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Comment by danielmorozoff | Hacker News Reader

How does this compare to a co2 pump laser CNC? what conditions would water jet be preferable especially because it also requires high power consumption? Co2 lasers are cheap and pretty easy to build/ maintain. They also can put out enough power to cut steel. In my experience only special optical/thermal materials like borosilicate glass or certain plastics are not good with co2 because of heat build up/ stress and fracturing properties

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CO2 lasers aren't great for many metals due to wavelength issues. Waterjets create essentially no heat affected zone. As an example, I've cut two inch thick black granite with a waterjet, and I'm not sure a CO2 laser would do more than scuff it. Silver seems to just reflect infrared lasers like a mirror. Some plastics make nasty fumes in a laser, but cut fine with water. When both technologies were in their earlier years, I would have taken a waterjet over a laser for most industrial uses. Now I think I'd lean more towards a fiber laser. I'm not sure how much more innovation there is left in the waterjet realm, but lasers seem to be continuing to get better.

Thanks that makes sense.

What cut edge quality can waterjet achieve? It seems it would be a factor of the abrasive material particulate size. Has pure waterjet been employed (the pressure requirements would be huge I would assume but doable). I've seen directed explosive blasts + water cut through cars :)

https://www.youtube.com/watch?v=gHJo956BtJM

It's interesting you bring up silver/ other IR reflective materials), as I know fiber lasers cut silver.

Here's a cool paper on it:

http://onlinelibrary.wiley.com/store/10.1002/latj.201390001/....

I actually worked on beta testing what was, around eight years ago, the most precise waterjet in production. It did indeed use very fine sand that seemed to get into everything. Keeping it from caking was the main challenge. Edge quality on an OMAX is a software setting (I love their software and use it for everything 2D and vector). Basically, the numbered quality settings allow you to prioritize what kind of edge quality you want. 1 gets you the bare minimum needed to get the parts to separate. 2 is fine, but a bit rough on the bottom. Picture that the waterjet pierces the material and then moves slowly, grinding the interior edge of the cut along the path. If you corner quickly, it flares out in the opposite direction. I think of it as being like cutting with a paintbrush. 3 is optimized for dimensional accuracy on the top of the cut. Despite the fact that the water stream spreads out as it goes, the top of the cut is wider than the bottom. This is due to ejecta cutting on the way back out of the cut, and the velocity being higher near the nozzle. Higher numbers are for reducing the taper of the cut, but generally reduce dimensional accuracy. There are also settings for cutting without abrasive, which are generally only worthwhile for something soft or edible, and settings for etching, which I found too loud and messy to mess with. There are also nozzles that will tilt as they cut, which allows you to move and corner quickly by countering the taper with tilt.

I do have experience with cutting precious metals with a laser. CO2 and fiber lasers may both be infrared, but it's a big spectrum. CO2 is a wavelength better suited for cutting organics, and doesn't have the fine focus or energy density available in fiber. I've used a 70 watt picosecond fiber laser for cutting silver and it actually cuts very nicely, but the problem is getting up to the initial threshold to affect it at all. Titanium, with it's low reflectance to infrared, low thermal conductivity, and high melting point, will cut with a power setting that won't leave a visible mark on silver with its opposite set of properties.

That was an awesome description. Thank you

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