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My brother designed and built his own plasma cutter. I wonder how useful people would find that?
by chris_wot 7y ago
My brother designed and built his own plasma cutter. I wonder how useful people would find that?
- pstuart 7y agoI'm sure it would at least be interesting to the HN crowd. Any link to info on it?
- jacquesm 7y agoI should dig up the data on mine and write it up.
- kragen 7y agoA 120-watt laser like the one in the Lasersaur can maybe cut 6-mm MDF at 50 mm/sec. A typical plasma cutter can maybe cut 6-mm mild steel at 50 mm/sec. https://www.makeitfrom.com/compare/ASTM-A36-SS400-S275-Structural-Carbon-Steel/Medium-Density-Fiberboard-MDF https://www.makeitfrom.com/compare/ASTM-A36-SS400-S275-Struc... suggests that A36 mild steel is 25 times as rigid and 25 times as strong as MDF.† So I think that in some sense a plasma cutter is about 25 times as useful as a low-power laser cutter like this one. Of course, there are a multitude of other properties to consider. Mild steel fails through ductile deformation; MDF fails through brittle fracture. Mild steel rusts when it gets wet; MDF swells and loses most of its strength. Steel weighs 8 g/cc, and MDF weighs 0.75 g/cc. (That means that if you can make the steel thin enough, you can get the same tensile strength as MDF with 60% less weight using steel. You might even be able to cut the steel with a laser cutter, though probably a higher-power one.) Steel is cold to sit on and not breathable like MDF. MDF won't cut your fingers if you don't deburr it. Lasersaur claims precision of 30–100 μm, and even 100 μm is hard to reach with plasma cutting. Steel rings because its elasticity is almost perfect, with a Q over 1000, while MDF thuds because it has a lot of elastic hysteresis, so it eats vibration for breakfast; by the same token, though, it is not suitable for high-precision positioning. Lasersaur can cut some transparent materials, while a plasma cutter can only cut metals. And plasma torches are kind of dangerous but far less treacherous than a 100-watt laser. But, at the crudest, most oversimplified level, you can build things just as fast and 25 times as skookum with a plasma CNC table, or several times as fast and just as skookum, or equally skookum and much lighter. And a lot of the same design principles carry over, although plasma torches have more trouble with sharp corners than laser cutters do, because they can't ramp their power down to zero. † According to that site, A36 has a Young's modulus of 190 GPa and an ultimate tensile strength of 480 MPa, though you probably don't really want to exceed its yield stress of 290 MPa. MDF has a Young's modulus of 4 GPa (no word on whether that's in-plane or transverse) and a tensile strength of 18 MPa.
- mlyle 7y agoI'm not sure why one would ever consider mechanical properties of MDF when one could cut plywood, etc. The appeal of a laser cutter is you can cut things with no hold-down, engrave in the same pass, and get nice finished edges on acrylic or wood, including sharp corners and very small intricate details. I have a milling machine, a plasma cutter, a CO2 laser, and 3D printers (and some other stuff). The laser cutter can't be used for everything, but for the stuff it can do I prefer it over any other tool. It's just easy and good.
- kragen 7y agoMDF laser-cuts a lot more predictably than plywood, and it's cheaper. I agree that laser cutters are super awesome. I wouldn't want to try to cut plywood or acrylic with a plasma cutter!
- justinclift 7y ago> I wouldn't want to try to cut plywood or acrylic with a plasma cutter! In theory (!) plasma cutters require the material being cut to be conductive.
- kragen 7y agoYeah, I've seen people trying tricks with sheet metal on top, but...
- mlyle 7y agoFiberboard certainly looks prettier, but I cut plywood all day long.
- kragen 7y agoWhat kind of tolerances do you get on your plywood cuts? Lasersaur is claiming they get down to 30μm on some materials. I'd think plywood would be more like 200μm, from what I've read, but I don't have any real experiences.