Is a Fileworked Spring as Strong as a Non-Fileworked Spring ????

Modoc ED

Modoc ED

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Say a cutler is assembling knives and has all the parts necessary laid out on a table next to him. Everything is the same - blades from the same batch as well as the liners from the same batch, and the springs from the same batch etc.. As the cutler is progressing, on a whim, he chooses a spring at random and works it over with a file and assembles it into one of the knives he is working on. When finished assembling the knives, is the fileworked spring as strong as the springs in the other knives and is the fileworked knife as capable a user as the non-fileworked knives?

This picture is to illustrate a fileworked spring only. Nothing to do with pattern or manufacturer.

Damascus Stag Lambfoot 4 .jpg
 
fishface5 said:
NO bc less steel = less material to resist movement. But the difference depends on the amount of steel removed. Also the engagement geometry affects resistance as a separate factor.
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Could you clarify your explanation for us simple-minded folk??? :rolleyes: :oops:
 
Modoc ED said:
is the fileworked knife as capable a user
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I had a Case toothpick from the 1980s which I thought looked cool (I was younger then!!) with all this filework, but the spring was so weak it barely stayed open!!
Long gone for parts!!o_O
 
good question. i wondered that myself.
when i asked a few years ago the majority said "same" but did not elaborate.
A difference in heat treating? tempered at a lower temp to make the fileworked "softer" and springier? I dunno.

My guess is "same".
Reason:
All the Lagoules with fileworked springs.
Has anyone reported a broken backspring on their fancy Lagoule?
If they have, I didn't see the thread.
 
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I'm by no means an expert, but I would imagine, if all other factors are the same, that the non-fileworked spring would be stronger. At the same time i imagine the difference is negligible for most people, unless a lot of material was removed.
 
I've never seen one break, but then there are a lot less knives with file-worked back springs :thumbsup:
 
I would suspect that when installed in a knife the 2 springs will be equal in strength and more than strong enough.

If you pulled them out of the knives, stuck them in a vice and hung weights off them till one broke I would expect the one with filework to go first.

And like always we're presuming they are both equal quality and properly finished and treated.
 
We should put this question to French contributors perhaps? French cutlery has a lot of really high grade and good file-work (guillochage ) even on modest knives. French knives tend to be easy to open but much harder to close, so the spring is at heavy tension. None of mine have broken -touch multiple woods.

You would suspect they are weaker but perhaps different steel would be used or treated in some way after working?? Must be a quality thing.
 
In theory energy should be distributed equally across the length of the spring when its under tension. I suppose that depending on the amount of file work, the design of the file work and how deep the cuts are, each cut will be just a bit weaker than the rest of the spring, and the spring will bend just a bit more at that point, creating a stress riser. Each stress riser could in theory eventually cause fatigue cracking and failure of the spring.
Will it happen? I don't know, I've never actually seen anybody that had one break.
 
Well if you filed on any other spring would it weaken it? Would you want to file on the suspension springs of your car? Lol
It would weaken the spring because it removes material.
 
I can't help but think about the case of the I-beams used in building construction. Picture a solid beam at the same dimensions of an I-beam, it would certainly be stronger and more rigid and much, much heavier than an I-beam, in most cases unnecessarily so - which is why they're used as they are, for weight reduction. There's a common misconception that an I-beam offers more rigidity, but that's only when compared to a solid beam of the same mass which would have much less surface area.

In the case of a backspring, removing material would make it weaker, which would impact how easily it deforms and returns to its original shape, but that "weakness" may lead to a longer service life as it would seem that less energy would be required to bend it, so potentially less stress over time.

Strength is an interesting concept and I think it's important to specify the kind of strength we're talking about. There's tensile strength, compressive strength, shear strength, yield strength, flexural strength, fatigue strength, impact strength, and torsional strength. Where filework may impact some forms of strength negatively, other forms may be improved.
 
I would think a properly tempered spring that hasn’t had firework done to it may be stronger but I feel it is probably negligible in the use in a pocket knife. I am no expert but I have never seen one that was broken. Most knives that have intricate file work are knives of a higher quality and more attention has been payed to them. When the whole knife is together it works like it is supposed to. Just my $0.02. Good question though, Ed.
 
Arathol said:
In theory energy should be distributed equally across the length of the spring when its under tension. I suppose that depending on the amount of file work, the design of the file work and how deep the cuts are, each cut will be just a bit weaker than the rest of the spring, and the spring will bend just a bit more at that point, creating a stress riser. Each stress riser could in theory eventually cause fatigue cracking and failure of the spring.
Will it happen? I don't know, I've never actually seen anybody that had one break.
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I too would be very worried about Sress Risers . If any of the filing is done with 90 degree corners , the corners will create areas where high Stress Risers occur . If I was doing it , which I will not , I would use round files only . I like worked backs very much and only have a couple that I never use so I have never seen one that may have broken because of being filed . I have seen some failed shafts that broke at 90 degree corners though .

Harry
 
I beam or a wide flange beams are designed to put material where it can be most efficient for bending strengths. They are designed as a beam.

For shear strength, it is linearly related to the area of the material.

For bending, the strength increases by the depth of the material to the power of three (moment of inertia). So reduction of depth of the spring material will decrease it’s strength AND rigidity quicker.

Short answer, removal of material WILL reduce strength and stiffness of the spring.

But this is all relative. You may have more strength in the spring than necessary to provide sufficient stiffness for pull on a blade and vice versa. So filing may ‘soften’ the pull a wee bit but may never reach breaking point.

My theory of sudden snap of the springs have more to do with the material defect or steel that’s been hardened more than necessary, than a dent or a cut on the spring. Yes, springs can snap from high impact or drop or a sudden damage, but I’m talking more of those cases where you have the safe queen knives nicely wrapped in paper that goes ‘ping’ suddenly.

Or…do they harden the spring AFTER it’s been filed?
 
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