broke tip off knife

wrencheshurt · Apr 10, 2012

Hey guys, I don't post much I'm more of a lurker, I read and absorb as much knowledge as i can. I am working on this drop point hunter I just made, it is made of Aldo's 1084 it is 3/16 thick 4.5 inch blade and 5 inch handle. I heated it to non-magnetic, quenched in warm canola oil and tempered 2 times at 2 hours each at 450f. I was grinding the edge down after heat treat dipping in water every pass and got the idea to put an edge on it and cut some wood up and check for warps, bends and chips. I stabbed the 2x4 and broke the tip off twice. I cant figure out where this went wrong, i know the heat treat is rudimentary but we all gotta start somewhere. heres the pics hope it works:

sorry for the crappy pics all i have is a camera phone.

thegeek574 · Apr 11, 2012

I can't comment on the HT, though, if I could, seems to be just about right, but I would say that the grind looks really high, meaning the there is a good chance that the tip is pretty thin. keeping this in mind, I have broken tips off for knives with thin tips prying wood, and so I would think your would suffer less from a bad HT and more from a incorrect use of the knife based on it's edge geometry. However, feel free to correct me becuase this is coming off a sleep deprived, schoolwork addled mind, so I might be completely wrong.

fast14riot · Apr 11, 2012

What grit did you stop sanding at before HT? 3/16" even with a FFG should be able to hold up to stabbing and drilling, but prying with the very tip will likely result in a shorter knife. I say split the difference and bing the spine down halfway and the edge up. Not the end of the world, bigger upsets are bound to happen, the first time I had a blade crack in quench just about made me want to quit!

-Xander

Patrickknives · Apr 11, 2012

Seems like everything should have worked out better, I would like to see a different view to see how thin the tip is. If it is really brittle you should redo the temper , maybe check your oven temp with a different thermometer

A C Richards · Apr 11, 2012

If you are twisting out after stabbing the tip is probably too thin. If it is snapping off from stabbing then it is way too brittle. It could have been overheated slightly as it does not seem you have a really accurate means to tell temps when heat treating. What did the cross section look like? You can try to raise the tempering to 475f. If it is still too brittle bump it up another 25 degrees until the desired hardness/toughness ratio is achieved. But from what you described the HT should be fine so you can play or live with it, your choice.

mete · Apr 11, 2012

Did you use a torch to HT ?? If so it's VERY easy to overheat the tip => causing large grain size and very brittle.
It's also VERY easy to overheat the tip when grinding !

Bailey Knives · Apr 11, 2012

I use a forge and pyrometer for heat treat, and still I get an overheated tip at times. I usually jab the tip into a 2x4 and intentionally snap the tip off if I feel it is too thin. Then I slightly reprofile the knife and grind the bevels a bit and the new tip is much stronger than the old one. I am not saying this is the best or even the right way to do it, but if I were you I would reprofile it a bit and call it good.

Carl_First_Timer · Apr 11, 2012

The tip looks to me like it was a bit thin. Again it could be my perception of the picture, but it looks like you convexed the entire blade, and had no spin to strengthen the tip.

Bailey Knives said:
I usually jab the tip into a 2x4 and intentionally snap the tip off if I feel it is too thin.

I'll have to remember that one.

wrencheshurt · Apr 11, 2012

I sanded it too 400grit before heat treat. I didn't use a torch, I used my A/C bottle forge with a venturi burner lined with kaowool. I didn't bend the tip when stabbing but I did stab pretty hard. I went and purchased an oven thermometer and the oven is accurate. I did a third temper but im just gonna leave this one be and start on another one, thank you for the replies.