Can crystals be tapped?

[ImanCarrot]

I got a problem looming on the horizon: I've made some little brass prototype components for a customer, but he's probably going to want a harder material for the production quantities.

Any ideas what to use? I was thinking Germanium or Silicon or something crystalline? but can this material be tapped? I need an M2 X 4mm hole in each and they are about 7mm long and 5mm in diameter.

Oh, and since I'm diamond turning them the material can't contain Carbon (so it can't be stainless steel for example).

Can anyone think of a metal or crystal which is harder than brass and machineable? (oh and not toxic, so Berylium's out).

*scrathes head* dontcha just love customers who design lovely stuff that looks perfect.... on paper.

Me: So what's the material then?
Customer: Erm.. we hadn't thought of that.. something hard?

*sheesh*

[Geof]

I was under the impression that crystals, lots of them and very tiny, were tapped all the time when metal is tapped. Unless of course you are working with some sexy rapidly cooled amorphous material.

[HuFlungDung]

Perhaps thread milling would be a more suitable process. If you have the facilities, you could even grind the thread in the same fashion as single point thread milling.

[ckirchen]

They just had an article in Haas's CNC Machining magazine (http://haascnc.com/CNCMag/PDF/v13i43.pdf, page22). The fellow is milling silicon nitride with a diamond tool and 200,000 rpm. I think thread milling/grinding is similar enough, so it should work.

[awerby]

I'm not sure what you're building, but it's a big jump to go from machining brass to machining some kind of crystaline mineral. I've never worked with germanium, but I have tried silicon, and it's not particularly durable, while being very difficult to machine. These materials also make abrasive dust, which will work itself into the sliding parts of your machine and degrade them.

So you're looking at trading a (relatively) simple machining operation for something more akin to lapidary work, which is completely different (and a lot slower and more difficult). Is your client going to be happy with the sudden increase in price along with decrease in production speed?

If these parts are even close to working in brass, I'd suggest you look into a tool steel. It's a lot harder, without getting you into a whole different mode of working which requires different machinery and methodology. You can anneal it and work with HSS tools, or work it hard with coated carbide tooling. I'm not sure why you'd want to use diamond tooling if you didn't have to, but maybe I'm missing something...

Andrew Werby
www.computersculpture.com

Originally Posted by ImanCarrot I got a problem looming on the horizon: I've made some little brass prototype components for a customer, but he's probably going to want a harder material for the production quantities. Any ideas what to use? I was thinking Germanium or Silicon or something crystalline? but can this material be tapped? I need an M2 X 4mm hole in each and they are about 7mm long and 5mm in diameter. Oh, and since I'm diamond turning them the material can't contain Carbon (so it can't be stainless steel for example). Can anyone think of a metal or crystal which is harder than brass and machineable? (oh and not toxic, so Berylium's out). *scrathes head* dontcha just love customers who design lovely stuff that looks perfect.... on paper. Me: So what's the material then? Customer: Erm.. we hadn't thought of that.. something hard? *sheesh*

[ImanCarrot]

Thanks all for the (as always!) good advice.

I'll put this on the back burner for now and propose machining trils on different materials.

[davereagan]

You can get stainless without any carbon if that matters. My experience with these PhD types who think little about availability is that they change their mind when you put a big cost number in front of them about how badly they need what they previously insisted on. Also, some of them never have the budget they imply. They like to play in the sand with your time.

[garagefela]

Originally Posted by ImanCarrot I got a problem looming on the horizon: I've made some little brass prototype components for a customer, but he's probably going to want a harder material for the production quantities. Any ideas what to use? I was thinking Germanium or Silicon or something crystalline? but can this material be tapped? I need an M2 X 4mm hole in each and they are about 7mm long and 5mm in diameter. Oh, and since I'm diamond turning them the material can't contain Carbon (so it can't be stainless steel for example). Can anyone think of a metal or crystal which is harder than brass and machineable? (oh and not toxic, so Berylium's out). *scrathes head* dontcha just love customers who design lovely stuff that looks perfect.... on paper. Me: So what's the material then? Customer: Erm.. we hadn't thought of that.. something hard? *sheesh*

At the risk of going off topic but why can't you turn something with carbon in it with a diamond. Ok a diamond is carbon just wondering what the problem is.

Inquiring minds want to know.

[ImanCarrot]

They like to play in the sand with your time

lol ain't that the truth. Unfortunately, they didn't seem to bothered about the cost and placed the order the very same day... a warning to us all on quoting high- if they say "ayup! ok" then you gotta make the dang thing hehe.

On the diamond thingy- what we find is the carbon graphitises the diamond and you get a bad finish (bad as in not opticaly perfect). I've diamond turned lots of stuff but some stuff just will not machine with a good finish no matter what the feeds and speeds etc.

I have to use monocrystalline gem quality diamonds and they got to be natural, none of this polycrystalline rubbish or synthetic stuff. They cost quite a bit, so it's a wee bit nerve wracking pressing that big green button.

[K&Y]

Originally Posted by garagefela At the risk of going off topic but why can't you turn something with carbon in it with a diamond. Ok a diamond is carbon just wondering what the problem is. Inquiring minds want to know.

Well, to make a long story short, it's referred to as "Thermo-Chemical Wear" of the diamond when machining ferrous metals.

"While diamond only softens at 1350 degree Celsius and melts at 3027 degree Celsius, and is also the hardest material in the world, it has a weakness. Diamond succumbs to graphitization, which means that it will change its crystal structure to graphite crystal structure at 200 degree Celsius in the presence of a catalyst metal such as carbon steel."

That being said, it doesn't mean that you cannot use diamond in order to turn stainless steel. It does however require a special process that is costly. Advances have been made on two separate fronts. Cryogenics and ultrasonic vibration have shown remarkable results in prolonging the overall diamond tool life and achieving an optical finish on stainless steel.


I hope that this answers your question.

[youngjim]

If you can't use stainless, what about one of the nickel or cobalt alloys? I'm sure they're as bad to machine as they are to weld (I have some peripheral experience to that bit of bother) but there may be a material in that class which is free of carbon.

Jim