Idea for a water-flow sharpening rig

J

JohnW

Joined
Sep 11, 2000
Messages
144
The following idea occurred to me the other night, and I thought I would run it by the fellow knuts on BF:

Imagine something the shape of a large box, filled with water. Running the length of the box are two rotors, side-by-side, churning the water and causing it to flow up the ouside of the box, and down the center of the box. At the bottom of the box are small agitators, making sure the water in the uptake gets sufficiently churned.

This setup causes a steady flow of water to pour downward through the middle of the box. Now imagine a knife suspended there, with some kind of guard on the spine. The guard is designed so there is a constant laminar flow along the edge of the knife.

If the water is charged with a powdered abrasive, then after a sufficient length of time it should produce an even, symmetric wear pattern along the edge of the knife -- sharpening it. The agitators are present to ensure an even distribution of the abrasive; and the heavier the abrasive, the more quickly it wears the knife.

An advantage to this system is that the same water/abrasive could be used many times. And you could sharpen many knives at once, if the box were long enough. The major cost is the electricity to turn the rotors, and figuring out the exact length of time needed for each type of abrasive.

If the abrasive is very fine, it should produce an extremely acute edge, since in effect the knife will take on the shape of the water's laminar flow. Like a river wearing down a rock, I think a fine abrasive would wear the steel down to the most minimal edge possible.

Is this a foolproof, inexpensive way to sharpen large batches of knives at once?

Wondering,
JohnW
 
Thats a really interesting idea. I'd be skeptical as to how sharp they would get though. From my experience, water tends to round things out and make them smooth. I realize that the way you intend to guide the flow would change the geometry a little but I still think you'd end up with a very convexed edge.
Also, not sure how fast the abrasion would really occue. You've have to have the water moving really fst to get any kind of pressure from the abrasives. It can be done, look at a waterjet cutter, it just takes some pressure.
 
JohnW,

Have you been drinking? :D ;)

But, seriously, this could be a fun thread - I can see the potential already. :)

I like the idea of water being the vehicle for an abrasive. :D I would never dismiss someone's ideas outright, but you may have some homework to do. Here are some things I am GUESSING might give you some trouble:

I SUSPECT there would be a some kind of (turbulance?) problem where the water met at the edge, so I'm thinking you'd have to do one side at a time.

I also think gravity would not be enough - it would probably take 20 years to sharpen a knife this way using gravity and abrasive-filled water alone. So, you'd need to pressurize the water somehow.

I also suspect that a fine abrasive (because it's wet) would never actually touch the knife but there would always be at least a few molocules of water between the abrasive and the steel. I think you'd have to use something a little hard and heavy that would only be carried by pressurized water.

If I were motivated I'd look up some of these things, but HECK! YOU'RE the inventor! ;)
Good luck, man. I hope it turns into something for you. :)

[edit: Darn-it, Matt. I spent too long typing and you beat me to a few things!]
 
Fluid flowing past a suspended object develops what is called a stagnation point along (geneally) the lead edge of the object, where the flow divides around the object. There is also a pressure rise at this point. If we assume the knife is suspended edge up, as if "cutting" the flow, I think what would happen is the bevels would wear but so would the edge itself, so that the blade would never get sharp but round off as Matt suggested already. A very creative "out of the box" idea though.
 
After thinking it over a while, I think in principle the idea would work but would be very hard to build and control. One problem is focusing the erosion of the blade only where you want it. If the whole blade is in the flow, the whole blade wears, not good. I can propose maybe one way around this. Think of water flowing over a dam: the upper surface forms a smooth parabolic curve until the water eventually falls straight down. Now picture two parallel dams, with water from both falling in between them. Where the two curved surfaces meet, there would be (in cross section) a nice curved vee, something like a hollow grind shape. If you suspended the blade edge down, with just the edge bevels postioned in the vee, you could get the wear action concentrated just where you want. You could control the shape of the vee by varying the distance between the dams, or the flow rate, or both. The question then becomes: can you control all these variables accurately enough to get a consistant result? My guess is that it would be very difficult. And even if you could, I think it would take a very long time to put on an edge since there would be little pressure behind the abrasive. A lot of fun to think about, though!
 
Actually, there are devices that pressurize water, along with baking soda, or some other common substance, for the stripping of paint from motorcycle/bicycle frames. Could be it's used in custom auto painting as well. The method produces a finish that supposedly requires very little finish sanding prior to priming and painting. I heard about this 10-15 years ago, and I don't know if the technique took off or not.

As far as just plain water, without high pressure, I'm not sure what the result would be on knife edges. I think it would round out the edge.

Most knife edges need microscopic serrations to allow them to cut. Perfectly smooth edges might have some advantage in specialized applications, but I'm not sure about real world applications.

It is an interesting theory though. I wonder about the time factor as well.

Thomas
 
You are thinking in the right direction as far as using water as a suspension medium for abrasives.

Vapor honing sounds similar to what you are thinking of. I do not know much about it yet, but rumor has it that this technique is used on the blades of disposable razors.

An example:
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=5,709,587.WKU.&OS=PN/5,709,587&RS=PN/5,709,587

Also, WaterJet Cutting works on the same principle.
 
You must log in or register to reply here.
Back
Top