Don't bother using the pressure washer. A better way to look at waterjet power is in terms of Horsepower. Even the smaller machines are rated at 25HP and above. Pressure washers simply don't have that kind of power.
Not saying your wrong or anythin but you said do not look at pressure washer but look at horsepower. So what about this (http://www.northerntool.com/webapp/w...21&R=200317421) I do not have the money for that but still its some where around 25Hp, 7HP less but still. Remember i am not trying to cut aluminum and steel and carbon fiber, i am going to cut stuff like soft woods, foam, and plastic. So if that is rated at 18HP then i can use a pressure washer correct? And as some other people said thier pressure washers puts dents in concreate and stuff.
The problem is that pressure washers and flowjets are two completely different animals. Pressure washers are looking to generate just enough force at the work surface to lightly abrade it, and remove contaminants. A flowjet is punching clean through. Flowjet is high pressure/ low volume; pressure washer is high volume/ (comparatively) low pressure. 100W CO2 laser/ vs. 100W light bulb. Both deliver the same amount of energy, but in completely different ways. Now, you WILL be able to blast your way through things like soft wood, etc. with a powerful enough pressure washer, but to what end? The quality and speed of the result will not justify the cost.
If you are looking to work fairly soft materials, and want speed, your best bet is a high speed spindle. If you want something exotic, look into a good CO2 laser. Thin materials are quickly cut, and the cost of laser systems has been steadily decreasing- you can get a decent turnkey CO2 cutting laser head starting at about $7500 these days. Look at the Synrad 25W system that Torchmate offers. It would probably be sufficient for your application.
Even a 4000 psi pressure washer is not enough to cut something. Pressure washers will erode concrete and wood but it is not cutting it is the water being forced into small defects in the surface and prying it away.
Water jet cutting is dependent on the speed of the jet and it is just not fast enough to cut until you get up into the 25,000 psi region or higher.
Perhaps this analogy might help: You are probably familiar with the nylon filament grass trimmers that "cut" grass. Well they don't really cut it in the sense that a knife cuts it is more a case that the nylon thread hits the blade of grass so fast that it shears a piece of grass out at the point of impact. To do this the filament has to be travelling fast, something like 5000 to 7000 fpm. At lowers speeds the grass bends around the filament and the filament flexes but "cutting" does not take place. There is a critical speed region; below this the filament and grass all tangle up while well above it the filament shears through the grass as if it had a razor edge. Water jet cutting is similar; below the critical pressure region you will get erosion of brittle, defect filled material like concrete or wood which has soft spots and well above the water has enough speed, and kinetic energy, it more or less punches material out of the way. Even the highest psi pressure washer is well below the cutting pressure.
Lasers are cheaper and less dangerous. But really, I'm curious why you wouldn't go with a router. It often pays to start with easier projects and work up. You'll be the only person in your neighborhood with one, that's obvious.
They all need a motion system, it's just the cutting mechanism is much easier with the router, much more difficult with the laser, and an orders of magnitude more difficult with the water jet.
I think you will need to do some experimenting to satisfy your curiosity.
With such a low pressure I think you will cut MDF but make it go soggy. Real wood will proberbly deflect the cut to follow the grain.
While you will cut your foam, the cost of building a machine could leave you with something that you are dissapointed with at the end. Remember that with the lower pressure you will get a lot of water splashing about so you will have to ensure everything is waterproof. A high pressure Supersonic jet will not splash, just cut.
All right thanks everyone i guess i won't do a diy waterjet. But yeah i am going to do a router though i want at least 4 axis (a rotary table) so i could do a little wood work. I just thought it would be a cool idea of having a cnc waterjet o well. I would get a laser but i thought they were dangerous because without the proper ventelation it causes cancer and i could not have as much axis on a laser or could i?
Im curious as to why you want a waterjet cutter? you mention cutting softer materials, wood, foam, plastic. there are so many easier ways to accomplish this. On your limited budget (not that we all arent) Id start with something like a small dremel powered router and master the whole cnc thing, electronics, software etc. then move on to whatever it is you need to build to accomplish your task. Another thing is, when i was younger i used to use a very powerful pressure washer, maybe 3500 psi and approx 3 gallons per minute WITH a sandblasting attachment, so i had the combination of pretty high pressure and sharp abrasive and even with that i could sort of WEAR a hole in wood or cement. Nothing even close to a useable cut. I wish you well, but hope you dont waste too much money on this idea.
I agrea I would not suggest a DIY water jet Pump just from the exspearance I have with ours we use well over 40,000 psi to cut parts out. And it will cut would with an abrasive (Garnet) but so slow I could out run it with a hand saw. The wood traps the abrasive in it and the fresh abrasive strikes the trapped abrasive and brakes it down.
I would rather cut metal with the waterjet than wood. But as a note it will cut most anything given enough time.
Water jets are also made with constant line pressure in mind. The water is pumped through high pressure line .04-.06 i.d. Then it hits an orfice as small as .013 dia. I think you would destroy a pressure washer very fast as it would just work too hard trying to push the water through such a small space.
I wanted to build a diy waterjet because i thought it would be different and something fun to do but now that i see the serious price for this kind of stuff and the danger involved i am just going to build a 3 axis cnc router and continue upgrading that 3 axis maybe up to 6 axis. Plus now that i look at it why make a waterjet that will cost more then a cnc router and be able to cut less. It does not make any sense so i am just going to build a cnc router with a moving gantry instead of a moving table and probable around 3 Feet by 3 Feet. But thanks everyone for the info anyway, now i know that a diy waterjet can not be done on a budet.
I think you can run into problems trying to cut wood with a DIY waterjet. I can punch a hole through 0.5 mm thick of most metals easily using a micro sandplaster with 100 micron aluminum oxide at 80psi. But, if the metal was protected by a thin, soft wax coating (.2mm) then the force of the abrasion particles is aborpted. I think, you can run into the same problem with an underpowered waterjet. Another problem you might have is that wood absorpts water. It then expands and twists.
If you are looking for a nozzle for an experiment, you may want to look into micro sandplasting tips made Renfert.