4 ms·

What's the advantage of water vs metal blades? Do metal blades not cut through glass/porcelain/etc well?

by weberc2 10y ago

mcphage 10y ago
In addition to what others said, inside holes are a lot easier.
Terr_ 10y ago
IANAWaterJetGuy, but I think a big draw is that (A) you can make arbitrary cuts and very turns and (B) less risk of shattering brittle substances.
mey 10y ago
https://en.wikipedia.org/wiki/Water_jet_cutter#Benefits https://en.wikipedia.org/wiki/Water_jet_cutter#Benefits
clarry 10y ago
Waterjet & laser have cut through a small point that can follow any programmed 2D path and can start a hole in the middle of a sheet. By contrast blades are often very restricted as far as shapes go. Imagine cutting a disk with a band saw. A wire saw can get closer, but you don't start a hole with one, and AIUI it's quite slow (a thin wire is fragile, you can't feed hard). Milling tools can likewise follow arbitrary paths but usually the tools are unnecessarily large for cutting a shape out of a sheet. So you have higher forces and need better clamping and waste more material. Tiny milling tools exist but again you run into issues with fragility & low feeds, high rpm requirements, coolant, tool wear, etc. And the depth of cut tends to be very limited. All of the said methods will leave burrs instead of a nice smooth cut. The setup for laser cutting can be very very simple.
- weberc2 10y ago
  I was indeed picturing a mill setup. I guess the cost of the abrasive seems higher than the costs associated with material loss, coolant, etc at the hobbyist scale, but I'm also not particularly familiar with this domain.
  - chromaton 10y ago
    The waterjet is especially flexible compared to a milling machine. The small kerf means you can create smaller features. There's no need to change tools depending on the material type. Chips are automatically blasted into the catch tank, instead of accumulating on the workpiece. Waterjets also typically have a much larger workbed compared to a milling machine, so you can load an entire 4x8 foot sheet and cut a bunch of different parts, or one big part. I think you're right, though. For occasional prototype parts you're probably better off either ordering waterjet cut parts from an online service, or running them in a small CNC milling machine.
  - clarry 10y ago
    Well, if waterjet works anything like laser (we had a big one at work), then you just barely need to clamp the work. Gravity does its part, and I imagine the cutting force would be aligned with gravity, pushing the work into the table. So the setup really is simple and easy, and you can cut parts off the sheet and let them just drop. By contrast, milling tools will try to push the work in all directions depending on what kind of cuts you're taking at the moment. They will also try to pull the work (and if the work is loose, you can easily shatter tools). Of course the countering forces affect the tool and through it the rest of the machine, which needs to be rigid enough to take it. The workpiece and the part that will fall off must be clamped accordingly, and then you run into the issue of tool paths that would cross over your clamps, so you'll need the operator to re-clamp things in the middle of the job. And there are clearance issues when you try to operate small tools near clamps. It's definitely harder to set up, and more involving than a laser that just needs a path and then cuts it all up for you after you press play. I don't know what exactly the state of the art of hobbyist scale machine tooling is right now, but I would be surprised if high speed (=> suitable for small tools and low forces) CNC mills were commonly available. Most hobbyist machines I've seen are neither rigid nor CNC, so you won't be easily cutting smooth & complicated shapes with them.
    - DannyBee 10y ago
      "Well, if waterjet works anything like laser (we had a big one at work), then you just barely need to clamp the work. Gravity does its part, and I imagine the cutting force would be aligned with gravity, pushing the work into the table. So the setup really is simple and easy, and you can cut parts off the sheet and let them just drop. " Go hit part of something not flat to within a few microns with 75k psi of water and see if it vibrates :) Also, unless your nozzle alignment is perfectly vertical, there is some sideways motion imparted. (IE you are kinda right, but you still gotta do something) Particularly for small pieces, it can be a pain in the ass. On the plus side, yeah, light clamping with c-clamps/etc works most of the time.
knodi123 10y ago
for fun comparison, check out EDM (https://en.wikipedia.org/wiki/Electrical_discharge_machining https://en.wikipedia.org/wiki/Electrical_discharge_machining). Now THOSE guys can cut metal precisely.
crispyambulance 10y ago
I would like to know how its possible to operate this thing without wearing down the nozzle as fast as you're cutting the workpiece. Is the grit fed down the center of a laminar flow of water so it never touches the metal of the nozzle?
- semi-extrinsic 10y ago
  The particles in the flow won't hit the nozzle much at all, since the average flow is tangential to the nozzle walls. Even if the flow is highly turbulent inside the nozzle, there is a boundary layer where the velocity becomes zero. However, when the flow impacts a solid object, the particles can't "keep up" with the fluid splashing away due to their inertia, so they hit the solid object at high speed. Particles in turbulent flow are characterised by (among others) the Stokes number [1], which says something about how well the particles follow the flow. This depends e.g. on the particle size, roughness, and the density difference between solid and fluid. I imagine they have tuned the Stokes number to an optimal tradeoff between cutting speed and nozzle/fluid line wear. [1] https://en.wikipedia.org/wiki/Stokes_number https://en.wikipedia.org/wiki/Stokes_number
- Cerium 10y ago
  The nozzles do wear and are made of hard but brittle materials. Bumping the nozzle when joging the machine around is an easy 200 USD mistake to make.
- chromaton 10y ago
  The waterjet "jewel" is typically diamond, and the nozzle tungsten carbide. Both are very hard, and thus wear slowly. Though they do wear.
chromaton 10y ago
Waterjet has a small kerf, typically 0.04 inches, or 1 mm. It can go even smaller with specialized setups (microjet). The waterjet cutting stream automatically cools the material as it cuts, leaving heat treatment intact. Waterjets can also cut through material that would too hard to machine with ordinary metal tools, like hardened tool steel, stone, etc. I have some more information on the Big Blue Saw website: https://www.bigbluesaw.com/faqs/parts/how-does-waterjet-cutting-work.html https://www.bigbluesaw.com/faqs/parts/how-does-waterjet-cutt...

