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Comment by jcampbell1 | Hacker News Reader

As a person who made his own titanium wedding ring, I have to laugh a bit. It appears this ring is chamfered on only one side. That makes it a bit of a chinese finger trap, easy to put on, uncomfortable to remove. A good metaphor.

Don't tell my wife, but cutting a round chamfer on the back side of a ring is really hard. I built a custom chock and ground a tool to do just that.

Assuming the diamonds are all recessed, cutting a backside chamfer shouldn't be impossible. Just chock, indicate, and re-chock, repeat, until you get it aligned.

This is a brilliant piece of art.

The only thing I would add is that titanium is a PITA, but while I have no experience, apparently most of the problems go away when you have coolant. I have seen production cutting tools at GE Aircraft and they rough cut like it is butter.

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If you're familiar with stainless, Ti isn't that different. Go slow, listen to what your tools are telling you. Carbide tooling doesn't hurt, but isn't inherently requisite. Titanium is a wonderful jewelry material (biocompatible, low density, durable, polishes fairly well). It's only "downside" is that it's not expensive. Well-made Ti stuff draws the same attention as higher-Z materials.

I've made a number of Ti rings, but haven't set stones, as the You'll save a lot of time by starting with Ti tubing rather than turning the hole into chips. Depending on the size you need, relevant tubing isn't always available. Anodization is really fun.

I'd check into the biocompatibility of permalloy. Nickel allergies are real and can be acquired, sometimes from rings. Might rust/discolor fingers over the long term too.Laminating a Ti strip to the permalloy might help to attenuate the situation?

Chamfering the inside of a ring isn't hard to do with careful sanding on the lathe. Doing it wrong will amputate your finger or worse -- seek qualified instruction.

The article doesn't make mention of accommodating water/drainage. What happens if a little water gets beneath the stones after a hand-washing?

What a cool and inspired piece of work!

Somewhat offtopic, but since you mentioned anodizing titanium, it reminded me of an example - anodized titanium chopsticks:

http://tistix.com/cart3/index.php?main_page=index&cPath=...

> You'll save a lot of time by starting with Ti tubing rather than turning the hole into chips.

If we speak of finger rings it's not that much extra work, normally you can drill in with 12mm HSS bit even on a bench lathe. Solid stock also allows you to make eccentric rings.

I have a wedding ring without chamfering, I like the snug fit and the trick to getting it off is in relaxing your muscles and turning it as you pull it off. I paid special attention to this aspect as we were fitting rings since I heard this argument before. It seems like most 'modern' (i.e., square, boxy) design do not have a chamfer, and I didn't have problems getting any of them off (well aside from the too small ones, of course).

The alloy he used is essentially identical to that used for dental implants (Ti6Al4V ELI, where the ELI means very low purity limits on iron, C & O interstitials). Interesting that you bring up the coolant -- using tungsten carbide water cooled burs (bog standard dental stuff), this titanium alloy cuts very easily. By contrast, chrome cobalt (the stuff we make partial denture frameworks from), is harder than hell.

It seems that feeding and cuting speeds are quite different from aluminium or steel. Also if it overheats it's like if you heat treat it, it becomes almost impossible to cut. That's why you must use coolant if you want to have some good results.

It depends on alloy. Commercial grade pure titanium and grade 5 alloy (probably 90% of Ti stock out there) are easy to machine. Harder than aluminium, sure, but not anywhere close to hardened steel.

Titanium can be heat treated to an extent it doesn't gain that much. Also you really need a furnace for that kind of temperatures.

You need coolant if you use high cutting speeds, it also helps to remove swarf. It's still possible to machine titanium dry with appropriately formed cutter and get a fine surface.

(Source: I also turned two titanium rings)

Yes, the grandparent is probably misattributing annealing of the cutting tool to hardening of the Titanium. Titanium has a very high melting point and very low heat conductivity (for a metal). Using a hardened steel tool to cut Titanium too fast without sufficient cooling will heat up the tool hot enough to anneal the tool. It appears the Titanium has become harder, but in fact the steel tool has become less hard.

Note, I'm talking about cutting rates that you'll achieve by hand or by conventional CNC machine tools. At very high cutting rates, the chip (discarded metal) carries away significant amounts of heat, and in some cases increasing cutting rate actually reduces tool temperature and prolongs tool life. This was an active area of research in the late 1990s.

Yes annealing at the edge indeed can happen with HSS bits when ran dry.

The point about heavy cuts is interesting, although I'd be very uncomfortable without coolant - thin titanium swarf readily ignites in the air.

Any recommendations for getting a titanium ring enlarged? I can't imagine you could stretch the damn thing. Maybe I would need to find a shop to bore out the hole some more?

Yes, you need to machine out the inside a bit.

He had to cut a slot in it to stop inductive currents in the metal.

I would think that slot could be used for slight sizing adjustments.

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