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Machining MACOR®

The ugly truth about this “machinable” ceramic that I learned building my first plasma thruster.

MACOR® is a “machinable” ceramic that’s sometimes used in Electic Propulsion thrusters among other things.

Here are some notes on machining MACOR®:

  1. Use Boron Nitride instead.
  2. If you (like me) already blew your budget on buying MACOR® stock, you must use coolant while machining. Else it will crack.
  3. Ideally, use carbide end mills. Some machine shops (including Rose-Hulman’s PHOE Department machine shop) only have high-speed steel, which wears out FAST when working with MACOR®, and then it will crack.
  4. It may randomly crack.
  5. Buy some ceramic glue to put together broken parts if you don’t have the budget to buy new stock.
The stupid MACOR® part that cracked during machining. This picture was taken after a successful run of my first Gridded Ion Thruster
The MACOR® section in the partially assembled Ion Thruster (pre-operation)
Gridded Ion Thruster just before our first successful Ignition Test. I had to tape up the MACOR® section to prevent any further leaks from the crack that had formed.

Boron Nitride (h-BN) ceramic is as pricy, but it’s very chill! Easy to machine with steel bits. I would recommend BN for your day-to-day Electric Propulsion experiments but would be more careful about material selection for your actual space missions.
“It’s like machining butter” -Roger Sladek, PHOE machinist, about h-BN.

I managed to raise some more funding for my research, so I got two pieces of Boron Nitride ceramic stock that was machined to replace the broken MACOR® section. You can make more precise shapes with BN.

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