Slysz Bowie Blade Broken: FFG+Spydie Hole Fail?

[tvenuto]

Neither B nor I am metallurgy experts, but throughout the discussion we both agreed that there is no simple cause that leads to this.

Found your issue.

[Surfingringo]

I don't know if compromising the heat treat means it would be fragile to break or if it would actually become stronger to resist breaking.

My best guess is that at those temps, you are annealing the blade and making it softer. That's why it won't take an edge after. It's too soft and weak to maintain an apex. I appear to have done it to the first chef knife I made in a couple spots, and now I grind my edges by hand. :o

Though I don't think that's what happened here. And I don't quite understand the surprise either. Every broken blade I've seen that has a hole (Strider, Spyderco, Benchmade) breaks at the hole. It's pretty intuitive. And every one (and I'll presumptuously include this one as well, because I believe it to be the case) has broken for the same reason: user error. I'm not trying to be a Spyderco defender by any means, but I mean, come on, take a step back and look at what is happening here. The guy was modifying a thin piece of steel, thinning it out even more and applying a power tool to it. And how does he know he was applying less than 10 lbs of force? And where was it applied?

He was modifying the blade. Once you've modified it, you can no longer claim a design flaw since it is no longer the original design, which of course was never designed to be modified in the first place. That case is closed. What caused it to break? Well unless it wasn't tempered properly, the only thing I can imagine causing that is the same thing that causes most blades to break: applied force. Basically, the guy made a mistake on this one. He's gotta take the L.

Sorry to charge in here with such conviction, but I'm just a huge fan of parsimony and it seems pretty obvious. I'm sure the more details you are able to give of what he did, the more obvious it will become that he just messed this one up. Clearly he has experience and does some fine work, but accidents happen! It's all good! What's more important is that he didn't get hurt in the process, unless that tape on his finger is a result of this as well.

Yep, I think thats a pretty fair assessment. We will never know, but because I like to guess, I would bet on what I said earlier. If you are applying pressure with a high rpm tool and catch an edge, that is going to essentially act as an impact on a thin, high hardness piece of metal. "PING"...I have hear that sound before. It sucks, but every time I've heard it, it was the result of pilot error.

[Archimedes]

The title of the thread should be changed to; Home Grinding your knife blade may lead to failure. The current title seems a bit misleading.

[jimmyjohnjohn]

That'll learn ya. Or maybe not.

[remnar]

Neither B nor I am metallurgy experts, but throughout the discussion we both agreed that there is no simple cause that leads to this.

Found your issue.

Nailed it! :D

[razorsharp]

I have reground dozens of knives and I have no idea how you could do this even to a reground blade without absolutely laying into the blade laterally. I feel like it could have had a stress fracture that was only really revealed after the grind.

[anagarika]

I have reground dozens of knives and I have no idea how you could do this even to a reground blade without absolutely laying into the blade laterally. I feel like it could have had a stress fracture that was only really revealed after the grind.

Very likely. I think the best is to get the blade back to Spyderco for analysis. It's a rare happenings, that there might be inclusion / micro crack on the part which was protected by original grind (no surface crack) but exposed after thinning.

Lance's theory also possible, something caught, acted as impact hit to the blade and PING.

We won't have conclusion until the blade is analyzed by Spyderco.

[Fancier]

I don't see the advantage to Spyderco in weighing in on this one.
"You modified your knife and now you want us to figure out why it broke?"
I agree that this is a cautionary tale, "Let the modder beware!"

[Blerv]

The thumb hole has been used for about 30 years now. Very few blades have been broken in that way and many are thinner than the Slysz. I assume if the contrary Spyderco might have rethought their trademark as an opening method long ago.

I'm with Jabba. I don't have enough information to make an educated decision on this but it really doesn't matter as I'm not the modder nor the manufacturer. That said, if the knives are strong enough to stand up to a lock breaking machine while I believe while the hole is the "weakest point" other than the tip it doesn't necessarily mean the blade itself is "fragile".

My own meager collection has a number of regrinds including a few from Razorsharp. These too are much thinner than some factory blades and none have given me any problems. My ZDP Stretch is on par with a Centofante3/4 and much thinner for most the blade; it's been used for about 3 years now.

[SpeedHoles]

Resonance frequency made the brown noise happen and that blade took a SHIfT.

[tvenuto]

The dreaded brown note!

[curlyhairedboy]

I have reground dozens of knives and I have no idea how you could do this even to a reground blade without absolutely laying into the blade laterally. I feel like it could have had a stress fracture that was only really revealed after the grind.

yeah, defects can definitely hang out inside the blade volume. it's when they get to the surface that they see the real big stresses and boom goes the propagation.