Choil, spine notches, makers stamps

since we are on choils....is it pronounced "coil" or "chur-oil"?
 
spyken said:
since we are on choils....is it pronounced "coil" or "chur-oil"?
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Neither, it's pronounced ch (as in chore) - oil (as in coil).

Not sure about the stress riser thing, but I would think that plunges would be every bit as likely to cause weakened areas as would any of the other things mentioned.
 
2knife said:
Do these features cause stress risers?

In the book "How to make knives" Bob Loveless says he uses the photo etch to mark his name on his blades, instead of stamping the blades, because stamping the blade could a create stress riser, or weakened area.

Choil notches, and singular spine notches, similar to Fisk's Sendero.. seems like there might also be a trade off in integrity/strength, for cosmetic purposes. Just throwing it out to the wolves, for some discussion.
Thanks,
David
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NO!!!!!!!!!
 
my personal belief and this is not absed on anything other than my own experiences in my shop is that the only time i have seen a problem with the stamp is when you cold stamp the blade rather than hot stamping. but ther e has to be somebody here with more expertise in this area.
 
2knife said:
Do these features cause stress risers?
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Yes - it might not be material if the knife was properly normalized / heat treated, but all things being equal, a sharp notch, choil cut, raised edge, etc, etc, creates more stress points. (Not sure the stamped name is meanigful though.)

What I don't know is whether normalizing or sphereoidizing the steel would remove them 100%.
 
Keith Montgomery said:
Neither, it's pronounced ch (as in chore) - oil (as in coil).

Not sure about the stress riser thing, but I would think that plunges would be every bit as likely to cause weakened areas as would any of the other things mentioned.
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thanks Keith. that's how I pronounced it until I kept hearing a guy saying "coil".
 
Joss said:
Yes - it might not be material if the knife was properly normalized / heat treated, but all things being equal, a sharp notch, choil cut, raised edge, etc, etc, creates more stress points. (Not sure the stamped name is meanigful though.)

What I don't know is whether normalizing or sphereoidizing the steel would remove them 100%.
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No heat treatment will remove a stress riser. A stress riser is simply a concentration of stresses (and likewise strain when loaded) in a material due to it's geometry. The greater the radius of a corner, the smaller the increase in stress.

A sharp choil is a stress riser, and can multiply the stresses at that point by many times what the stress would be in the bulk blade material, but is it honestly a problem? Even the poorest quality steel's strength is measured in thousands of pounds per square inch. Aside from blades with very small cross-sections, no person should have the strength to break a knife in the direction where the choil creates a stress riser.
 
Keith Montgomery said:
Neither, it's pronounced ch (as in chore) - oil (as in coil).

Not sure about the stress riser thing, but I would think that plunges would be every bit as likely to cause weakened areas as would any of the other things mentioned.
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The drop in cross sectional area formed by the plunges would cause an area that is likely to fail in shear stress, rather than normal stress like the choil would experience. The plunge is still a potential weak spot, but as I stated in the above post, not likely to be a point of failure under the forces of a human.
 
My point is that the features (maker's stamp, spine notches etc.) described in the initial post would be insignificant, as other factors that would most likely contribute to failure first under EXTREME duress.
 
Kevin Jones said:
My point is that the features (maker's stamp, spine notches etc.) described in the initial post would be insignificant, as other factors that would most likely contribute to failure first under EXTREME duress.
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I think it depends on the maker. If proper attention is paid then the stress risers can be minimized. I won't cite any specific examples but I've seen plunges ground straight across the width of the blade, filework on the spine, even holes drilled through the blade that may have been the weakest point. If a maker tests his designs then he should know if his blades are being weakened significantly.
 
Steven Roos said:
A sharp choil is a stress riser, and can multiply the stresses at that point by many times what the stress would be in the bulk blade material, but is it honestly a problem? Even the poorest quality steel's strength is measured in thousands of pounds per square inch. Aside from blades with very small cross-sections, no person should have the strength to break a knife in the direction where the choil creates a stress riser.
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That's always been my understanding of it.

Roger
 
Steven Roos said:
The drop in cross sectional area formed by the plunges would cause an area that is likely to fail in shear stress, rather than normal stress like the choil would experience. The plunge is still a potential weak spot, but as I stated in the above post, not likely to be a point of failure under the forces of a human.
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I personally don't think any of the things mentioned would cause weak areas that would be a problem during normal, or even heavy use. Problematic stress risers are caused by not getting all the irregularities out of the blade before the quench. I have chopped very hard wood with knives that have choils and stamped marker's marks, and never had one break. Never have done it with a knife that had a thumb ramp, but did chop with a knife that had a saw, and it never broke. My guess is that if a blade breaks during use it is probably because something was not done right when preparing the knife for heat treating, or that the heat treating itself was not done properly.
 
Like I said, there would be no problem under the power of a human hand, but there is no denying that the stresses are magnified at the plunges, choil, etc.
 
2knife said:
So, I take it there is no significant weakness caused by a maker's stamp? .. the reading in "How to make knives", indicated that Loveless thought it created a stress riser to stamp a blade. (or maybe i read it wrong?) :confused:
David
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I think he is just being cautious. It is a possibility, albeit, a very small one, so he has decided to avoid it.
 
2knife said:
So, I take it there is no significant weakness caused by a maker's stamp? .. the reading in "How to make knives", indicated that Loveless thought it created a stress riser to stamp a blade. (or maybe i read it wrong?) :confused:
David
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There is a stress riser created by the stamp, but I doubt it would be a problem with the amount of force a human could apply.

On a somewhat related note, I fixed a pair of eyeglasses today that broke in a very specific spot. If you've ever noticed the numbers on the nosebridge of your eyeglass frames, you may find that they are stamped into the metal. This pair broke right though the right side of the zero in 50. Stress risers at work!
 
Loveless is Correct. I have a Case Pocket knife in front of that if cracked right down the center of the blade length wise. It started in the "S" of Case. Is this common" No.. But it can happen. Loveless never said that stress risers would ruin all knives. It is however something we as maker need to be aware of.

Saw teeth. especially the ones like the ones in the Lile Rambo Knife can and will cause a break in a blade. Some times in the quench. Wild file art is very prone to cracking on thin bladed pocket knives that are actual used. I can'[t tell you how many I have had brought to the shop with broken blades. (Mostly factory knives that were filled). Now when you consider that the factory knives I saw broken had to be pretty soft in the first place to even be filed-well, What would happen in a very hard blade. "SNAP"!!! For many years the stress risers caused by round tang construction was a very real problem. Today, makers use a much wider tang area next to the blade. Many radius this area for strength. This has helped a lot. (Remember the old British Commando Knife)? It was famous for snapping at the guard joint!

Lastly, remember that a stress riser caused in heat treat and one cause by notching are two different things. One can be fixed by normalizing. The other cannot. It is call notch sensitivity. This is what all high carbon steel is. Look at it this way. Take a branch from a tree. Bend it until it is taunt. Now take a knife and cut a "v" notch into it about mid way. Now bend it again. You will find that the branch will shear at the notch. This is what we are talking about when we say notch sensitivity. And yes. This is also a stress riser. Mike
 
Almost all fully hardened knives break at either the tip or the stamp.
A good reason to etch(laser, acid) or engrave the mark on "fully hardened" pieces.

(I have broken more than my limit..)
 
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