Knife sharpening techniques.

offsetlover

offsetlover

Joined
Feb 26, 2007
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I was wondering if anyone could tell me how well (or practicle) using laser tech is in sharpening knives be it from factory or custom? i think that it would get the knife freaky freaky sharp if u use the right angle.
 
Are you thinking of cutting the steel with a laser to form the edge? It seems like you would have to do that before you heat treat the steel. I guess it would all depend on how lasers cut steel. I have thought about similar things.
 
no im not looking to do it my self. i was wondering more about how it would be done and if it was a good idea. I would think that you would do it after the heat treating. I would think that the laser would cut steal easily. I would love to see a knife that had an edge done by laser
 
I am of course, not a laser technician, but I think that lasers cut things by heating them to very high temperatures. If this is indeed how they work, then that would ruin the heat treat of the steel.

http://www.efunda.com/processes/metal_processing/laser_cutting.cfm

(for what it is worth) http://en.wikipedia.org/wiki/Laser_cutting

Some things I though were interesting about the efunda one:

1. Lasers cut by melting the material in the beam path.
2. Materials that are heat treatable will get case hardened at the cut edges.
3. Burrs are quite small compared to blanking and shearing.

#3 is especially interesting, because an utter lack of a burr would be the whole point of making an edge with a laser. #3 leads me to believe that burrs do exist on laser cut metals. It would be interesting to know exactly what size the burrs usually are.

P.S. I suppose you could try asking about it on candlepowerforums.com surly there is someone hanging around there that has a laser related education.
 
They do work by melting small amounts of metal incredibly fast, but with an incredibly well collminated lense (very focused point), and a room temperature sufficient to negate any heat transfer, it would be possible. It is however, incredibly unlikely, seeing as the laser required would cost upwards of 500k, and it would take an immense amount of time.
 
Well since you are shaping an edge, right at the edge the energy transfer will always be appreciable, and the thermal mass is tiny. In otherwords, you are shaping the edge by burning excess material off.....not a good idea.
 
JReilly said:
They do work by melting small amounts of metal incredibly fast, but with an incredibly well collminated lense (very focused point), and a room temperature sufficient to negate any heat transfer, it would be possible. It is however, incredibly unlikely, seeing as the laser required would cost upwards of 500k, and it would take an immense amount of time.
Click to expand...

Nonsense, you cannot melt metal without heat transfer.

With lasers, you are cutting by melting the metal. The laser does not vaporize the steel. It melts the steel. You are raising the temp of that edge to the melting point of the steel.
Say goodbye to your heat treat on that edge.

It is also difficult to remove melted steel smoothly from the edge. You get fine dribbles and drops. Not a good way to get a fine edge.

You can use lasers to perform the first cut to rough out your blades. Buck knives does this. Then they shape, heat treat and sharpen.
 
knarfeng said:
. The laser does not vaporize the steel.
Click to expand...

No, actually, they can. The trick that is often used in laser cutting and welding for very sensitive applications is to focus the beam in time and space. Heatconduction is a slow process, too slow to follow the pulse. This way you can heat a small spot beyond the melting point and even the boiling point of steel with relatively small amounts of energy and without apreciably heating the material around it. The problem comes when you apply this to such a small workpiece like an edge which overheats very quickly because of the small thermal mass. And then there is the little problem that these laser systems aren't exactly run of the mill.
 
HoB said:
No, actually, they can. The trick that is often used in laser cutting and welding for very sensitive applications is to focus the beam in time and space. Heatconduction is a slow process, too slow to follow the pulse. This way you can heat a small spot beyond the melting point and even the boiling point of steel with relatively small amounts of energy and without apreciably heating the material around it. The problem comes when you apply this to such a small workpiece like an edge which overheats very quickly because of the small thermal mass. And then there is the little problem that these laser systems aren't exactly run of the mill.
Click to expand...

Hey HoB,
I'm having a hard time visualizing this process working on a blade of usable size.

