Guides / Materials
Macor and Machinable Ceramics: Fast, Forgiving and Often Misused
May 11, 2026
Machinable glass ceramics sit in their own corner of this niche. Macor is the best known: a mica crystal structure grown inside a borosilicate glass matrix. The mica platelets let a cutting edge break tiny fragments loose instead of propagating a crack, so the material cuts on ordinary carbide tooling on an ordinary machining centre.
No sintering afterwards. No shrinkage to model. No diamond wheel queue. The part that comes off the machine is the finished part.
What that buys you
- Speed. A fixture that would take weeks as a ground alumina part can be cut in days.
- Zero porosity. It is vacuum tight as machined, which matters for instrument work.
- Good dielectric behaviour and no outgassing worth worrying about in most vacuum systems.
- Complex geometry. Undercuts, pockets, threads and fine features that would be painful or impossible to grind.
- Revision tolerance. When the design changes at prototype stage, the cost of the change is machine time, not a new pressing tool and a firing slot.
What it costs you
Macor is weak compared with the sintered oxides. Flexural strength lands near 94 MPa, against 300 to 400 MPa for alumina and around 1000 MPa for 3Y-TZP. It is also soft by ceramic standards, so it wears where alumina would not.
That rules it out for:
- Load bearing parts and anything under sustained stress
- Wear surfaces, seal faces, guides and anything sliding against a hard counterface
- Hot structural work above roughly 600 degrees C under load
- Abrasive or high pressure flow paths
The other cost is the blank. Macor is a specialty product from a single primary source and the billet price is high. On a small part with simple geometry, ground alumina can still be cheaper overall.
Where it genuinely wins
Instrument and laboratory parts. Sample holders, insulating spacers, probe mounts, vacuum feedthrough bodies. Low stress, high geometric complexity, small quantities.
Fixtures and setters for the rest of a process, including fixtures that hold other ceramics.
Prototype versions of a production part. Cut the first article in Macor to prove fit and function, then commit to alumina or zirconia once the geometry is settled. It is far cheaper to be wrong in a machinable material.
Electrical standoffs and masks in equipment that gets modified constantly.
The alternatives in the same family
- Shapal Hi M Soft, a machinable aluminium nitride and boron nitride composite, when the part also has to move heat. See aluminium nitride vs alumina.
- Boron nitride, softer still, self lubricating, excellent at very high temperature but porous and easily damaged.
- Machinable glass ceramics from other suppliers, which are close enough in behaviour that the choice often comes down to available billet sizes.
How to decide in one pass
Ask what happens if the part deforms or wears slightly. If the answer is “the experiment fails” then Macor is fine. If the answer is “the machine stops” then you want a sintered ceramic, and the real question becomes which route to machine it on. That is covered in green machining or hard grinding.
One more practical note: do not put a machinable ceramic on a drawing with tolerances copied from a ground alumina part. Ask for what the function needs. The reasoning is in realistic tolerances and surface finishes.
For where machinable ceramics sit against sintered grades, see ceramic material selection.
See also: the Macor reference page.
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Frequently asked questions
Why is Macor expensive if it is easy to machine?
The material itself is costly to produce in billet form and it comes from a single source, so the blank price is high. What you save is grinding hours, lead time and the firing step, which on a one-off part usually more than pays for it.
How hot can Macor go?
Around 800 degrees C continuous and roughly 1000 degrees C for short peaks, but it starts to deform under load well before that. