Machining graphite?

[Cornish JackParticipant @cornishjack]

[Cornish JackParticipant @cornishjack]

G'day all.

One of my round 'tuits' is an own design hot air engine. In preparation, I bought some graphite rod. Haven't machined this stuff previously and would appreciate any advice re. the process. The rod diameter would, in fact, serve quite well, as is, for a piston or several and I'm wondering whether a better option would be to leave the graphite unmachined and bore the cylinders to suit?

Any thoughts or comments would be welcome.

TIA

Rgds

Bill

[NJHParticipant @njh]

Hi Bill

I've not turned graphite rod but I have milled a block to make a valve for a flame licker. It cuts beautifully and, with the end mill running fast ,a very smooth surface was produced. I see no reason why it should not turn well too. Sharp tool, light cut – obviously no coolant/ cutting fluid needed – the graphite is self lubricating. One word of warning – lay lots of paper around about – it makes an 'orrible mess.!

Regards

Norman

Edited By NJH on 11/09/2012 22:52:55

Edited By NJH on 11/09/2012 22:54:00

[Paul RusconiParticipant @paulrusconi80412]

Be sure to wear a face mask or use a good vacumm system when your machining carbon.

OHS issues with machining carbon

Carbon graphite dust can cause potential damage to your health. If the powder goes inside the respiratory tract, then irritation may be caused and symptoms like dyspnea, palpitation, tightness of chest and coughing may be manifested. On the other hand, chronic inhalation may lead to decreased pulmonary function, lung fibrosis, pneumoconiosis, bronchitis and black sputum. The graphite dust, if it goes into the gastro-intestinal tract, may lead to symptoms such as diarrhea, vomiting and a feeling of nausea. Carbon graphite dust can also enter the eyes, causing redness and slight irritation. If it comes into contact with the skin, graphite dust may cause mild irritation and reddening.

Read more: The Safety Hazards of Carbon Graphite Dust | eHow.com **LINK**

[NobbyParticipant @nobby]

Hi
I milled and turned electrodes for the sparking machines , another word of warning use a mask
nobby

[jason udallParticipant @jasonudall57142]

Further cautions.

dust extraction….needs EXCELLENT filtration before passing through motor comutator…( ask me how I know )…also though ('cos it conducts) not as bas a explosive haZad as say sawdust or coal or flour ..if using vaccum or air line ….BANG! ( think lots of surface area lots of air….)..

oilly "rag" seams best way to wipe up…also recomend barrier cream ….

in short nice to machine ( apart from work holding)… horror to clean up!

[Ian S CParticipant @iansc]

For those living in the USA (I don't think they send things out of the States), the manufacturers of the airpots with glass cylinders and graphite pistons sends out FREE samples, you just contact them on their web site ( a chap on another site has just got one), and they send it to you, just like that! Oh yes they will send the size you want. Ian S C

[Cornish JackParticipant @cornishjack]

Thank you, chaps, for most useful advice.

I particularly like John's newspaper 'filing' idea!! Just to follow that up, wouldn't the same caveat apply to the finished piston made thus, if the cylinder bore was in my usual 'badger's backside' finish?? I don't think I could improve on the 'as bought' finish on the rod which was why I thought that there might be some mileage in only having to generate an accurate bore – perhaps get some lapping practice in!!

Rgds

Bill

[Cornish JackParticipant @cornishjack]

John, thank you – beautifully explained, as ever. Point well taken and will go that route when I get started.

Rgds

Bill

[VersabossParticipant @versaboss]

Almost on topic question Jack: where did you buy that graphite, and in which diameter(s)? There are some sellers in the U.S., but postage is often much more than the material.

Greetings, Hansrudolf

[Ian S CParticipant @iansc]

Suggestions on other sites have been to check out foundries, they use it quite a bit, or foundry suppliers Ian S C

[Cornish JackParticipant @cornishjack]

Hansrudolph – bought both rod and block on Ebay but they were 'one-offs'. I found them with a google search for graphite rod but a subsequent search came up zilch!! The rod is about 10 – 12 cms long and approx 20mm diam and cost 6 GBP. The block is approx 800 x 800 x 40 mm and cost 16 GBP. Don't have any comparative prices to judge whether those are good or bad prices

Rgds

Bill

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

There are many grades of graphite and some are more suitable than others for engineering components .

Where possible use one of the compacted copper impregnated electrical grades as used for brushes on big electric motors .This is a super material – hard wearing , strong , easy to work and slippery .

Natural graphite is a rather poor material inclined to be flawed and to split bits off readily .

Graphite rod is available from scientific suppliers but an easier source would probably be to seek out some old brushes . Graphite in blocks is in any case rather easier to source than larger size round rods

Edited By MICHAEL WILLIAMS on 13/09/2012 18:03:29

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