Ned Advice Before I Spend

[Kurr]

Hello,

I own a small shop that currently produces micro ( 1 oz or less) silver and gold bullion. The shop that i have used for stamps is no longer able to provide for my needs and I was wanting to move production in house,

I have put back enough for the G0704 which i then planned on converting to CNC. Upon reflection, this might be overkill. I am looking for an end product that will be solely for small work such as graphite and steel molds with max dimensions around 9Lx4Wx4D (in graphite) and stamps, coining hubs/dies and punch and dies for blanks. Most dies/stamps will be O2, lets assume hardened.

If worst comes to worst, I have an EDM shop withing 15 miles of my house that charges $75 an hour and I am thinking I could mill my own graphite/copper electrodes and have the produce the finished dies/stamps.

Since this will be dedicated to small footprint jobs, is there anything I am missing? Would my money be better spent on a smaller factory cnc machine such as a Taig or Sherline? I understand for engraving I need a higher RPM. Also since I am not a job shop, speed of work is not an issue. I do not care if it takes many hours to produce as I have had a stamp/die in use for 6 years or so and it is still producing good work for me.

I have no machining experience, my neighbor is a retired machinist (manual, no cnc experience) and am currently setting on the path to learn cad/cam.

Please give me your thoughts and or advice upon my situation and I will happily answer any questions I can.

Thank you,
Kurr

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[awerby]

The smaller the bits you use, the faster you need to spin them. So that's an argument for the Taig, or a Sherline with the high-speed pulley set, which can spin at 10,000 RPM. However, graphite is difficult stuff to work with. Even though it's sometimes used as a lubricant, when you cut it, it acts as an abrasive, which gets into the slides and screws and damages them. So you'd need to protect the moving parts of your machine better than they usually are, by providing bellows or a similar shielding apparatus. The other problem with it (besides the horrible mess it makes) is that the dust is electrically conductive, so if it gets into your computer, you can kiss it goodbye (carefully, in case it bursts into flames). I suppose there are ways of preventing this from happening - you might make another post asking if anyone has any suggestions on that.

[Kurr]

Thank you for your reply, I hand't considered that graphite was conductive. A filtered vacuum system wouldn't be hard to construct. That should protect both mechanical and electronic parts.

I would really prefer to only mill graphite for certain ingot molds. My main at the moment is on the O2 dies stamps and punch/die combos for punching blanks.

[Jim Dawson]

Rather than EDM the dies, why not buy the O2 in the unhardened condition, engrave it directly and then harden it. That way it's a one step process (or 2 if you count the heat treat) Saves building several electrodes, and it's not messy. As Andrew says, graphite gets all over everything. In either case, you will need a high speed spindle. Hanging a small router motor off of your quill is a cheap way to get a high speed spindle. You don't need a lot of power for the size bits you will be using. I use a Harbor Freight pencil die grinder on my machine for a high speed spindle.

[Zorbit]

Regarding the dust extraction when machining graphite: Photocopier engineers face a similar hazard, when I worked on them I used a "Tonervac" which was a small cleaner with a sealed box containing a very fine filter similar to a car air cleaner. The box/filter assembly was disposable. I think that would be a safe way for you to dispose of the dust.