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Ed Caffrey's Workshop Talk to Ed Caffrey ... The Montana Bladesmith! Tips, tricks and more from an ABS Mastersmith.

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  #1  
Old 06-16-2008, 09:04 PM
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To the point

Made a small bird and trout knife 3" blade 1/8 at the spine. Knife had a full distal taper, full flat grind. I was going for thin for delicate work, diff. tempered about 3/8" up a 3/4 inch blade. Anyway was testing the blade (scary sharp) stabbed the blade into a piece of 2X4 about a 1/4" did a twist out and snapped the point. It was fairly thin, point broke back to about a .015 thickness, just wondering if this is normal or did I do something wrong. Oh yea! Blade was 1080, oil quinched @ critical tempered 2 cycles @ 425 deg. 1hr each cycle.
I hate it when a blade breaks!!!!!


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Old 06-16-2008, 10:20 PM
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My first thought is...how thick was the blade when you quenched? I assume this was a stock removal blade?
Sometimes higher carbon steels will harden well beyond the point that is submersed if they are thin. (since the cross section is so thin, the oil will "suck" the heat out of the surrounding material quickly enough to induce hardening) Tempering could be another issue too. I have learned to temper for a minimum of 2 hours for each cycle, because in the past I experienced just what happened to you. When I increased the temper time to 2 hours, the tip of the knife I was testing twisted slightly, but did not break.

Finally if you want a thin tip to bend rather than break with 1080, you'll have to go to a higher tempering temp.


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Old 06-17-2008, 02:45 AM
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It depends on how much force you had to apply for it to break if it is normal or not. If it snapped like glass then its no good, if it bent a bit then snapped you probably just applied more force than it could take but the hardness was ok.

Try sticking it in a nice chunk of hardwood 3/8" depth then slowly bend the blade and see if the tip snaps before bending. If it does you might need a lower rc.

I've found the same thing as Ed with the tempering. With really thin blades I can get away with a 1 1/2 hour temper cycle but a 1 hour one doesn't work with my setup. I run mine for 2 hours to be on the safe side and it seems to work (they bend before snapping, pass the brass rod test, etc) With thick blades I have to increase the time to over 2 hours.

Another thing could be grain growth due to too high of temps during heat treat. How does the grain look in the broken pieces?
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Old 06-17-2008, 06:49 AM
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Thanks guys, It snapped fairly quick, I reshaped and sharpened the blade with a secondary bevel at about .025 before sharpening it seems to hold a lot better no problem digging wood. I'll have to run another test blade at 2 2hr cycles and see if that gets me where I want to be. Also I'll try forging the point and a slight bevel before grinding. Forging the point could help. This thing is just so thin. But again it was an experiment.
On my forged blades usually thicker (alot thicker) I follow Ed's video and have always had great results,( 2 to 3 2hr cycles at 475) on this one I was going for a little harder trying to almost get that scalpel thing going on. Whats that old saying: If it ain't broke Don't fix it!
Thanks much to you both.


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Last edited by ranger1; 06-17-2008 at 07:01 AM.
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Old 06-17-2008, 07:35 AM
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Sometimes for me its......"If it ain't broke....fix it till it is!"


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Old 06-17-2008, 11:33 AM
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Quote:
Originally Posted by Ed Caffrey
Sometimes for me its......"If it ain't broke....fix it till it is!"
It's good to know I'm not the only one with this malady.


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Old 06-17-2008, 05:29 PM
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It seems that I read a post by Kevin Cashen (I think) recently that said, paraphrased: "I tell my students, that if they want to make a blade strong, make it thin." He explained it very well.

For me, it's question of what the knife is designed for. I generally go for better edge retention on smaller, pocket style cutters with tempers of one hour (once or twice for 1095). Bigger stuff stays in for 1.25 - 1.5 hours.

I always have a good idea of what I'm shooting for when I conceive the design and try to manipulate the blade geometry to suit the desired hardness.


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Old 06-17-2008, 05:38 PM
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I tend to overthink things. I wanted the blade harder than normal to help with edge retention. As I said the knife was to be for dressing small birds and fish. If used solely for its intended purpose the knife would have been awsome. This baby would cut. Then I figured the human factor . Those what ifs get ya every time.


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Old 06-17-2008, 09:52 PM
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Yea, mine are a bit thicker and tapered to discourage flexing. That's how I get away with harder edges.

In my experience, people just don't like to sharpen knives. With all those, "Never sharpen it and it will fillet nails for life with a lifetime guarantee!" TV knives out there, it's hard to convince them that a high quality blade will not stay sharp forever. Hence, max edge retention out of my shop (most of the time).


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Old 06-18-2008, 11:54 AM
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I do have a little bird and trout I'll be finishing up this week-end left the point a little thicker feel better about it.
Thank-you guys for the info.


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