CNC Waterjet

[hook'em]

Foamcutter, I used to program for and operate one, I also trained other operators. And because our company was small, I also got to do the maintenance/upkeep on it too. So I'll give you my 'gist', of how the 'pump' works from first hand knowledge. Unlike common house hold pressure washers which boost only the water itself, the WJ I worked on (FLOW model 9X Waterknife 52k Max psi) used a very large, 3ph, 220V motor to drive a hydraulic oil pump. This in turn drove a double ended piston setup ( reciprocating motion)( being pushed by oil pressure and pushing water as well), which has a multiplying effect on the water (20:1 if I remember right) so 2000 psi oil pressure would get you 40k water psi. Having seen the internals, not really sure this is something you want to pursue as a home project. Pistons and cylinders are extrememly close tolerance and highly polished materials, with plenty of low and high pressure seals to keep everything where it sould be. Just for reference, I will try to post a crude sketch of the intensifier pump.

As for the abrasive, we used an 80 mesh (size) ruby garnet mixed in to the flow of water just before the end of the cutting tube, right after the orifice( the jewel you spoke of which focuses the water). It was a simple barrel hopper that used a micrometer controlled opening to allow the garnet to be gravity fed into the water stream via a vinyl tube attched to the cutting head. The flow of water created a natural siphon effect, but was aided by 10-15 psi of compressed air.

[foamcutter]

hook'em,
Thanks for the info. Your right I don't think I want to build the pump. I am thinking buying used pump, building the rest except buying a "jewel" and mixing tube for abrasive to build a nozzel around. It looks to me like other than those three parts not too tough of a DIY project. But those three challenges will need to be resolved first before anything else is attempted since without them there is no waterjet. All of the rails and moving parts would need to be inside bellows to protect them from the spray. Just thinking out loud Ron

[doug6949]

Foamcutter;

I can't remember if you were involved in the waterjet discussions on diycnc or mach2 so I apologize if I'm repeating myself.

The current technology is 55-60ksi and this is out of the question for homebrew. 20ksi intensifiers are old tech now and should be available as surplus. For granite engraving/cutting this is adequate. All wj consumables are available off the shelf.

Pressure washer pumps are available up to 10ksi and 5ksi is common. You can do engraving at 5ksi. Glen Howells on the yahoo waterjets list can steer you toward the details.

Doug

[foamcutter]

Doug,
Thanks for the info. I will post a email on yahoo waterjets. I joined but haven't posted yet since I was still checking out the info there. I was not involved in any other discussion on waterjets so any links or info you are willing to share will be much appreciated. Thanks Ron

[doug6949]

The waterjets group is for commercial interests and some members can be abrasive toward DIY types. However, there is some good information to be gathered there by reading.

I will be more than happy to answer questions so fire away.

Doug

[doug6949]

Sorry, part of the above post was cut off. Here it is:

I never have any luck searching yahoo so I can't provide tags to the threads. If your luck is better you could try searching DIY-CNC and mach1mach2cnc.

Doug

[foamcutter]

Doug,
I am planning to start out with cutting and carving, engraving in soft stone like soapstone and Alabaster then work my way up to marble and then granite. What size of cutting kerf is realistic? On the engraving I want to be able to do small intricate designs and lettering, is this going to be possible? What is the smallest practical "jewel" orfice size? I think I should be able to cut and engrave soft stone with water only but will need abrasive when I start working on the harder stone, am I correct in that assumption? I am also thinking I should be able to do good work with a pressure at 20K psi on about a 20hp pump and less, even when I go to hard stone. Can you point me to some places that might have used pumps for a reasonable investment? Also any sources for the nozzel parts. That's all I will ask this time, I really appreciate your help. Ron

[doug6949]

Ron;
20Ksi is not only adequate for stone, it is recommended over higher pressures in many cases. 55Ksi tends to shatter glass, stone and ceramics during the pierce. Flow has a low pressure pierce function for this reason.

The jewel orifice is typically around .013" and produces a .022 kerf using abrasive. Softer stone can probably be cut without abrasive. This is good because garnet is the single biggest expense of running a WJ.

Newer pumps are mostly direct acting whereas to older style is hydraulic intensifier. Direct acting is cheaper to rebuild but doesn't go as long between rebuilds. It's a wash. Intensifier systems are much more expensive new but probably a better bargain on the used market. People are getting away from them because of the complexity.

20hp is probably adequate for a 20Ksi pump. Several posts have been submitted to the waterjets group requesting sources for parts and used pumps. The answers follow them. If you post such a request you should get current information as well as a few offers. All the consumables and repair parts are available as aftermarket stuff. I don't have specific sources as I am not currently working on the WJ equipment.

Doug