What's the advantage of water vs metal blades? Do metal blades not cut through glass/porcelain/etc well?

by weberc2 10y ago

What's the advantage of water vs metal blades? Do metal blades not cut through glass/porcelain/etc well?

mcphage 10y ago

In addition to what others said, inside holes are a lot easier.

Terr_ 10y ago

IANAWaterJetGuy, but I think a big draw is that (A) you can make arbitrary cuts and very turns and (B) less risk of shattering brittle substances.

mey 10y ago

https://en.wikipedia.org/wiki/Water_jet_cutter#Benefits https://en.wikipedia.org/wiki/Water_jet_cutter#Benefits

clarry 10y ago

Waterjet & laser have cut through a small point that can follow any programmed 2D path and can start a hole in the middle of a sheet. By contrast blades are often very restricted as far as shapes go. Imagine cutting a disk with a band saw. A wire saw can get closer, but you don't start a hole with one, and AIUI it's quite slow (a thin wire is fragile, you can't feed hard). Milling tools can likewise follow arbitrary paths but usually the tools are unnecessarily large for cutting a shape out of a sheet. So you have higher forces and need better clamping and waste more material. Tiny milling tools exist but again you run into issues with fragility & low feeds, high rpm requirements, coolant, tool wear, etc. And the depth of cut tends to be very limited. All of the said methods will leave burrs instead of a nice smooth cut. The setup for laser cutting can be very very simple.

