On Sat, 9 Dec 2017 12:34:45 -0500, "Jim Wilkins"
wrote:

"Ed Huntress" wrote in message
.. .
On Sat, 9 Dec 2017 09:45:55 -0700, Bob La Londe
wrote:

On 12/9/2017 4:32 AM, Ed Huntress wrote:
On Fri, 8 Dec 2017 20:46:47 -0700, BobH
wrote:

On 12/08/2017 05:43 PM, Ed Huntress wrote:
On Fri, 8 Dec 2017 17:30:50 -0700, Bob La Londe

wrote:
If you haven't machined it, it's a piece of cake. Do you know
what
grade it is? Brand?

Most are very abrasive but you can go as fast as your spindle
will
allow. It machines more easily than magnesium. I machined a lot
of
thread-cutting electrodes from Poco 3 graphite a few decades ago
Easy-peasy. Don't be afraid of it.


Wicked messy though. Graphite dust everywhere. I bought some
equipment
from a shop that did a lot of graphite machining and it was a
dusty mess.

Despite the common understanding about graphite, the synthetic
variety, used in the applications we're describing, is very
abrasive.
It's coarse and gritty, rather than slippery flakes, which is the
typical structure of natural graphite.

I've been in shops that specialize in machining graphite EDM
electrodes and they replace machines every two or three years.
They
often buy Fadals for that reason: they're cheap, and nothing else
will
last longer, unless the machine is built for it.

I marketed Roku-Roku for a couple of years. They were pioneers in
building machining centers specifically made for machining
graphite.
They have a three-part approach to keeping graphite off the ways.

First, they have special way covers. Second, the area under the
covers
has pressurized air to keep graphite dust from entering. And
third,
they have a built-in high-volume vacuum system to suck the dust
out of
the complete machine enclosure.

As I said, I used to turn threading electrodes for an EDM company,
and
I'm serious about protecting the ways on my lathe. First, I don't
machine much graphite. Second, I cover the ways with oil-soaked
(WD-40-sprayed) newspaper, taped on tightly. Third, I cover areas
with
aluminum foil if I can't get newspaper around them. And fourth, I
make
a vacuusm plenum out of an old plastic milk bottle, attach a
vacuum
hose to it, and cut a hole in it that allows you to fit it closely
around the cutting tool and the workpiece.

If you're going to do much of it, you really have to protect your
machine. But machining it is really easy, requiring little force.
It
will wear HSS pretty quickly, however.



Sounds like for my shop the way to go might be to dedicate a cheap
easily rebuildable & easily discardable small CNC router for the
application. Put it in a box with light negative pressure (cheap
shop
vac) and call it a day.

'Sounds reasonable.


I don't really use any HSS except for hand ground lathe bits, drill
bits, and one specialty HSS lathe insert.

I have a little less than a small fortune in carbide mills on hand.

Non-specialists use carbide. Specialists use diamond. Most machining
of graphite today probably is done in EDM shops, where the volumes
are
not really large, and I've seen mostly carbide.

I used carbide on my SB 10L, and that machine does not like carbide
for turning steel. But the forces are quite low when machining
graphite -- if you try to take too big a bite it can crack -- and
machine rigidity is not much of an issue, except for the brittleness
of the workpiece.

Speeds are, basically, whatever ya' got. Feedrates are moderate, so
the tool doesn't climb and crack the work.

If you want some tips, you can call Poco Graphite. They're very
helpful and very expert.

--
Ed Huntress

When I milled carbon brushes for a Variac I found that I had to always
cut into the edge,
the material would crack off very easily where the cutting edge
exited. OTOH climb milling wasn't a problem.
-jsw

Yeah, it can be a little tricky. A lot has to do with the quality of
graphite you're using. Poco 3 is an industry standard for high-quality
electrodes. It's more resistant to chipping and cracking than the
cheaper stuff.

--
Ed Huntress