Water jet cutter

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Herbiev

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I am toying with the idea of making a water jet cutter. Is it possible to build a 6000psi piston driven by a cam. Can anyone steer me in the direction of plans ?
 

Scott_M

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Hi Herbie

Here is a very good resource. "Waterjet University" And 6000 psi is a bit light for cutting metal most are 20-30,000 psi.

And here is a "feed rate calculator" That will give you an idea what pressure will do what.

That should give you some stuff to study. I looked into this a few years back and bailed on the idea.

Scott
 

Herbiev

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Thanks Scott. Looks like some interesting reading.
 

Entropy455

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Water alone will only make light cuts. Add an abrasive powder however, and you can make fast cuts on thick material. Unfortunately these types of abrasive-assisted waterjet tables are cost-prohibitive for a hobbyist. The cheapest one I've found was 40 grand - used, and it was at the end of its life (requiring expensive overhaul $$$).

Note that the upper threshold for pump pressure on a waterjet table is set by the Mach number of the system fluid - in this case water.

Said another way, if the water velocity through the nozzle ever hits Mach (about 4871 feet per second at 70 degrees F for water), you will have shock-events within the nozzle, and quite literally blow the nozzle apart. This is why abrasive powders are introduced - because there's an upper limit for usable cutting pressures.
 
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Herbiev

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I intend to use 80 grit garnet via a hopper into the water jet
 

Tim1974

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There good machines but be careful I’ve seen them go bang lol
 

salzburg

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There is quite a bit on youtube about DIY waterjets.
Also google the 'WAZER', on preorder for less than 5.000.
 

MachineTom

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The issue is the power needed to effectively cut material equal or better than the various saws available. There are two methods to generate high pressure water, volume of water is very low less than a gallon per minute.
6000 psi will cut wood, I saw a Utube that had a a guy using a pressure was pump at 4000psi and with garnet cut thin AL.
To build a motor driven pump that can handle 40K-60K psi will be $$$. and need a 40-60hp motor to drive it.
Second method is an intensifier pump. its a hydraulic pump/motor, driving a large hyd cylinder, this is directly connected to smaller diameter water filled cylinder. Say the area of the hydraulic cylinder is 10 square inches, and the smaller cylinder for water is 1 square inch, that ratio is 10 : 1 which would increase the pressure available from 3000 in the big cylinder, would be 30, 000 psi in the smaller water cylinder but the volume would be 0.100 the volume output of the pump.

I any case you need big HP to get the pressure needed. As a standard you need 1hp, to pump 1 gpm at 1000 psi. So you needed 5 hp to pump 5 gpm at 1000 psi, or 1 gpm at 5000 psi.

The Hydraulic method is somewhat easier, as you can find used HP cylinders around, that can lower the cost but nowhere near the cost of using a plasma cutter or saw.
 

Mike Henry

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The garnet cost and disposal could be an issue, too. I believe that the garnet is single-use, the lb/min is fairly high, and the spent garnet might be considered haz waste, depending on local laws and what you are cutting. The Wazer folks have published some material consumption data so that might be one source of data so you can do your own cost calcs.
 

Entropy455

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1 gpm at 1,000 psi requires 0.583 horsepower, assuming a 100% efficient pump. An 80% efficient pump would require 0.833 horsepower for the same pressure & volumetric rate. The 1 horsepower rule is a bit conservative, but might be more accurate when all system losses are included.

3 gpm at 90,000 psi will require 197 horsepower of pumping power, assuming an 80% efficient pump. The largest table I've seen will cut parts from 12" thick stainless plate. As mike mentioned above, the abrasive is a one-shot use. Note that there is absolutely nothing cheap about waterjet tables. What they can do however is pretty awesome - comparable to EDMs.
 

