these moving, what I thought was MC sheaths was actually BC sheaths and there have been 6 sent out wrong. I will be in touch with you 6 and we will get it fixed. My apologies! Thank you Mat!
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Hopefully maybe it was just mine that was mixed up due to sheath misplacement but if not too many preorders have been fulfilled so far and with only 10 x MCs from Friday before last, the mixup should be less painful :(

By an large most folks read the sub and the way to tell is first of all, the sheath may drop to their ankles (if they're pint-sized like JoJo :p :D) or else there'll be a bit of a rattle / wiggle toward the tip area but if you never had a BC before you probably will not be able to tell the differences because the forward lanyard hole and everything else lines up tight and snugly. If none of these tell-tale signs exist, you most likely have th correct sheath :thumbsup:

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There is a misconception that full flat is "slicer" than saber, and while there can be correlation, that view is missing an important dimension.

The cutting characteristics are based on the edge geometry, thickness at the edge and the primary grind angles. That's what sees the work being cut. There is a sweet spot for those primary grind angles, very specific numbers I use for specific applications. Forcing those grinds to become full flat without narrowing those angles would involve thickening the spine or shortening blade width. There are compelling reasons to do those things some times, but there are plenty of alternative design choices one can make to achieve the same goals of cutting properties, weight and strength.

Ultimately I don't think one way is inherently better than another but you will see many knives that are Berger ground taken to full flat because it is difficult to achieve straight and even grind lines on a saber grind using that manufacturing process and you will see knives that are CNC milled made more as saber because you get better opportunities to fixture certain cuts that way. Either process can work either way, but one does tend to gravitate towards pieces that are a better fit for the process. Some hand makers like full flat because it's easier to prevent screw ups along the spine and wandering lines, some like saber because they're good at grinding them (unlike a Berger, people can feel and see while grinding) and it may work better with their process. There are decisions made based upon a person's preferred way of making a knife that actually has nothing to do with the properties of the knife. That's fine if it isn't a compromise on the performance of the finished work, and depending on the design choices made it frequently isn't.

Do you paint a wall up and down or side to side. Depends on if you're using a roller or a sprayer.

Here is an example of the design process where one is making these decisions: Take our Comp Chopper for example, it is essentially a full flat. One disadvantage to a full height grind in that application is a tendency to stick when fully buried in a cut so there is relief ground behind the shoulder to reduce binding due to the more obtuse angle between the planes. By going to thinner stock but keeping the grind geometry unchanged it will become a saber grind. The thinner stock will reduce weight slightly but I can put it right back by changing the relief cut. So that exact same functional design could be full flat or saber, depending on the shoulder width. And I'm considering doing this if I ever make them again so I won't have to manually blend and round the shoulder transition (a tweak we made to reduce sticking).

TLDR: either approach can make equivalent designs. We tend to gravitate towards work we're well suited to.
 
M390 and other steels with similar properties seem to be the go-to steel for premium folders.

What’s your thoughts on these steels compared to the Elmax, D2, and AEBL currently seen on CPK blades and does it have any place in a future CPK offering?

I’m also curious how much more performance you could get out of them than the current heat treats offer.
 
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