Machining Graphite

A custom-sized pencil sharpener?

(Sorry, couldn't resist....)

I don't know if metals are out of the picture, but maybe the same technology for making tungsten GTAW electrodes might offer some potential.

ha ha, thanks for the vote of miniaturism. (Don't forget Ed Weldon's trick of using a drill as a mini-lathe)

anyway the stocks I am looking at are called "fine extruded" rod or "isomolded" sheet. Just thought somebody who has worked em might give me a few tips.

I know carbide tools are recommended. But that's all I'm getting from google.

On "Myth busters" they made rocket nozzels from graphite rod using a lathe and what looked like off the shelf tooling.

oilcan13

Googling "graphite rods" gives lots of stuff on fishing poles, but "graphite rod stock" might help:

http://www.google.com/search?sourceid=ie7&q=graphite+rod+stock&rls=com.microsoft:en-us:IE-SearchBox&ie=UTF-8&oe=UTF-8&rlz=1I7ACEW_enUS408US408

Well, you were right that the search terms weren't quite right... this morning I tried "carving graphite" instead, and found lots of info from people who use it for glass molds.

apparently it's as easy as sharpening a pencil... but a filthy mess. Wet saw recommended.

I think you need to disclose the "desired qualities" as I have no idea as to the goals in this.

E.g. is this a 'consumable', or electrode support, or 1 of 20 possible reasons for machining graphite, say as in spark erosion?

Or does "Dremel" mean maybe we are in casting? If so, of what?

All would effect the advice applicable, as the graphite employed is different.

This is for silversmithing. So the dremel part, I'm thinking of carving out some shallow relief on a piece of graphite sheet.

The graphite stock I was looking at is used for crucibles, mandrels etc.

I was about to suggest looking at http://www.zircarceramics.com/ and their moldable and castable refractory products. But, if you are casting fine scale silver then their material might not be appropriate.

If you don't mind posting it, who is the manufacturer of the graphite stock that you are considering using?

Thanks,

Bruce

Thanks for the link, Bruce. As a matter of fact, I have been looking into the high temp ceramics as well. Interesting product at Aremco. They make these Pyro Paint refractory coatings as well as a potting compound that looks promising for fine detail molds, Ceramacast 575N.

I am considering a possible supplier of the graphite stock; http://www.weaverind.com/ recommended by glass artists for their custom graphite machining.

Be sure to have adequate exhaust/ventikation unless you really LIKE having black lung disease.

I cannot offer direct help here but I do remember one of our machinists at work shaping a large block of graphite (many inches) on a lathe for some experiment. I remember that the block was turning fairly slowly (~30rpm). He was marking a cutting line with a white pen at the time. (When I see unusual things at work I like to find out what's going on. These guys normally fabricate things out of metals and the occasional block of silicon.) He said that with how brittle graphite was he had to take only small parts off at each cut. He also said that he was grateful that graphite was relatively cheap as he pointed to a small pile of broken blocks. When I left the room I heard the lathe speed up followed by a simultaneous crunch and expletive. The next day I saw the machinist and asked him how that project was doing. He said that he finished and the requested three machined pieces of graphite were done but it sure made a mess of the shop.

Good luck.

GA. I didn't find any useful comments about brittleness in my research this morning, but the mess is something everyone agrees on.

In fact, check out the cautionary tales and advice at the bottom of this page. It's one thing to make a mess, another story to put your machinery in jeopardy because of the dust.

I've pretty well decided at this point, to get a few simple mandrels machined for me, and get a small graphite sheet to try out as a work surface (graphite, carbon, charcoal make it easy to reach working temperatures, cw firebrick and other surfaces that absorb heat). As for the mold carving idea, it looks like graphite is not the best choice...

Come to think of it, since that graphite machining day the ancient hand me down lathe and milling machine that were in the room have been replaced with much newer machinery. The only two machines still in place from that day are a grinder and band saw that were on the other side of the room. Maybe that's just a coincidence, maybe the graphite dust did those machine in, or maybe the dust damage is why they accepted the graphite milling job on the old machines in the first place.

If it's a lathe job, you really need a very vibration free tool post grinder - not a normal cutting tip.

To Artsmith;

Why not use a wax positive and plaster?

The mess is not just during machining. We had some jigs made from graphite once but gave up using them because of the mess just from handling them.

Thanks for the heads up.. I will make sure to discuss this with the machinist. I have a graphite stirring rod and there's no dust from handling it at all. It's a very hard stock and, obviously, whatever dustiness is generated in manufacture they get rid of it so the product is dust free. That's what I'll be asking for, for sure!

Here's some numbers to chew on and remember DO NOT inhale the dust!

Machining graphite electrodes effectively demands a fast spindle, a fast control . . . and dust collection. Requirements like these make it easy to see why graphite electrode milling is one of the few jobs that has machining centers designed specifically for it.

Micropulse's graphite machining center was supplied by Bostomatic (formerly Boston Digital; Milford, Massachusetts). The machine features a 30,000 rpm spindle and a CNC-based compensation system that maintains accuracy by adjusting for thermal effects.

Typical programmed parameters for finish milling used to be 3,500 rpm and 30 ipm. Finish cuts now are run at 35,000 rpm and 400 ipm.

on the older machines, the difference between choosing a step-over of 0.005 inch and one of 0.003 inch

Check the lnk below.

http://www.substech.com/dokuwiki/doku.php?id=machining_graphite_and_carbon&DokuWiki=a38a6fa606d5ca585200be2f407b5873#general_guidelines_for_machining_graphite_and_carbon

Graphite is easily machined using conventional tools, milling, turning, or grinding. It is brittle and tends to be chippy, so some care is needed. Always cut into the work rather than cutting off to an edge. It is also rather abrasive so grade C3 carbide is recommended if you are going to do a lot of cutting. Graphite grinds very well with a vitrified alumina wheel. But it is dirty, a good dust collector or vacuum cleaner is an absolute necessity. The most important factor is to use a good grade of graphite. I recommend an EDM grade such as Poco EDM 3

I used to machine graphite all the time for our EDM machine. It is easy machining and you can use coolant on it with no ill effect to keep the dust down. There are many different grades as well. I was more familiar with copper impregnated graphite. CNC machining will obviously be your best bet for fine intricate details but it can be successfully done on manual machines as well. If you use a Dremel, you won't want to use coolant so use a vacuum with a fine dust filter.

It's an interesting point that the degree of difficulty and brittleness may depend on the grade of the graphite. The dust issues seem to apply to all.

Sadly dust management is not my strong point. Since I don't have a good vacuum setup, it looks like I won't get to play with the graphite this time around. Rats!

Try looking in the "Machinist Handbook" There may be a table for cutting graphite, also tooling manufactures like Valenite and Kenametal have free engineering help available on the web and by phone.

Contact Morganite, they will do mall batch specials.