Ken I

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Most high end waterjet machines use a "dynamic head" which allows the head to tilt to compensate for the tendency of the kerf to fan out which would otherwise leave you with a slight angle on your cuts.
You can even cut a countersunk hole with these machines.
Garnet powder is inert and can generally be disposed of in landfill sites - it is after all just another form of sand. But it will also be contaminated with whatever you cut with it and that might be a problem.
The pump barrels have a typical life of 2000-5000hrs before they fatigue crack.
My local waterjet supplier has me hooked and I now design with this in mind - its cheaper than wire cut EDM and only slightly more costly than laser and the thickness cutting ability is phenomenal.
I've even had gears waterjet cut (increasing the clearance and root radius to adapt to the 1.2mm kerf) - works an absolute charm for M2 and up.
Keep us posted - Regards, Ken
 

Mike Henry

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Ken - can you provide an estimate of the operating cost to cut, say, a 1 foot length of any metal that you work with? Just curious....
 

Scott_M

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In post number 2 I linked to a feed rate calculator that also estimates "running" costs.
I had considered building one but the power requirements were to high to justify. There is a shop nearby that is very fair on price. I just use him now and don't have to worry about maintaining another machine and keeping it busy.
Scott
 

Ken I

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Mike - I don't actually do waterjet cutting myself and I would go along with Scott_M's comments.

Another nice feature of WJC is you can cut (relatively) small holes in thick plate - with laser you are limited to hole diameters about the same as plate thickness.

Looking at my last quote from my "local" (in South African Rand - which had another bad day - trading at 3.141 to the Swahili Gumbo Bead)
I had 5.63ft cut in 30mm thick mild steel with 16 piercings for R2113.42 = ±U$24.80 / ft
I had 2.68ft of 20mm thick mild steel with 3 piercings for R325.48 = ±U$8.20 / ft
Clearly thickness and number of piercings have an influence - contact your local shop - they all appear to use costing algorithms - but I've never asked.

Also the % speed of cut is a parameter - typically 40, 60, 80 & 100% speeds are available - higher speeds are cheaper but the finish is worse.

The above costs were at 60% which is pretty fine - comparable to a fine sand-blasted finish. I only use 40% for things like gears.

Re this radius gauge I posted under downloads - almost entirely waterjet cut.

https://www.homemodelenginemachinist.com/threads/radius-gauge.30239/

Hope this helps.

Regards, Ken
 
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Mike Henry

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In post number 2 I linked to a feed rate calculator that also estimates "running" costs.
I had considered building one but the power requirements were to high to justify. There is a shop nearby that is very fair on price. I just use him now and don't have to worry about maintaining another machine and keeping it busy.
Scott
Thanks Scott - I'd missed that on my 1st read.
 

Mike Henry

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Mike - I don't actually do waterjet cutting myself and I would go along with Scott_M's comments.

Looking at my last quote from my "local" ...

Re this radius gauge I posted under downloads - almost entirely waterjet cut.

https://www.homemodelenginemachinist.com/threads/radius-gauge.30239/

Hope this helps.

Regards, Ken
Thanks for those $/foot numbers - they mesh with what I was thinking.

Nice job on that radius gauge, btw. That gadget would have been useful for a few past jobs.
 

Herbiev

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Thanks for all the suggestions. As I have a plasma cutter I might just CNC that machine.
 

MachineTom

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Said another way, if the water velocity through the nozzle ever hits Mach (about 4871 feet per second at 70 degrees F for water), you will have shock-events within the nozzle, and quite literally blow the nozzle apart. This is why abrasive powders are introduced - because there's an upper limit for usable cutting pressures.
Could you expand on the Mach issue. Is not the mach of air 1125fps, so would not the mach of air be the bar, rather than the mach of water?
The noise in a Waterjet shop is from the big ass motor, and then the roar of the cutting head. Granted it has been 20 years since I was last in a WJ shop.
 

ssaxer

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There was an article in MAKE magazine ( I do not remeber the issue off hand but enclosed a scan of the article) where a guy used an off the shelf gas pressure washer to make a unit. We had a group of student here at the university I work for also make one (they did a poor job of executing). Look carefully at the WAZER unit, last time I looked they had pushed off shipping any units and were now over a year behind (projected ship date according to the web site is March 2019).. Price went up over $2000 from their projected price during their kickstart campaign.
 

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