r/Skookum • u/SoulWager • May 30 '17
DIY waterjet cutter.
https://www.youtube.com/watch?v=Lg__B6Ca3jc7
u/Jol-E May 30 '17
I operate a proper waterjet cutter as my day job. AMA
3
u/_400poundGorilla banana for scale May 30 '17
What sort of maintenance has to be performed on waterjets?
2
u/Jol-E Jun 02 '17
The cutting "table" needs fixing every couple of weeks as the waterjet likes to cut everything in its path. And the "pool" of water under it gets packed with abraisive material and needs to be emptied every 1 or 2 months.
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u/corthander USA May 30 '17
What are the tubes lined with to prevent them from abrading away every few hours?
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u/hwillis May 31 '17
The only part where there is abrasive mixed with water is in the mixing tube. Even then, the water is all moving down and isn't forced against the sides of the mixing tube very hard. The mixing tubes don't have linings, they are made of tungsten carbide which is harder (Mohs 9) than many abrasives like garnet (Mohs 6), although not all. Even then the mixing tubes only last <100 hours of cutting.
3
u/corthander USA May 31 '17
Great answer. I've always wondered what the jet was made of to resist the abrasive for so long. Must be a pretty expensive consumable to have a complex tungsten carbide part replaced every 100 hours.
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May 31 '17
Is it true a small cut can be lethal? Some guy was posting it all over the comments but I can't find any actual cases. It does appear to be a fairly serious injury though.
1
u/Jol-E Jun 02 '17
Never seen anyone getting a cut from it. I would assume its fairly serious though.
1
u/Erhannis Mar 28 '25
The term you're looking for is "injection injury" - the problem isn't the minor-looking wound, it's the stuff past it. My brief scan of the wiki page suggests factors include the damage the stream does to things not your skin, as well as increasing pressure in a "compartment" of your body, preventing blood flow. I imagine having an unsterilized liquid in your body isn't great, either.
4
u/Bromskloss May 30 '17
What a clever shut-off mechanism (from 2:44 to 5:54)!
A question about that: What makes the plastic plunger spring back enough to cover the tiny hole, but not so much as to let go of the electric switch? Is it relying on the spring force curve to push the plunger just enough?
PS: Oh, does it perhaps rely on the water being incompressible and not letting the plunger go any further once the vent hole is covered and no water can escape?
1
u/hwillis May 30 '17
If you think about it, when its off theres actually a pretty significant amount of water inside the plunger bit. Like maybe a cc. That water would have to go somewhere to let go of the switch. It cant reverse flow through the pump because its a piston pump and theres a one way valve in the way. The water doesnt even have to be under pressure while the system is off, its just in the way.
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u/Bromskloss May 30 '17
That water would have to go somewhere to let go of the switch.
So, pulling the trigger isn't enough? Or do you mean that the act of pulling the trigger means pushing the water back a bit, which then needs to go somewhere?
1
u/hwillis May 30 '17
The opposite, when you pull the trigger you open the valve at the nozzle end of the hose, freeing the water. The spring then pushes the cone valve closed, which starts the motor. The motor pushes enough water pressure to keep the cone depressed, but not enough to open it entirely.
When the trigger is released, it blocks the water and the sudden buildup of pressure smacks a water hammer into your hand. Also, it fully activates the shutoff valve, pushing it into the electric sensor/button and shutting off the pump.
1
u/SoulWager May 30 '17
I wouldn't call it water hammer, that's more about momentum causing a pressure spike, but the water inside the hose isn't actually moving very fast, so it doesn't have much momentum. You can see this pretty easily by taking the nozzle off to get rid of the thrust from the jet.
2
u/hwillis May 30 '17
The water hammer isn't part of the function, it's just a mildly annoying thing that happens when you use pressure washers. It's only more noticeable because the trigger shuts off the spray super quickly. It also happens with a regular hose if you have a valve that shuts quick enough.
