Why buff knives?

[SShepherd]

So my question for you is, where is your proof that it doesn't have an effect? I've cited tons of reasons and theory behind why it does have an effect and all I've heard to the contrary is stuff like "No I don't think it has an effect."

Destraal;

Thats not how it works. The claim was made that "Buffing parallel to the blade length actually strengthens the blade when lateral force is applied. This fact has been known to the metals industry for many years and to blade smiths who test or had to make knives to be used for many more.

Now, if it's an industry fact, there should be some information as to how much improvement in streingth this surface finish gives over other finishes.
That being the case, the burden of proof is on those who made the claim- not those asking for data to back it up.
Also, if buffing increases the streingth, wouldn't that make the etched surface of a damascus blade the absolute worst surface for blade streingth?

 

[Ed Fowler]

When makers actually do their own performance testing on their knives, testing a representative sample to destruction we find many "theories" of value that others feel really doesn't make a difference.

If you do not wish to do your own experiments on your blades that you have made in your shop you are asking a lot for those who do experiment and test to prove their methods to you, you cannot expect those who do their homework to spoon feed you.

I mentioned one of many reasons to buff or hand rub, provided a reference and you are free to do as your chose.

Destral: I like your style, thanks for adding your thoughts.

George: it is a pleasure to share thoughts with someone who has been there!

 

[Destraal]

Hopefully someone has some of this data. I could almost certainly find it if I had the drive to sift through all the technical papers I'd run across. Out of curiosity, have you looked at that article I mentioned in my last post? Do my previous posts explaining the underlying mechanisms for that claim make sense to you? I'm happy to try and explain better, but if you're ignoring the meat of my posts and blindly asking for empirical data then I'd rather spend my time doing something else.

The counter argument that buffing lengthwise does not increase performance of the blade has been made as well, and I have seen no proof supporting their argument, nor even a random reason. If one side of the debate gives a list of reasons why their point is valid, and the other merely says "nuh uh" then who do you do you think is really contributing? I realize that you weren't the one to make the counter argument, but if the other side can't even provide a reason for their point then I see no need for me to even look for this evidence you want.

Destraal;

Thats not how it works.

Says who? I've shown how that claim is reasonable, those making outlandish claims that buffing lengthwise has absolutely no effect should at least provide some reason for their position.

Ever seen any sort of manufacturing plant use Damascus in their machines? I've never seen anyone make the claim that Damascus makes a stronger blade. What it does is make a pretty looking blade and there's much debate about whether it creates better edge holding properties, but that's a topic for another thread.

 

[james terrio]

A knife blade is not intended to, and never will go through the stresses a propellor does. (Unless maybe, that Noss fellow gets hold of it ) The ditch in front of my house is not carved from rock, and wouldn't last a day in the face of a river. Hence the admittedly clumsy analogy.

Seems to be different definitions of the word "reasonable". My claim, outlandish or not, is that buffing up down or diagonally would have so little demonstrable effect on a knife blade as to be irrelelvant.

I uderstand about stress risers. But if a scratch from a buffer causes your blade to crack, you have way more serious problems than whether or not it's shiny.

I think the whole thread-drift is another example of making mountains of molehills. There's an awful lot of empirical evidence around regarding HT techniques, the strength of various alloys, etc, specifically in knife blades, and thank goodness for that! Just saying something might be true doesn't make it true.

 

[Destraal]

Is anyone actually going to come up with empirical evidence showing that sanding or buffing a knife blade lengthwise vs. perpendicular has ANY effect at all on its strength?!?

From this statement I assumed you meant that you thought that buffing lengthwise vs perpendicular didn't have ANY effect. Not that it had such a small effect that it was negligible. My apologies for the misunderstanding. However, I addressed the possibility that you meant otherwise in my following post:

If you had said that you believe that the effect is negligible and not worth the effort, then I would've agreed with you, but you're implying there is absolutely no effect, with no proof what-so-ever.

A knife blade is not intended to, and never will go through the stresses a propellor does. (Unless maybe, that Noss fellow gets hold of it )

You're right, but over a life time of use, or a shorter time of heavy use, a knife blade can go through as many loading cycles as a propellor (assuming that propellors have well defined times that they're to be replaced like many parts in aircrafts).
Even at a low stress, given sufficient loading and unloading cycles, a blade can suffer a fatigue failure. Of course there is a threshold where this doesn't occur, but given the small cross sectional area of most blades it would only require a fairly small amount of force to pass this threshold.

