Re: Water Jet

Just a couple of thoughts on water jet projects...(BTW, I have never used
one of these)...

High pressure is definitely non-trivial.

Once you get over a hundred or so psi, you can no longer use common
hardware. Injection injuries become possible since a concentrated fluid
jet penetrates the skin quite readily. Leaks anywhere in the system cut
just as effectively as at the nozzle.

Airless paint pumps operate up to 3,000 psi, as do pressure washers.
Probably won't cut more than paper, plastic, and people.

Once you exceed a couple of thousand psi, there are no readily available
hardware items.

Once you get over 10,000 psi, sealing anything is tough. You are also
entering the pressure ranges of firearm chambers and barrels. Probably the
only practical way to generate these pressures without spending megabucks
is with an air amplifier - an air cyinder directly driving a hydraulic
cylinder with differing piston diameters. For example, a 10 square inch
air cylinder driving a 0.1 square inch hydraulic cylinder would "amplify"
the air pressure by a factor of 100. So 100 psi into the air cylinder
would produce a hydraulic pressure of 10,000 psi. The nozzle could be
mounted on the end of the hydraulic cylinder. This would be small and
compact. It would also be a slow, intermittent cutting process - the
equivalent of chain drilling. But maybe feasible for DIY.

It won't be cheap. Air amplifiers are available commercially that go to at
least 50,000 psi, but the flow volume is extremely low, and they cost
several $1,000. My old McMaster Carr catalog shows a 10,000 psi air driven
hydrostatic test rig for $2000 and a high pressure hose for 36,000 psi (the
highest pressure they offered) working pressure at $200 for a 5 foot
length, with fittings. And NOT pipe thread fittings!

Other than mechanical abrasion and chemical corrosion, there probably won't
be much difference between the action of any common fluid. Water has the
very desirable benefits of no fire or toxicity hazard, and low viscosity.

Nozzles - if you expect the nozzle to last longer than the piece being cut,
it will have to be HARD. Carbide orifice plates with small, straight holes
should be available at reasonable cost.


Steve - who has enough trouble cutting metal with HSS.