How Can the Blade Be Strong?

S

South

Joined
Jul 31, 2007
Messages
87
Not trying to open a can of worms, but have a question about the blade on Spydercos. I've had a number of them over the years and have never had a problem, but I've not used a knife hard...

I was looking at my Para Military 2 and realized, with the hole in the blade, I'm surprised the blades don't break through moderate use. Not only am I surprised there aren't significant stress risers (that I know of), but there is not that much steel at base of the blade and the steel that's there is thin.

I'm hoping there won't emotional responses from anyone overly defensive about their knife and feeling like they're being attacked. (I have a family member that reacts like that.) I'm not attacking anyone or a knife. I'm genuinely curious as to why it's still considered strong. I've not read of any reports of them snapping at the hole, so it's evidently not a problem. I know there can be stress risers in some blades with thumb studs and there can be other factors/blade shap/geometry causing them. I'm referring to the Spyderco blade and hole specifically..

I still like my Spydercos, etc. and all that...
 
The blade isn't going to break because of the hole.

Some Spyderco's do have a great deal of distal taper(Military, Para, etc..), leaving them with a thin tip. You have to put that much distal taper in one if you want it to be a super slicer.
Spyderco also makes knives with a thicker tip if that is what one wants, but they will not cut as well.

You just can't get it all in one type of blade grind. That's why we need all types of knives.

Don't worry one bit about the hole though. Never seen, and doubt I will ever see one that breaks at that point.
 
I agree. It all comes down to what you use your knife for. "Most" Spydcos are used or slicing, not batoning. There are a few heavier duty models but in the end, a folder is a folder and the blade is rarely the weak point.

Ken
 
I had 1 outta 13 spydercos break at the hole, it was a an early Spyderco Centofontane collaboration and it snapped at the hole as I was tryin' to slice a hunck of cold cheddar cheese off the block, sent it back to Spyderco and because it was no longer in production they credited me the MSRP value of the knife, I wound up with a SS Dragonfly and an FRN Mini Dyad.

When I can afford it, I'll buy more, I did manage to get a replacement from a member here on the forums.
 
Over the years, I've seen photos posted of perhaps half a dozen Spydercos, tops, where the blades broke at the hole. Whether any of them broke due to stress risers, or anything else other than ham-fisted abuse, is a matter of conjecture. Would the blade be stronger without the hole, sure. Would it work as well, not hardly. AFAIK, round holes are the least likely source of stress risers. Sharp corners are the most likely culprits. So, if I was going to worry anything, I'd worry more about jimping than the Spyderhole.
 
As far as stress in the cutting direction is concerned, the hole is pretty much a non-issue. As long as the outer shape of the blade is maintained you can eat out the entire middle section and have very little effect on overall strength.

If you're talking about prying, the hole will make some difference, but probably not as much as you might think. The widest part of the blade, the spine, is the same as it would have been without the hole. Think about a steel I-beam, it's much stronger than a solid bar using the same amount of material in smaller dimensions.
I expect there is a range where if you stick the blade in a vice and snap it off, the blade would break at the hole, but the closer you get to the tip the less likely it will be that the blade is stronger than spine at the hole.
 
Speaking as a structural engineer here-
the hole is pretty large meaning it has a very gradual radius so it doesn't have much affect as a stress riser, but it obviously does take out a lot of material. For a knife such as my Para 2 the thicker material at the very top of the spine has reduced value in strengthening the blade because it doesn't connect directly into the spine around the pivot. Some other models have different blade shapes. I was pretty amazed though when I first looked at my Para 2 how thin the blade was at the bottom of the hole, but I had not heard of problems with this and intended to use the knife for slicing and not prying anyway. At some times in the past I had carried a Benchmade AFCK and it has a relatively thin blade, but overall it is thicker than the effective blade thickness of the Para 2.

If you stick the tip of the blade into a gap and start prying sideways, the weak point will typically be near the tip and not near the pivot. I haven't read about very many instances of broken blades recently except for one person that snapped the tip off of a Tenacious and obviously that one broke at the tip and not at the hole.

Even when using the knife just for slicing there can be some lateral loads applied to the blade. Someone mentioned slicing hard cheese- the nature of using your hands to push cut through hard materials will usually apply some lateral loads too, and if the lateral loads are enough then a blade can break. In the case of the cheese, the bulk of the blade is probably in the cheese and not just the tip, so the tip being the weakest part probably doesn't enter into it.
 
The blade cannot help but be a lot weaker than it would have been without the hole. It is still plenty strong enough for any normal and even 'hard' use. I used to worry about the Military especially (large hole, blade not very wide) but the knife has proven itself beyond any doubt.
 
