Weird question, bent blade

Rsmith_77

Rsmith_77

Joined
Jun 4, 2010
Messages
4,250
I've noticed something strange about my GEC 85
you cannot see it by eyeballing it (or i cant)
but i've noticed if i lay the blade flat on a flat surface (table, or strop) that it has a very slight curve to one side, perhaps the last 1/8" inch

now i am slightly ocd but this isnt really bothering me, i am just curious if this is fairly common or not
i cannot see how its going to affect its use, but i figure you guys got lots more experience than i do and it couldnt hurt to ask.

I seem to recall a thread some time back about this, but my google-fu seems to be weak.

anyways, enlighten me folks
:D
 
It must be the wind... :p
Since you don't have any picture, I have a question. Is all the blade bent, or you see it bent more on the spine side (or edge side)?

Fausto
:cool:
 
I just checked my 85 real harness jack with a business card, the etch side is perfectly flat from plunge to tip, the other side curves away from the card 1/2 inch from the tip, about 1/32nd.:eek: The spine is dead straight, must be in the grind.

Best regards

Robin
 
i just cant seem to get a good pic
must be too dark in the house or something.

the (very slight) bend is past the swedge. basically just the last 1/8" of the blade, it curves inwards just slightly

like pipeman, the etch side is perfect, the other side basically bends just a bit at the tip
 
That's what I was thinking about; it sounded more like a matter of blade grind.
I wouldn't call it a problem obviously; I assume these things do happen and should be considered "normal" :)

Fausto
:cool:
 
It's all from mid width about 1/2 inch back from the tip and down toward the edge. Quite strange because the edge is dead straight from tang to tip as is the spine.:confused:

REgards

Robin
 
It's very, very common on pocketknives. Most people will see a 'straight' blade most of the time, when eye-balling a knife. But, if actually laid alongside a true straight edge, like a steel ruler, there will almost always be a little bend or curve to virtually all blades. Could be the grind, or a little warp from the heat treat & quench, or any combination of the two. An asymmetrical grind would likely be more visibly affected by the warpage during heat treat anyway, due to the uneven rate at which each side of the blade cools down. Multi-bladed folders, with more blades than backsprings, such as a 3-bladed stockman on 2 springs, will usually have at least one 'crinked' (or 'krinked'; forget which spelling applies) blade, which is deliberately bent to make adjacent blades fit into the blade well of the handle.

I've noticed this a lot more on basic carbon steel blades, for some reason. Maybe something to do with how the steel reacts to the heat treat & quench, I don't know for sure. Seems to be more prone to warping than stainless blades, especially on very thin blades.



David
 
Last edited:
This is kind of hard to explain, but when a blade is ground, in order to retain the edge as the blade curves up to the tip, a cam is employed to force the last few sixteenths of the blade into the grinding wheel. At the same time the blade is usually pivoted a bit into the wheel, again to retain that thin edge as the blade curves up. This is usually more pronounced on the pile side as that's usually the last side to be ground. Gives the illusion that the blade has been bent but it's really most often just the grind.

Eric

PS-n This is most noticeable on clip blades due to the geometry of the tip.
 
Last edited:
Obsessed with Edges said:
I've noticed this a lot more on basic carbon steel blades, for some reason. Maybe something to do with how the steel reacts to the heat treat & quench, I don't know for sure. Seems to be more prone to warping than stainless blades, especially on very thin blades.



David
Click to expand...

yeah i tried all my carbon blades and they all have the curve at the tip, the soddie jr, the shrade 123OT, my gec, my opinel etc etc
(didnt have the heart to try my texas jack yet though)

obviously it isnt anything to worry about, just wanted to make sure :p
 
My Uncle Henry 897UH is a stockman, but the last 1/4" or so of the clip blade has a slight bend inwards, which is strange because there is no krink needed at just the end. I couldn't tell you what it is for, and I know I haven't used it as a pry bar.

Connor
 
The heat treat would have nothing to do with that curve since the blades are treated before they're ground. It'd take an awful lot of force to warp the last 1/8" of a .070 to .090 piece of steel without turning the rest of it into a pretzel. See post #9.

Crinking is done at the shoulder or plunge of the blade since this is usually annealed softer along with the tang.

Eric
 
Last edited:
ea42 said:
The heat treat would have nothing to do with that curve since the blades are treated before they're ground. It'd take an awful lot of force to warp the last 1/8" of a .070 to .090 piece of steel without turning the rest of it into a pretzel. See post #9.

Crinking is done at the shoulder or plunge of the blade since this is usually annealed softer along with the tang.

Eric
Click to expand...

Case does the primary grind (overall blade profile) before heat treat. The finished edge is done afterwards. Would seem to make sense, in terms of saving wear & tear on their tooling. This was demonstrated in a video in the 'How it's Made' series about Case pocketknife production, posted here occasionally in other threads. There's a segment in that video showing bins full of pre-ground blades being fed via conveyor into their furnace.