I think the whole thread-drift is another example of making mountains of molehills. There's an awful lot of empirical evidence around regarding HT techniques, the strength of various alloys, etc, specifically in knife blades, and thank goodness for that! Just saying something might be true doesn't make it true.

The topic of the thread is "Why buff knives?" This is one of those reasons, at least for situations where higher than usual performance is a necessity. Doesn't mean that all knives have to be buffed, you can obviously make a very good knife that will last wonderfully with normal use, and you probably won't be missing much at all.

Destral: I like your style, thanks for adding your thoughts.

Thanks, if it wasn't for you I probably wouldn't have ever even thought about buffing as a potential method for increasing performance of a blade.

 

[SShepherd]

Hopefully someone has some of this data. I could almost certainly find it if I had the drive to sift through all the technical papers I'd run across. Out of curiosity, have you looked at that article I mentioned in my last post? Do my previous posts explaining the underlying mechanisms for that claim make sense to you? I'm happy to try and explain better, but if you're ignoring the meat of my posts and blindly asking for empirical data then I'd rather spend my time doing something else.

The counter argument that buffing lengthwise does not increase performance of the blade has been made as well, and I have seen no proof supporting their argument, nor even a random reason. If one side of the debate gives a list of reasons why their point is valid, and the other merely says "nuh uh" then who do you do you think is really contributing? I realize that you weren't the one to make the counter argument, but if the other side can't even provide a reason for their point then I see no need for me to even look for this evidence you want.


Says who? I've shown how that claim is reasonable, those making outlandish claims that buffing lengthwise has absolutely no effect should at least provide some reason for their position.

Ever seen any sort of manufacturing plant use Damascus in their machines? I've never seen anyone make the claim that Damascus makes a stronger blade. What it does is make a pretty looking blade and there's much debate about whether it creates better edge holding properties, but that's a topic for another thread.

Destrall;
I'm not intending this to turn into a pissing match. The burden of proof is on the claim that a surface buffed leingthwise increases streingth. We're discussing a mirror polish, not "scratches" normally associated with stress risers. Somehow if you feel asking for a ammount of increase this provides is outlandish- or that we simply need to do our own testing on a claim that has been said is an industry "fact" seems suspicious in its self. I don't think many of us have the equipment capable of doing such a test accurately.

again, were talking about knife blades---- not propellers (which you keep refering to). My reference to the surface finish of a damascus blade is very relevant to the discussion.

 

[Destraal]

Destrall;
I'm not intending this to turn into a pissing match. The burden of proof is on the claim that a surface buffed leingthwise increases streingth. We're discussing a mirror polish, not "scratches" normally associated with stress risers. Somehow if you feel asking for a ammount of increase this provides is outlandish- or that we simply need to do our own testing on a claim that has been said is an industry "fact" seems suspicious in its self. I don't think many of us have the equipment capable of doing such a test accurately.

again, were talking about knife blades---- not propellers (which you keep refering to). My reference to the surface finish of a damascus blade is very relevant to the discussion.

I have a very hard time believing that you're actually reading my posts. Especially since you haven't told me whether you've even looked at the source I mentioned, nor did you mention that you read my posts. It seems you skim very lightly and pick on some issue that I addressed either earlier in that post or in another post I've made.

I've explained in detail why propellor blades are a valid comparison and all you say is something to the tune of "no they aren't." You have yet to mention which of my reasons you think are wrong and why.

Mirror polishes have scratches too, but they're small enough and uniform enough that you can't see them with the naked eye.

As for Damascus, I was meaning that just the edge holding qualities of Damascus are a subject for another thread. I also pointed out that no one has said that Damascus makes a stronger knife laterally. You pointed out that if the scratches were weaknesses then the etching on Damascus would also be a weakness, and I basically agreed with you that etched Damascus wouldn't be stronger. I didn't say it directly but it was very heavily implied that that was what I thought.

Please read the posts if you're going to comment on them, repeating myself tends to make me cranky.