Here is another question that I've wondered about since I started reading forums online. Why does the blade need to be strong? Sharp and thin will cut with less effort than sharp and thick since the material being cut is not displaced as much. The width of the blade is usually several times the thickness, making it far stronger in the direction intended for application of force than laterally whether there is a hole in the blade or not.

I've used slipjoints with blades far thinner than anything Spyderco offers hard enough to make people cringe without breaking them.
 
bdmicarta said:
... Someone mentioned slicing hard cheese- the nature of using your hands to push cut through hard materials will usually apply some lateral loads too, and if the lateral loads are enough then a blade can break. In the case of the cheese, the bulk of the blade is probably in the cheese and not just the tip, so the tip being the weakest part probably doesn't enter into it.
Click to expand...

That was me, that paticular Spyderco has a very narrow, thin blade and a fairly large openin' in proportion to the rest of the blade and in comparrison to the other patterns and when it broke it was entirely wedged into the block of cheese and I tried to pry the cheese chunk off with a lot of lateral pressure.

The openin' hole was right at the edge of the cheese and acted like the pivot point, in my book that was my fault but Spyderco took care of me, even without a reciept or proof of purchase, I had the knife so long it was outta production when I returned it.
 
bdmicarta,

You stated almost exactly the concepts I was considering, but you articulated it much better! Thanks. I've seen various materials, including some metals buckle due to lateral stresses applied while under a vertical load.

My reason for something like a Military or Para Military is mainly for backup defense. Reading the thread by traumadoc about his encounter with the attacking dogs has caused me to reevaluate the knife or knives I carry. In a defensive application, it's very easy to have lateral and hard vertical stresses on the blade. Even twisting forces can occur.

The question is evidently out of the ordinary for many users, but I don't buy large folders for slicing tomatoes, apples, roofing material, flooring or to even whittle. 90% of the reason I have them is for one reason. That's why I'm asking. (As a matter of fact, the geometry of the Military and Para Military 2 is ideal for kitchen applications. It's similar to some of our kitchen knives!)

With the amount of material absent in the area of the large hole, I was also noticing how thin the remaining material actually is.

I'm not saying the Military, etc. would fail in those situations, just asking questions. Maybe it's fine.
 
Last edited:
mkjellgren said:
This!! And that particular hole is under FAR more stress in normal use than the spyderhole ever would be.
Click to expand...

This is a very good point. It's a much smaller hole, though.

Speaking of the Para Military 2, considering it's features, the feel, etc., that knife feels like the sum is greater than it's parts. It is a great knife.
 
mkjellgren said:
This!! And that particular hole is under FAR more stress in normal use than the spyderhole ever would be.
Click to expand...

Depending on the bolster design and such it is likely that the blade will transfer forces from prying to the handle scales in such a way that the bending stresses in the blade will be lower right at the pivot, maybe as low as half of the maximum stress elsewhere. (I could draw pictures illustrating this.) The maximum lateral bending stress in the blade will occur right at the beginning of the frame or at some point slightly inside of the handle.
 
I think the P2 could benefit from a slightly smaller hole. Not enough meat up where the jimping is for my aesthetics. A mm or two less on the hole diameter would be my preference. Purely subjective I guess, I EDC an old Endura with a 12mm hole.
 
Of course removing material from the stock thickness makes the blade weaker. There is a greater amount removed by the blade grind, and not many would recommend that be elimated to increase the strength of a folding knife. It ain't a spyderco without a spyderhole.
 
shunsui said:
I think the P2 could benefit from a slightly smaller hole. Not enough meat up where the jimping is for my aesthetics. A mm or two less on the hole diameter would be my preference. Purely subjective I guess, I EDC an old Endura with a 12mm hole.
Click to expand...

I would be curious how most people feel about the size of the hole. I have fairly big hands but they aren't fat and beefy like some people. My thumb fits in the hole with lots of room to spare so my first impression was that the hole was too big. I wonder how many people would think it is just right and would be too small if reduced.
 
I agree that the effects of the spydie hole is minimal when the folder is used for its intended purposes. However I see the same cannot be said about the SogZilla which has a design flaw. :)
 
shunsui said:
I think the P2 could benefit from a slightly smaller hole. Not enough meat up where the jimping is for my aesthetics. A mm or two less on the hole diameter would be my preference. Purely subjective I guess, I EDC an old Endura with a 12mm hole.
Click to expand...

I would rather the blade be bigger overall than have a smaller hole, IMO the hole on the Para 2 is just about perfect the way it is. I personally wouldn't mind if the hole were bigger (but then, I always want everything bigger), so if it's still a little small for me then it's probably just right for most people.
 
You must log in or register to reply here.
Back
Top