David
 
Yes, that's the blade blank. In general, it goes in this order: 1-Blade blanks are cut, punched, or lasered from a piece of steel. 2- Blanks are then drilled (this is sometimes done in step one depending in the cutting method), tang stamped, and have nail marks cut or punched in their soft state. 3- blanks are then heat treated 4. After heat treat, the blade is ground to a blunt edge, this is where that kind of curve mentioned by the OP is produced, especially on the clip blades. It's just a product of getting the tip of the blade ground to an edge. This can be tweaked to lessen the effect, but you're almost always going to have a bit since you're trying to create that edge with the pile side grind, so you've got to meet up with the mark side cut. If you don't cut in at the tip you'll wind up with a tip that's too blunted. Like I said it's REALLY hard to explain. I'll try to snap some pics of the process if I get a chance this week.

Eric
 
That seems counter-intuitive, IMO. Wouldn't grinding the blades be much harder on the equipment once they are heat-treated? I've always been under the impression that HT comes after the blades are ground to blanks,* especially since the grinding process can potentially ruin the HT.
...but I could be wrong.


*I've always understood a "blank" to be a blade that's stamped/cut, ground to roughly the finished shape, and drilled. Everything except hardening and sharpening. Is that not the case?
 
Here's a recent photo from GEC titled "#74 off to heat treat." As you can see, the blades are blanked, drilled and stamped, but not ground.

630.jpg
 
i think i got a couple pics
been trying to get something to show

anyways, this is what i am talking about
one with flash, one without
wasnt sure which one would come out better

oh and for the record
i know its not going to affect my knife, it wont cut bad or it wont affect it in any way
but i truly believe its because the blade is bent slightly

002-30.jpg


001-33.jpg
 
puukkoman said:
That seems counter-intuitive, IMO. Wouldn't grinding the blades be much harder on the equipment once they are heat-treated? I've always been under the impression that HT comes after the blades are ground to blanks,* especially since the grinding process can potentially ruin the HT.
...but I could be wrong.


*I've always understood a "blank" to be a blade that's stamped/cut, ground to roughly the finished shape, and drilled. Everything except hardening and sharpening. Is that not the case?
Click to expand...


Cutleries have always done the heat treat first, it goes back to the days of 1095 blades and older grind stones. The old stones were made up of abrasives held in place by sulfur (which also acted as a lubricant). If soft 1095 were ground on the stones they'd get loaded up with steel sludge. Once the blades were heat treated you wouldn't have this problem because of the hardness and the change in the chemical makeup of the steel. On top of that by grinding first you also have the problem of warpage of the thinner edges during heat treat and quench. This is avoide by treating a thick, uniform blank. If the blank does happen to warp a bit the grinding process can even it out. Then there's the chance, if grinding first, of putting a deep gouge in the soft steel blades while they're being banged around in boxes and tossed into baskets. in contrast, there are no sharp edges on the blanks, and most of their surface gets ground away anyhow. The commercial blade grinders are made for grinding hardened steels. They grind the blades in a shower of coolant that keeps the blades quite cool while they're being ground, just a bit warm to the touch right off the wheel, so there's no danger of ruining the heat treat.


Rsmith, I'm almost certain that's a product of the grind, you can see that the mark side is quite straight. You could also get a little curve like that from an uneven swedge, although it likely wouldn't be that pronounced so close to the point. Still haven't had a chance to get photos of the grinding process, I'll try Monday.

Eric
 
Last edited:
The blank is the stamped blade shape, which is blanked out of roll steel by a large multi ton press. They're usually slightly oversize so that once they're ground the backs, round ends, front tang and run-ups can be dressed to gauge. Fine blanking presses will cut extremely accurate and smooth blanks that need no dressing. Once the blank is ground to a near edge, it's no longer a blank, it's a blade. Here are a few examples of blanks, the top 7OT is fine blanked versus the UH below it (which is also heat treated):

30j486p.jpg
[/IMG]

Eric
 
ea42 said:
This is kind of hard to explain, but when a blade is ground, in order to retain the edge as the blade curves up to the tip, a cam is employed to force the last few sixteenths of the blade into the grinding wheel. At the same time the blade is usually pivoted a bit into the wheel, again to retain that thin edge as the blade curves up. This is usually more pronounced on the pile side as that's usually the last side to be ground. Gives the illusion that the blade has been bent but it's really most often just the grind.

Eric

PS-n This is most noticeable on clip blades due to the geometry of the tip.
Click to expand...

This is correct, especially on older grinding machines. Depending on the type of blade, it actually twists slightly in the grinders. And as Eric says, the point of the blade is pushed out farther against the wheel to maintain the uniform thickness of the blade.
 
You must log in or register to reply here.
Back
Top