 

[SShepherd]

I've read every post, and even looked at your "sources"

I've asked multiple times for a measurable increase to back up the claims.
While a prop my benefit from a surface finish, it hardly translates into any quantifiable improvement in a hand tool/knife. The stresses that a prop operates under are by far larger and more complex than that a knifeblade are put under.
Now you've decided to insult me, and that makes me "cranky":grumpy:

untill I see some hard data on how this increases the streingth of a knife under normal use, I'll hold off on filing this "fact" in the unsubstantiated claims and hype drawer

Have a nice day

 

[Destraal]

I've read every post, and even looked at your "sources"

I've asked multiple times for a measurable increase to back up the claims.
While a prop my benefit from a surface finish, it hardly translates into any quantifiable improvement in a hand tool/knife. The stresses that a prop operates under are by far larger and more complex than that a knifeblade are put under.
Now you've decided to insult me, and that makes me "cranky":grumpy:

untill I see some hard data on how this increases the streingth of a knife under normal use, I'll hold off on filing this "fact" in the unsubstantiated claims and hype drawer

Have a nice day

I did not mean to insult you as a person just stated that based in your responses it was unlikely that you were actually reading my posts. The fact that you bring up the stresses on a propellor blade again after I addressed that in post #65 seems to substantiate that claim.

However, implying that the source I provided wasn't valid is an insult to me. It deals specifically with steel specimens in fatigue, there's no mention of propellor blades in it. Not to mention that the one source had tons of additional references that you would've needed looking into in order to definitely say your answer wasn't there.
As for the states of stress that a propellor blade experiences, I doubt that a propellor blade sees as many different loadings as a knife does since the propellor is used for one thing and a knife can and is used for thousands of tasks.

I think that we can agree that this argument is getting out of hand and that we should probably stop at this point.

 

[james terrio]

From this statement I assumed you meant that you thought that buffing lengthwise vs perpendicular didn't have ANY effect. Not that it had such a small effect that it was negligible. My apologies for the misunderstanding.

I'm the one to apologize, the misunderstanding is due to me using the wrong word. You're correct that I should have said "negligible" instead of "any" in the first place.

I would still love to see test data on this. No pissing match needed I will wager one of my own handmade knives that all other factors being equal, the direction of buffing or hand-sanding will make a difference measured in tenths of a percent or less, as far as how quickly the blade fails.

 

[Ed Fowler]

From the emails I have received several have ordered the book about the prevention of fatigue failure of metals under repeated stress, a few heard the message. This alone makes the time invested on this thread worthwhile.

The fracture in the propeller blade that broke was caused when someone lightly stamped a number on the blade, this seemingly insignificant event was the source of the stress raiser that killed all on the aircraft. Recently we tested a blade on a folder that cost over $200. It snapped easily under a load that did not register on our torque wrench. A catastrophic failure that resulted in a blade that started out as a 3 inches long and ended up with a blade less than 1/4 inch protruding from the handle the stress raiser was the makers name etched on the blade.

The knowledge to better blades is readily available to those who want to make knives that have the potential to serve their owners reliably, all we as makers need to do is read, test and those who pay attentin will make better blades. We can learn by looking at the knives of history, knowledge can come from many venues, studies of the products of nature such as birds, fish and plants. We can learn from studies of boat designs and other engineering texts. Knives are simple tools and unfortunately do not generate enough revenue to finance a lot of scientific evaluation, thus the significance of the knowledge from other venues.

Destral: I would appreciate it if you would list your most favorite reference book so I could order one and I thank you for your participation in this disucssion. You have a lot more patience than I do.

 

[Sam Salvati]

MMM mmm that's some good kool aid you peddlin'

 

[SShepherd]

You have a lot more patience than I do.

Sorry for you're loss of patience Mr.Fowler, but I expect anyone who makes a claim as fact or "industry standard" to back it up with evidence as it pertains to the subject at hand- regardless of who said it. I've recieved many emails from people with the opinion that a mirror polish has no bearing on the streingth of a knife blade.

I've been carefull to neither agree or disagree, but simply look for clarification as to an ammount of increase of streingth a mirror polish produced. I guess I expected a number, not a reference to a $150 dollar book that might or might not give me the answer. I'll keep searching the web, as these days my $150 can be better used for buying steel .

 

[Ed Fowler]

I never mentioned a mirror polish, where did that come from?

I have and still do commit 10% of my income to books, I have never regretted the investment. Along with that goes a budget of my time, 2 hours a day to read.

We also have a library that has access to libraries across the nation for the loan of books they don't have.

I could come up with numbers, but they would be meaningless to you as the experiment had to do with something other than knives.

I would suggest that you do as we did, make a couple of knives one buffed each way and compare your results by testing the knives to destruction. Then you will know how buffing can influence the performance of your blades with your methods and steel.

 

[2Edgy4u]

I never mentioned a mirror polish, where did that come from?

I have and still do commit 10% of my income to books, I have never regretted the investment. Along with that goes a budget of my time, 2 hours a day to read.

