Stress riser failures in blades made from files

[Rich Hale]

This comes up now and then and I have a question for the makers: Has anyone made a blade from a file, left teeth on and had a failure of that blade that started at one or more of the teeth?
I think I have a working knowledge of stress risers and the results of not tending to them. I have not seen one failure from teeth left on a blade. But there is such a large group of makers on here i would like to know about the experiences of others. Let us know if you have had one of your blades fail. If you have a pic of that blades showing the point of failure it would add alot to this Discussion.
Thanks in advance.

[jmccustomknives]

It is very common in files for stress risers to form, forging before grinding the teeth will make cold shuts that will alway cause a failure if in the hardening zone. I have always made it a practice to grind the teeth off, I might leave a hint in the ricasso for the customer to see. I honestly don't think in a stock removal blade that the teeth will cause a stress riser just due to the fact they didn't when the file was made, it's when they are forged into the steel that it becomes a problem.

[ThomasPowers]

Actually even a scratch on the blade is a stress riser; it's just that most blades are not stressed to failure---particularly custom made ones.

(in one of my MatSci classes we studied a heavy walled pressure vessel that failed due to a tooling mark causing a stress riser---a 20 pound chunk embedded itself in a concrete wall next to our professor's head---he didn't mention what grade he gave that Grad Student...)

[Rich Hale]

Thanks for the replies,,Like I noted, I am familiar with stress risers. I was asking if anyone had seen a failure in a knife from file teeth being left on the sides of the blade..For me I have not and have forged file into knives and did not grind the teeth off. I think the key is that the stress needed to create a failure is not reached. Thanks for that key Thomas.

[ThomasPowers]

Personally I try NOT to make knives for folks that want to use them as crowbars----I send them to Cold Steel and I figure we all 3 end up happier.

[jmccustomknives]

I prefer to over build my knives. I use mine for crow bars. I've never had one fail due to a stress riser, that being said I've always tried not to leave anything that would cause one. It might be fun to take one of my old files and forge it out and see what it takes to make a stress failure. If I get a failure I will post a pic.

[metal99]

Just a thought but what if you only edge quenched or drew the temper from the spine? That would probably help a lot maybe?

[Woody]

35 years ago when I first started forging blades, I decided to make a knife out of an old file. This was long before anyone ever mentioned such technical terms as annealing to me. I heated it to a bright orange or so and hit it with my hammer. The thing shattered and red hot shrapnel went everywhere. This was also long before I had any sort of protective clothing like a leather apron. I nearly set fire to the family tree. That was my first, last and only experience with files as blade material. Not at times I mentor the kids in the Blacksmith Club at the School of Mines. Someone gave them a bunch of old files and they beat them at anywhere from dull red to almost bubbly yellow with no ill effects that I have seen. Me, I am still a little nervous around them though.

[jmccustomknives]

Woody, that first file sounds like you over heated the steel. I've had that happen a few times when I wasn't paying attention. I do edge quench, and I think that's the key . Not the edge quench but not having anything that could cause a riser when you get to that point. I've got a video showing a guy quenching a blade before he did any grinding, I believe this is a sure fire method for this kind of failure. I'm going to run the experiment tonite forging a file, I will use this method. I think I can get a stress failure.

[jmccustomknives]

Ok, I hope the pics come through. I forged a small dagger from a half round file without removing the teeth. The knife was tempered @400F cleaned up a little and then tested. I dropped it on its point without failure. Then I put it in the vice and flexed it. It broke rather easily. If the pics don't come through I'll try to describe the outcom. On side (I think the flat) the grain was clean, on the half round side it was choppy and course. You'll notice a couple of inclusions from sunk in teeth, they were not visible from the outside. Forging with the teeth may work if you grind out the inclusions before heat treating, but I'd rather do it first than take the chance of a falure. Like my attempt at posting the pics if they didn't work. 0

[metal99]

I copied the links and the ones that worked were really small. When you highlight over the pictures on photo bucket are you choosing the bottom link to paste? I think it gives you 3 or 4 to choose from, the one at the bottom is the one you want.

[jmccustomknives]

[Fatboy Rider]

thanks for the experiment. and the interesting topic