weberc2 10y ago
I was indeed picturing a mill setup. I guess the cost of the abrasive seems higher than the costs associated with material loss, coolant, etc at the hobbyist scale, but I'm also not particularly familiar with this domain.
- chromaton 10y ago
  The waterjet is especially flexible compared to a milling machine. The small kerf means you can create smaller features. There's no need to change tools depending on the material type. Chips are automatically blasted into the catch tank, instead of accumulating on the workpiece. Waterjets also typically have a much larger workbed compared to a milling machine, so you can load an entire 4x8 foot sheet and cut a bunch of different parts, or one big part. I think you're right, though. For occasional prototype parts you're probably better off either ordering waterjet cut parts from an online service, or running them in a small CNC milling machine.
- clarry 10y ago
  Well, if waterjet works anything like laser (we had a big one at work), then you just barely need to clamp the work. Gravity does its part, and I imagine the cutting force would be aligned with gravity, pushing the work into the table. So the setup really is simple and easy, and you can cut parts off the sheet and let them just drop. By contrast, milling tools will try to push the work in all directions depending on what kind of cuts you're taking at the moment. They will also try to pull the work (and if the work is loose, you can easily shatter tools). Of course the countering forces affect the tool and through it the rest of the machine, which needs to be rigid enough to take it. The workpiece and the part that will fall off must be clamped accordingly, and then you run into the issue of tool paths that would cross over your clamps, so you'll need the operator to re-clamp things in the middle of the job. And there are clearance issues when you try to operate small tools near clamps. It's definitely harder to set up, and more involving than a laser that just needs a path and then cuts it all up for you after you press play. I don't know what exactly the state of the art of hobbyist scale machine tooling is right now, but I would be surprised if high speed (=> suitable for small tools and low forces) CNC mills were commonly available. Most hobbyist machines I've seen are neither rigid nor CNC, so you won't be easily cutting smooth & complicated shapes with them.
  - DannyBee 10y ago
    "Well, if waterjet works anything like laser (we had a big one at work), then you just barely need to clamp the work. Gravity does its part, and I imagine the cutting force would be aligned with gravity, pushing the work into the table. So the setup really is simple and easy, and you can cut parts off the sheet and let them just drop. " Go hit part of something not flat to within a few microns with 75k psi of water and see if it vibrates :) Also, unless your nozzle alignment is perfectly vertical, there is some sideways motion imparted. (IE you are kinda right, but you still gotta do something) Particularly for small pieces, it can be a pain in the ass. On the plus side, yeah, light clamping with c-clamps/etc works most of the time.

knodi123 10y ago

for fun comparison, check out EDM (https://en.wikipedia.org/wiki/Electrical_discharge_machining https://en.wikipedia.org/wiki/Electrical_discharge_machining). Now THOSE guys can cut metal precisely.

crispyambulance 10y ago

I would like to know how its possible to operate this thing without wearing down the nozzle as fast as you're cutting the workpiece. Is the grit fed down the center of a laminar flow of water so it never touches the metal of the nozzle?

semi-extrinsic 10y ago
The particles in the flow won't hit the nozzle much at all, since the average flow is tangential to the nozzle walls. Even if the flow is highly turbulent inside the nozzle, there is a boundary layer where the velocity becomes zero. However, when the flow impacts a solid object, the particles can't "keep up" with the fluid splashing away due to their inertia, so they hit the solid object at high speed. Particles in turbulent flow are characterised by (among others) the Stokes number [1], which says something about how well the particles follow the flow. This depends e.g. on the particle size, roughness, and the density difference between solid and fluid. I imagine they have tuned the Stokes number to an optimal tradeoff between cutting speed and nozzle/fluid line wear. [1] https://en.wikipedia.org/wiki/Stokes_number https://en.wikipedia.org/wiki/Stokes_number
Cerium 10y ago
The nozzles do wear and are made of hard but brittle materials. Bumping the nozzle when joging the machine around is an easy 200 USD mistake to make.
chromaton 10y ago
The waterjet "jewel" is typically diamond, and the nozzle tungsten carbide. Both are very hard, and thus wear slowly. Though they do wear.

chromaton 10y ago

Waterjet has a small kerf, typically 0.04 inches, or 1 mm. It can go even smaller with specialized setups (microjet). The waterjet cutting stream automatically cools the material as it cuts, leaving heat treatment intact. Waterjets can also cut through material that would too hard to machine with ordinary metal tools, like hardened tool steel, stone, etc. I have some more information on the Big Blue Saw website: https://www.bigbluesaw.com/faqs/parts/how-does-waterjet-cutting-work.html https://www.bigbluesaw.com/faqs/parts/how-does-waterjet-cutt...