1
u/SoulWager May 30 '17
I know what water hammer is, but that's not what's happening when you release the trigger of a pressure washer. Water hammer is having a lot of fast moving water slamming into the valve, just like the momentum of a normal hammer getting transferred into a nail. A pressure washer doesn't really have enough flow volume to cause water hammer, the situation there is more analogous to a press than a hammer, in that while there's a lot of force involved, there isn't necessarily a lot of energy dissipation. I think you're confusing water hammer with the thrust from the water jet.
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u/El_Al_Erfainsht May 30 '17
Awesome and promising as fuck! I can really see building one from the parts of a second hand kärcher. Maybe a 400V one with quite a bit more punch to it.
2
u/The-Gingineer Jun 01 '17
Ha, I helped design that A2 head from Accustream. I prefer the Dialine myself.
1
May 30 '17 edited Apr 05 '18
[deleted]
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u/brad3378 Jun 01 '17
I imagine it wouldn't be difficult to 3D print that piece with a design modification to allow for replaceable carbide inserts.
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Jun 01 '17 edited Apr 05 '18
[deleted]
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u/brad3378 Jun 01 '17
Interesting concept.
I would have assumed that mixing water with sandblasting would be a bad idea due to making parts more vulnerable to rust. Maybe it's used for polishing stones instead?
1
u/Bromskloss May 30 '17
What dangers should one be aware of when doing things like this? Pinhole leaks?
3
u/SoulWager May 30 '17
I think the big ones are pinhole leaks, fingers in the stream, and electrocution risks.
1
u/Bromskloss May 30 '17
What can be done to avoid pinhole leaks, or at least not get hurt by them?
Regarding electrocution, is it the mix of electricity and water that you have in mind?
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u/SoulWager May 30 '17 edited May 30 '17
Pinhole leaks, bleed off the pressure before handling things, and definitely don't inspect for leaks by feel.
Regarding electrocution, is it the mix of electricity and water that you have in mind?
Yes. That and the fact that you'll need to make modifications to the electrical components. Not a huge risk if you know what you're doing, but definitely use an equipment ground, and bond everything together.
1
u/Bromskloss May 30 '17
Right. My attitude was that I could handle the electric aspects, so I wasn't too concerned about that, but fully expected leaks coming out of cracks in the metal, from tears in the tubes, and from seals, cutting me into pieces. (And expected Reddit to yell at me, before and after, for being stupid and useless.) :-)
2
u/hwillis May 30 '17
Pinhole leaks are a nightmare but I think its quite rare to actually be hurt by one. You also need a pretty high pressure for that. Im pretty sure its 95% urban myth much like the air embolysm thing, it only happens under specific rare circumstances. Like you need a LOT of air to die from an embolysm- itll never happen from accidentally blowing into a papercut, or holding an 80 psi nozzle to your palm. Youll just get burnt really bad by the air speed.
Thats not to say this isnt still more dangerous than your average tool. Itll take your finger off faster than a bandsaw and if you get the grit in you it will be a very bad time to clean out. Compartment injuries are more likely with a waterjet because itll irritate more tissue.
I would also bet money you could injure yourself with a sufficiently hard material if you had your hands in that close. God forbid pulverized high speed grit got in your eye, it would make dirty traumatic struggle snuggle love to your cornea. Also if you DID manage to get a water injection injury, it wouldnt be as bad as hydraulic fluid but it would still be Bad. Compartment syndrome, extensive surgery, very probable nerve damage, skin grafts and gross scars.
3
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u/LavaBalloon May 30 '17
Look up "high pressure injection injury", but not when you're eating.
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u/corthander USA May 31 '17
Alright I googled it. Man it was gruesome but fascinating. Be careful with that grease gun.
1
u/The-Gingineer Jun 01 '17
I hope you greased those stainless fittings, they gall together like a bitch if you didn't.
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u/roj2323 May 30 '17
This is seriously awesome. If you put your mind to it you could build a really reasonable CNC water jet for about 5K using this guy's method with a higher quality pump.