Live data from Hacker News

My Tungsten Cube (2019)

thume.ca

231–240 of 336 posts

Re: My Tungsten Cube (2019)

#231
post #217

Earlier quoted context omitted.

Hmm, I thought ECM and tap-disintegrating EDM (which is not very precise and does use a huge amount of power, unlike, say, wire EDM) had pretty astonishingly huge MRRs? I think the density ratio for tungsten and steel (19:8, just over 2:1) is actually more even than the atomic mass ratio (23:7, just over 3:1). So I'd think that even on a volume-per-coulomb basis ECM would cut tungsten faster, assuming comparable fara…

No, but if I had a machine like that here I'd definitely give that a work out because this is an interesting question that I normally would not have considered. That's a question worth settling, from memory the speed is not so much a function of the material as it is of the current density that you can achieve with the gear you have. Thousands of Amps will get you some pretty good speeds, on the order of a cubic cm o…

I don't really understand what the limiting factors on ECM speed are. There's electrolyte heating, cathode heating, bulk electrolyte resistance, formation of salt boundary layers on both the cathode and the anode, and so on. But one thing I do know is that MRR is proportional to the area of the interelectrode process gap: twice the area gives you twice the MRR at the same current density, whether the current density bottleneck is in the cathode, the anode, or the bulk electrolyte between them.

Electrolytic processes are really interesting and complicated, and 200+ years after Davy used them to revolutionize chemistry, I think they're still underused. I'm preetty sure you can produce Fresnel reflectors for a given wavelength, for example, by anodizing aluminum foil to about a quarter-wavelength depth, and across a wide range of visible wavelengths by anodizing it to about 3 microns depth, with the electropolishing effect inherently eliminating the small asperities that make it so slow to produce lenses and mirrors by grinding.

Plasma cutting should work, but should be slower on W than on iron; WP says that at room temperature its specific heat is 24.27 J/mol/K, but at 183.84 g/mol, that's only 0.13 J/g/K. For iron the same figures are 25.10 J/mol/K and 55.845 g/mol, so 0.45 J/g/K. So tungsten should heat up three times as fast with the same power output at room temperature; but tungsten's heat of fusion is four times higher, and I think that's actually the dominant component of plasma-cutting energy consumption. But I think you have roughly four orders of magnitude more knowledge about plasma cutting than I do.

Re: My Tungsten Cube (2019)

#232

Earlier quoted context omitted.

I had to look this up. It seems he has a periodic table with lots of little cubbyholes with pictures and items representing the element, but not every element is actually there. It's hard to find a good source for details about this display, but he has cubbyholes for all of the lanthanides and actinides, so there must be some that don't have the actual element being represented.

Yeah, I imagine that it'd be hard to get ahold of some technetium or astatine

Francium is the one I always think about. My understanding is the only source is as a decay product (probably from uranium) and that there's somewhere on the order of one ounce of it in the entire planet at any given time.

Not only that, but it's only true francium if it comes from France.

Re: My Tungsten Cube (2019)

#233

Earlier quoted context omitted.

If your finger is broken it will swell up so fast you may not even be able to get to the ring with something that can crack it. This is not something that I would risk for any price.

Just confirmed with my wife (ER doctor) that there is no situation where an EMT amputates your finger because they can’t get a ring off.

I don't think I ever said that an EMT would amputate your finger. I said that you might get further injuries. For instance: embedded Tungsten fragments or in case of a prolonged problem removing the ring further tissue damage.

Re: My Tungsten Cube (2019)

#234
post #204

We use blocks like this in our electron beam welders to set the beam power, shape and focus on older machines (newer machines use a CPU/DSP controlled system). A small 25x25x50mm block sits on an adjustable height stand which is set to the height of the weld joint. You dial in the settings, hit the block with the beam and using the optics, visually check the focus and alignment. Then you move to the weld joint and st…

> Tungsten is the only metal you can reliably use as our machines have beam powers up to 15kW which can precisely deliver an enormous amount of heat into a pencil point sized area. Even at the common 1-3kW ranges the tungsten instantly liquefies when the beam turns on. I'm sorry - is there an error here? As I understand the rest of your comment, you use Tungsten because it does not liquify?

The whole block doesn't instantly liquify like other metals, just the small point the laser hit (hence the small dent after).

Re: My Tungsten Cube (2019)

#235
post #208
post #142

Earlier quoted context omitted.

My choice was titanium, which I used to make ours. It is (IMHO) among the finest of all materials for the job.

> among the finest of all materials for the job. Titanium should also work great for forced amputation in the case of a broken finger I suppose...

What is with the anti-ring cartel on this thread?

Every metal mentioned has someone talking about losing a finger. Do you work for a silicone ring company?

Re: My Tungsten Cube (2019)

#236

Earlier quoted context omitted.

It's not like that money disappears. Just think of it like buying gold bullion. Unlike say, a $9000 motorcycle impulse purchase, a block of raw metal should hold it's inflation adjusted value relatively well for decades and you can sell it whenever to recoup the money.

Gold bullion has a healthy market to sell back into though.I don't know the numbers, but i wouldn't be surprised if I could easily sell gold for 80% of "market" value, whereas probably closer to 20% for something like Iridium that has a very small adressable market unless I were to expend considerable effort finding someone willing to pay what it's worth.

Iridium is commonly used in jewelry; it's one of the platinum group metals.

It doesn't have the mass awareness of gold, but it's not some weird niche material either.

Re: My Tungsten Cube (2019)

#237
post #231

Earlier quoted context omitted.

No, but if I had a machine like that here I'd definitely give that a work out because this is an interesting question that I normally would not have considered. That's a question worth settling, from memory the speed is not so much a function of the material as it is of the current density that you can achieve with the gear you have. Thousands of Amps will get you some pretty good speeds, on the order of a cubic cm o…

I don't really understand what the limiting factors on ECM speed are. There's electrolyte heating, cathode heating, bulk electrolyte resistance, formation of salt boundary layers on both the cathode and the anode, and so on. But one thing I do know is that MRR is proportional to the area of the interelectrode process gap: twice the area gives you twice the MRR at the same current density, whether the current density…

That Fresnel reflector idea sounds super interesting.

Has anybody tried that?

Re: My Tungsten Cube (2019)

#238
post #163

Earlier quoted context omitted.

Osmium would be heavier still (22.59 grams/cc), and a relative bargain at $1275 for the 10mm cube at the same source. Not polished/shiny though.

And, as divbzero's Quora link points out, it's going to kill you by oxidizing into a toxin when exposed to open air.

That seems to be a concern with osmium powder, ground osmium, etc. I don't think that a cube has any handling requirements more exotic than lead solder.

Re: My Tungsten Cube (2019)

#240
post #208

Earlier quoted context omitted.

> among the finest of all materials for the job. Titanium should also work great for forced amputation in the case of a broken finger I suppose...

What is with the anti-ring cartel on this thread? Every metal mentioned has someone talking about losing a finger. Do you work for a silicone ring company?

It's a real hazard that is well known in the trades, but might not be appreciated by people who are attracted to the idea of an exotic metal ring but are not in situations where they will be warned about it. The warnings here seem reasonable to me.
Post reply on HN