machining graphite

[davidsutton]

I have been asked if it is possible to machine graphite - in order to make a mold for casting glass into - aparently the surface of the set cast glass clouds less if it is molded into graphite rather than plaster.
Does anybody have any idea what this involves - is graphite readily available? do people cut pure graphite or is it a compund - does it need cooling fluid, etc..
the question is just speculative so nobody please bust a gut... just finding out if anyone else has done anything similar.

[Andre' B]

Do some web searches for EDM electrodes, you will find graphite all over the place.
Just one example.
http://www.graphitestore.com/stores.asp/cat_id/12


You can use just carbide tools but there is tooling available just for graphite.

It basically turns to powder when you machine it, you will want to have a vacuum setup to keep down the dust.
That dust is very abrasive so you want to keep the machine as clean as possible.
No need for coolant but it does control the dust, the coolant then turns into a black mess the works great for lapping the machine ways and bearings. It will also soak into the graphite some and may affect the casting process.

Graphite comes in many grades, the more expensive stuff will give you a better finish.

[davidsutton]

thanks for the prompt reply, i checked out the link - graphite was less expensive than i thought it would be..
in terms of size though - do you think 5 inch x 5 inch x 3 inch block is obtainable - i only looked at the web link you suggested so far.. i have not done a wider web search yet

anyways thanks very much for your help
best regards
ds

[Andre' B]

That size is easy. The places that sell it to the end users get it in blocks the size of small cars and cut it up.

Just seen you are in the UK, I do know that EDM shops in Europe tend to use more copper for electrodes then we do in the US, but graphite should still be available.

[dang]

Does graphite need to be milled at high speeds?

[dang]

Apparently it doesn't need to be machined at high speeds. Feeds should, of course be proportional for best results.
The big issue as I understand it now is dust collection. The dust starts at the cutting tool and travels in the opposite direction of that tool. Vacuum solutions become more difficult as the part's complexity grows. The most modern and effective way to capture the dust is with coolant, not that you'd need that coolant for anything else.
Rather than quote the article, I'll just link to it.

http://findarticles.com/p/articles/m...67/ai_16339352

Like any good hall monitor would, I looked up disposal as well. The EPA and OSHA don't consider Graphite Dust to be dangerous so long as it's not floating around in the air or is caked to the workshop walls. I can't find any disposal regulations at all. Can anyone else find any rules or regs on this?

[DJPLAST]

Here is another source for graphite:
http://www.poco.com/Home/tabid/36/Default.aspx

[keithorr]

Graphite is just a material. It takes the thermal shock of molten glass but doesn't necessarily produce a good finish by itself. It conducts heat too efficiently to allow the glass to set without the surface seizing up; called chill marks.
I machine graphite for glass molds. Not many glassmakers understand how to use them. Sounds like a good idea but often is an exercise in futility.

You don't really want graphite;"graphite" is just a word people use. You want carbon which is the physical state before the billet is cooked to the graphite phase. It has to do with the thermal conductivity aspect.

GraphiteStore.com doesn't have the best quality material. I use some of their offerings for inexpensive substrates.

Ed Skeels
www.keithorrblowpipes.com/molds.htm

[dang]

I'm thinking of machining high density or graphite specifically for Aluminum and Zamak molds. I've seen some nice chemical additives that make release a snap and improve the castings finish.
I also read that I'll have to use Diamond End Mills to cut the Graphite. Does it machine easily, or is it very difficult? Please illuminate me further.

[K&Y]

Originally Posted by dang I'm thinking of machining high density or graphite specifically for Aluminum and Zamak molds. I've seen some nice chemical additives that make release a snap and improve the castings finish. I also read that I'll have to use Diamond End Mills to cut the Graphite. Does it machine easily, or is it very difficult? Please illuminate me further.

Your best bet as far as milling Graphite would be to use PCD (Polycrystalline Diamond) tipped endmills. They are widely used in the aerospace industry already.

[svenakela]

I was milling pretty much graphite before, EDM probes. We didn't use any special mills as I remember, just standard TIN-coated HSS-mills and sometimes carbide mills.

Either keep the milling process under water or use vacuum, you can't even imagine how dusty it is.

[K&Y]

Originally Posted by svenakela I was milling pretty much graphite before, EDM probes. We didn't use any special mills as I remember, just standard TIN-coated HSS-mills and sometimes carbide mills. Either keep the milling process under water or use vacuum, you can't even imagine how dusty it is.

You can use coated carbide, but if you were to run a head to head performance test on both variations, you'd see the difference. I'll use the following as an example:

PCD-tipped countersinks, and non PCD-tipped countersinks, used in the aerospace industry. You'll see somewhere in the neighborhood of a 200-300% increase in tool life for the PCD-tipped countersink. Large companies such as "POCO Graphite" use PCD-tipped tooling in their graphite production process, just to give you an example. If tool life isn't a concern, then it won't matter. As far as evacuating the dust, there are several solutions out on the market if you are going to be milling. You are correct when you say that it's hard to imagine just how dusty it can get when machining graphite.