I will give you that you could do this with microscopic amounts of metal on a microscopic sample. I have a hard time seeing that process expanded to something the size and shape of a knife blade. The original intent was a smooth edge. You got data that shows that a gazillion such vaporizations would leave the smooth edge the man was looking for on something that big and that shape? If you say you got data, OK. (I like data. It tells you stuff that theory says should not be.)

When we cut metal in our shops with our lasers, we make allowance for edge effects made on the metal. We know we change the heat treat on the edge. We can make allowance for it on a part by making it a tad bigger than we need. Can't do that on a knife edge.
 
wow talk about alot of info. looking like it could never be done. crap lol. thanks for the info guys

HEY ITS MY 100TH POST!
 
I suppose it might be possible to find a steel that would end up (hardness wise) about where you wanted it for a knife edge after the laser cutting.

What about heat treating after the edge was shaped?

Seems like the main problems would be not hitting the edge on anything, and possibly slag. (Do steels get a coat of slag from heat treating? They defiantly do at forging temperatures.)
 
FlyingMuskrat said:
I suppose it might be possible to find a steel that would end up (hardness wise) about where you wanted it for a knife edge after the laser cutting.

What about heat treating after the edge was shaped?

Seems like the main problems would be not hitting the edge on anything, and possibly slag. (Do steels get a coat of slag from heat treating? They defiantly do at forging temperatures.)
Click to expand...

good points. anyone who has forged a blade or knows someone who has have any answers/comments?
 
Hi, knarfeng, sorry my statement was more of a general nature. The idea for edges is as you say completely nonsense for various reasons which have been already mentioned. I just wanted to point out that there are actually laser processes where the material is rather evaporated (explosively) rather than melted. In LASIK for example the tissue is not really "cut" or melted by the laser but the laser heats the water in the tissue so rapidly that you have a very minute localized steam explosion which actually ruptures the tissue. Amazing that they operated on the eye like that :D. So sorry, my response was a bit off topic. :o Must be the damn flashing green light in here, must be affecting my brain :(. As I sit here, bored out of my mind, I am babysitting my own laser, which is unfortunately not powerful enough to vaporize steel......well actually, now that I think about it....with the right lens.....well, I am sure my advisor would have a fit if she knew I would even contemplate such a thought :D.

In principle, though, this is possible to scale up, with rep rates in the kHz range. Essentially you take a few thousand shots per second.
 
OK, thousands of shots per second. But, you still gotta end up with a smooth surface. Don't think explosive vaporization could ever do that.

Reminds me of Gallagher's Sledge-a-matic routine, "even makes julian fries. But I swear you gotta hit that sucker juuuust right."
 
well what if the laser was used in the way that HoB described to get the main angle on the edge and then it was finished off some other way? maybe before the heat treat (?). you could prolly get the edge very sharp any way, but then it would become super sharp after the finishing?
 
this is basically how EDM works, and you can get amazingly smooth finishes with that. And EDM doesn't really heat the surrounding material appreciably when done right. Part of the problem I think is that you people are not thinking to scale, when we think of a "smooth" edge, we're still talking about gouges, just really small gouges. With super accurate lasers you have a theoretical size limit of the width of a photon for the impact sight, now in practice that's going to be much larger but still very very small. Now cost on the other hand...would probably be out of this world. The problem with sharpening before heat treating is cracking and warping.
 
I get nervous when people start using terms like "super acurate". It means they don't know the specifics of the process they are talking about (nor the associated problems). But, you might have an idea with the EDM methodology. That can produce a fine surface finish. You would stand a better chance of getting what you want with that process than with a laser. I think it would still be too expensive. But I am WAGging on the cost issue.

Equating EDM surface finish with that achieved with a theoretical laser technique is not an automatic assumption. There are significant differences in the two technologies.

The original question was possibility and practicality for sharpening with a laser. I think we all agree that even if it were possible to sharpen with a theoretical super laser, it is not practical. And it is not possible at all with the standard metal cutting lasers in use today.

====================
In God I trust.
All others bring data
 
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