Sharp inside corners and Stress Risers.....

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Cushing H.

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I am still looking at emulating the guard construction technique demonstrated in the Loveless video - and I am still pondering something: Loveless makes no point at all about having a sharp inside corner in the notch he grinds out for his bolster/guard - he just profiles it and sends it out for heat treating. *Yet* - there is this pervasive statement on this forum that one should NOT have a sharp inside corner, because this acts as a stress riser - and can/will lead to fracture at that point during HT.

Question: has anyone actually experienced a crack/failure of a blade, especially during HT, that started at a sharp inside corner?
 
I have never had a blade with this kind of notch fail during heat treatment, or afterwards. I've made about 60 0r 70 blades this way. I always send my knives out for heat treatment.
 
A hidden tang is more susceptible to failure in that area than a full tang like the Loveless would be. But that doesn’t mean it can’t fail, so I choose not take a chance. Best practice and all that…, . Ever seen it? No I haven’t, but.
 
DanF said:
A hidden tang is more susceptible to failure in that area than a full tang like the Loveless would be. But that doesn’t mean it can’t fail, so I choose not take a chance. Best practice and all that…, . Ever seen it? No I haven’t, but.
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I'm wondering if this is one of those things that, in *theory* is correct, but in *practice* is not really a risk......
 
Cushing H. said:
He made no mention in the video of radiusing that spot.....
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It must be in the book, then. He spoke of radiusing it to fit the mill bit with which he cut the slot. The question then becomes whether a 90* cut straight versus radiused around an axis improves strength.
 
fitzo said:
It must be in the book, then. He spoke of radiusing it to fit the mill bit with which he cut the slot. The question then becomes whether a 90* cut straight versus radiused around an axis improves strength.
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so. .... this is the non-machinist in me coming out - are endmills available with a know radiused corner? If so, one could use such an endmill with little concern about too "sharp" a 90 degree inside corner at that point.....
 
Yes, radiused endmills are a thing, definitely. Get a .02 radius mill and it's enough. Loveless, however, radiused the inner face of the slot. I apologize, I am having a hard time explaining it. Hopefully someone comes along with the correct terms and clarify this.

Nonetheless, the radius endmills would solve that problem and a couple swipes with a file on the guard would fit the radius. Not a bad fix at all.
 
I don't know if I'm allowed to post this or not, but a thread on another forum shows the closest what I mean by radiusing the slot. First notice the guard and how it's been milled. Then considering hand filing the radius in that slot to fit that guard (the fellow did the entire tang section in this case, no slot), using a radius gauge to get the arc correct.
I concluded that he had much better precision control of thickness in his process, ie, he had his stock machined to a very specific thickness and finished so he could match it accurately with a 3/16" mill to slot the guard. From what I remember, though, somehow the physics of that arc despite the 90* to the cut greatly reduced risk of stress risers.
 
fitzo said:
I don't know if I'm allowed to post this or not, but a thread on another forum shows the closest what I mean by radiusing the slot. First notice the guard and how it's been milled. Then considering hand filing the radius in that slot to fit that guard (the fellow did the entire tang section in this case, no slot), using a radius gauge to get the arc correct.
I concluded that he had much better precision control of thickness in his process, ie, he had his stock machined to a very specific thickness and finished so he could match it accurately with a 3/16" mill to slot the guard. From what I remember, though, somehow the physics of that arc despite the 90* to the cut greatly reduced risk of stress risers.
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Ah ... I see. That would NOT be easy....
 
DanF said:
View attachment 1737099
Page 127, HOW TO MAKE KNIVES, Barney/Loveless
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I was kind of wondering if that approach would work. the slot would then not keep the guard in the correct vertical position .... I guess you need to correctly position the thing to get the right angle, then rely on the pins to hold position.... ???
 
Cushing H. said:
Ah ... I see. That would NOT be easy....
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I agree, definitely NOT easy. It is a practice-acquired skill but is not as scary as it seems with a good pillar file or two and a radius gauge.

I got it down pat when I made 40 Loveless style drop points in a row. That was back around '88 and it was the end of me ever making that particular knife pattern again. Burned me out and was the beginning of the end for me selling knives.

It does, however, address the stress riser issue, so I thought I'd mention it.
Good luck with, and have fun with your project.
 
fitzo said:
I agree, definitely NOT easy. It is a practice-acquired skill but is not as scary as it seems with a good pillar file or two and a radius gauge.

I got it down pat when I made 40 Loveless style drop points in a row. That was back around '88 and it was the end of me ever making that particular knife pattern again. Burned me out and was the beginning of the end for me selling knives.

It does, however, address the stress riser issue, so I thought I'd mention it.
Good luck with, and have fun with your project.
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thank you Mike!
 
i guess you have to decide if you are going to take the advice of people on the forum, or bob loveless. :) i have been doing mostly loveless inspired knives for years, all with the slotted /pinned/soldered guard. i have never had it happen. i have used both high carbon and stainless. as far as a radius slot, the guard slot and ricasso on a drop point hunter is rounded on the guard side, and one side the chute knife is rounded as well. i dont think that helps or hinders the stress riser area. do you have his book or the video? the video is the way to go. actually watch both videos, jim merritt gives some great tips as well. robert loveless an american legend, and the loveless legend. they might even be on youtube by now. i thought the video showed him rounding the ricasso with a file, i could be wrong, its been a few years since i watched it. post #10 in this thread shows page 127 from the loveless book, but thats not bob's, thats michael collins and his blade. when you mill a guard slot it automatically leaves a rounded stopping point, you do not need a particular tip. you just round the ricasso until it fits. i put a file guide around the tang so my file never touches that guard tongue while rounding the ricasso. the loveless utility does not have any rounding. there are plenty of loveless style knives in the gallery on my website link below if you want to look.
 
The one thing not being mentioned is the amount of "Finish" in the notch. If you don't take the time to remove deep scratches with files and sanding you're leaving the area open to stress risers. The same reason you do a finer sanding on the "Spine" to eliminate deep scratches before heat treat. This holds true for 90 degree or radius corners, stress risers develop in those deep scratches. I've made several hundred of these, never experienced a failure.
 
In Loveless they make lot of knife , it is some kind of production .They must keep production as simple as they can .Slot in guard is milled and they leave that half round end because to make it square need lot more additional work , probably hand work because I don't know which machine could do that .And that is the part that must remain precise for good fitting , one wrong move with file and you are done .Rounding on ricasso is more simple/ forgiving and faster step then to square guard slot .
One more thing .....Guard and ricasso don t need to fit prefect in that place , it is only necessary for the guard to go deep enough into the ricasso, even if they do not have full contact , from the outside nothing will be visible .
 
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