The questions about knives here reminded me of something I’ve been wondering about.
What is the backing for those water knives? Those uber-pressure water jets that they use for machining and cutting metal. I had always assumed the water jet was stationary, and fired through a hole into a tank of water, to have the force absorbed or something. But I was watching an American Chopper episode where they used one. The metal was stationary and the jet moved. What do they use on the backside? I can’t figure out what would stop a water jet designed to cut hardened steel, without quickly becoming eroded and cut and worthless and it doesn’t seem feasible to calculate the exact cutting pressure needed for the material with that much precision everytime.
Are you sure you aren’t thinking of a drill with a lubricating stream? If you’re talking about the rims they did on the firefighter bike, that’s what it is.
Good question and one I’ve often wondered about.
Its not just a water lubed drill/blade. Its using water itself, or water with cutting particles, to do the actual cutting. They use this technique for, among other applications, marble and stone cutting. An example is marble countertops.
The jet of water is extremely high pressure, at the cutting point. But the pressure is significantly less just a foot beyond that. And several feet beyond, it is quite a bit lower pressure. So they basically have nothing backing it, except empty air, for several feet, until the pressure is low enough to be safe.
So-called water saws use a combination of an abrasive compound and very high presssure water. Extremely effective when the nozzle of the jet dispensing the water/abrasive is in very close proximity to the object to be cut. Not so effective at even slightly greater distances. Therefore, the object to be cut is often held only an inch or less away from the backing on a series of pins that do not intersect the area to be cut. In some applications, this is not even necessary because, when the saw is properly calibrated, the energy of the water/abrasive is expended entirely on the object to be cut.
There was once a tale in the magazine of the National Knife Collectors Assn. about a Water Cutting Knife. A man had mastered the art of making a blade so sharp it could separate a stream of water into hydrogen and oxygen. The poor guy was chased into hiding by energy companies. Some of them wanted to change the world, and some wanted to buy his secret and hide it away. Ah, well. It was just a story, right. Right? :eek:
If you’ve ever used a pressure washer you can see the same thing happen. When the nozzle is an inch away, the water jet can strip paint. A few feet away from nozzle, it’s harmless mist.
The actual backing is, on the water jet I used, just a grid. It was about 1/8" x 1" bar in about a 1"x 1" grid with the 1/8" edge facing up - supporting the material the water jet is cutting - yes it does cut into that backing a bit but it is not that bad and one may also put some scrap down to hold the work off the backing.
Now I used a “water knife” just last week but I do not believe you were talking about explosives.