We also have a library that has access to libraries across the nation for the loan of books they don't have.

I could come up with numbers, but they would be meaningless to you as the experiment had to do with something other than knives.

'I would suggest that you do as we did, make a couple of knives one buffed each way and compare your results by testing the knives to destruction. Then you will know how buffing can influence the performance of your blades with your methods and steel.

'
I remember doing just as your last comment mentions close to 30 years ago. At the opening of a place called "The Piney Woods Hammer-in" in Texarkansas. One of my Mentors on the subject was Mr. Bill Moran, the other Jim Crowell. Its now known as The ABS. We tested, and we broke blades many times during the classes. Ya sure can learn Alot from what makes blades break. Enjoy. edgy.:thumbup:
Just my 2 cents.

 

[Sam Salvati]

I could come up with numbers, but they would be meaningless to you as the experiment had to do with something other than knives.

so by your logic then, that book has nothing to do with the discussion anyway?

 

[Nathan the Machinist]

Oh oh, can I get in the dog pile!?

Not 100% relevant:

The effect of surface finish, direction of lay and latent stressors in the surface of a part remaining from manufacturing processes are well known in industry and are frequently controlled in things like aerospace class work. Speeds, feeds and the type of cutter you are allowed to use to make a cut can be specified. The effect of things like shot peening, wire brushing (and perhaps buffing) that set up a surface compression, surface finish and direction of lay are basic undergraduate level material in materials and processes subjects. Applying a particular finish in a particular direction on a stressed component is very common. There are ANSI standards for these things.

I have seen knives fail in hard use. I have personally never seen a prop fail (and I grew up next to an airstrip and my family owns airplanes). It is my opinion that a knife in rough use is more likely to fail than a propeller, just the consequences are generally not so severe. But if you're in the business of making rough use knives (I am not) then surface finish, direction of lay, and residual surface stressors ought to be given some consideration.

It is my (not completely unlearned) opinion that buffing certain types of knives in a certain direction is probably a good idea.

I'd list references, but I'm going to grab a beer and float in the kids kiddy pool instead...

 

[Destraal]

Destral: I would appreciate it if you would list your most favorite reference book so I could order one and I thank you for your participation in this disucssion. You have a lot more patience than I do.

Mr. Fowler, most of my knowledge comes from a variety of courses in the civil engineering curriculum at GA Tech, as well as a large number of academic papers I've read for my research into nondestructive techniques for gauging fatigue damage.

If I had to pick one book I learned the most from it would be The Science and Technology of Civil Engineering Materials by: J.Francis Young, Sidney Mindess, Robert J. Gray, and Arnon Bentur, which is technically a textbook. I would highly recommend it though, it has a great deal of information about fracture mechanics and failure mechanisms. It also has chapters on structural steel, concrete, polymers, and wood. Obviously the chapter on concrete will be useless to any knifemaking application, but the other 3 have some potential for use in knifemaking.

It's one of the books I've held onto, and that says something.

Applying a particular finish in a particular direction on a stressed component is very common. There are ANSI standards for these things.

ASTM also mentions surface finishes in section E8.6.1.4 with regard to tension testing. I haven't looked into much else, but I would imagine that this also applies to fatigue testing.

 

[Ed Fowler]

Thank you Destral and Nathan, your experience is welcome. Edgy those were the good old days when testing to destruction was considered an essential part of the blade smiths art.

I just remembered an experiment Dick IIams and I did in the early 80's.
Two blades from the same bar of steel, forged, ground, differentially hardened and tempered one after the other in no particular order.
One buffed horizontally, the other parallel to the blade using a 500 grit buff.
Horizontally buffed blade the hardened zone cracked at about 40 degrees of flex.
Parallel buffed blade made 3 90 degree flexes, then cracked through the hard zone.

Only one experiment, we never took the time to duplicate it but it was enough for us to make our decision to buff parallel to the blade.

Destral, interesting that you mentioned cement, it was through my noticing how some cement curbing was deteriorating that helped me understand why the matrix of hardened blade is important. Uniform fine grain is more brittle than a fine uniform matrix of (for example) ASTM 10 and finer, the and finer is very significant.

By the way, please call me Ed and thank you for the refference, will order a copy tonight.

 

[Ed Fowler]

Destral: I located the book you recommended for sale on Abe Books. Prices ranged from $25.00 to $218.00. I ordered a clean copy for $33.00, it is on the way. I look forward to it and thank you for the reference.