Machining graphite is horrendous. I spent many a hour removing graphite dust from motors and electrical gear caused by operators not using extraction equipment after machining electrodes for spark erosion. The last thing I would use is graphite it gets everywhere and is abrasive and a good conductor of electricity.

David

Amorphous carbon might be abrasive, but graphite is used as a lubricant (think graphite chain grease? )

, so cannot be an abrasive hazard!

Motor brushes (don't wear very quickly) are often of quite soft graphite (DC brushes rather than AC).

We use graphite marvers when forming glass beads, so it is available. Not cheap, mind.

I doubt there is going to be a great loss of energy whichever recommended material option you take, for this application.

Noggin End sell small amounts of graphite.

SA660 is bearing bronze which would be the one to look for. Or LG2 if you want to get that from Noggin too

I work for a specialist graphite machining company. so see the stuff (in various grades – and there are many, with widely differing properties) being machine daily. Most grades are easy enough to machine with normal metalworking tools – HSS, carbide inserts etc. For short run special profiles, form tools made from silver steel & gauge plate used unhardened also work. It is abrasive to the tools – a bit like cast iron. It is also very dirty, but (according to HSE investigations conducted at my employer's previous company), poses no particular health hazards and, in particular, poses no explosion risk as airborn dust as it requires the continous application of heat to cause it to burn. Motor brushes are mainly carbon IIRC, not graphite (we don't make motor brushes).

If you PM me the dimensions of the billet you require, I will see if I can get you a suitable piece of fine grained Isostatic graphite from the oddments bin. My employer is usually OK with this & only requires that photos or videoes of the finished item / machine are sent so he has the option of using them for publicity purposes. This grade machines to a good finish & parts can be made to close tolerances (we hold sizes to better than 0.01mm) – it is a bit dirty, mind !

Nigel B

The graphite we machine is man made from, as I understand it, a mixture of coke and pitch. The coke is ground to specific grain sizes according to the grade of graphite required. Other compounds may also be added, like iron filings or sulphur to vary the properties. The resultant thick paste is either extruded or isostatically pressed into blanks, then baked to form a carbon block. The carbon blocks are stacked, covered in deep layer of coke, then heated to very high temperture by passing an electric current through the stack – this converts the carbon to graphite. Improperly graphitised blocks have a higher resistance & are harder to machine & I understand that the graphitisation process is "one chance" process – if it is not done properly first time around it can't be re-visited..

The properties of the blocks vary depending on the mix & how it is processed – some are soft enough to be able to take chunks out with a teaspoon, while others are almost like ceramic & can only be worked with diamond tools – with many variations in between. My understanding is that these man made graphites are different to the natural deposits that are used for graphite lubricating powders – but my understanding may be flawed. When we are asked to supply graphite powders, these come from different suppliers & are physically different to the talc-fine dust that comes out of our dust extractors from machining extruded & isostatic blocks.

Nigel B

Hi PaulR,

Last year NigelB was good enough to send me some graphite, from which I have machined some bearings for Stirling Engine. Unfortunately, I have not made any further progress with it yet due to health problems for both me and my wife. It's a bit messy to machine, but if you cover the oily bits of your lathe, it cleans up easily with a vacuum cleaner.

Hello,

I have had some graphite which was in my materials cupboard for many years. I had reason to use it a year or two back. Yes it was very messy, but machined very well indeed (super finishes). So my experience says go for it! The only snag is that I don't know what grade it was. I was told it was pure graphite whatever that means.

Andrew.

I made a graphite piston for my sterling engine. To avoid some of the mess i taped the vacuum cleaner hose to the toolpost. As per soem advice here I polished the end result with plain copy paper. It was from whatever quality of graphite rod it was that was for sale on ebay. It drilled easily and held a tapped thread. I'd guess that for an accurate small hole one might pilot drill then make up a simple pin reamer (three flats to a point)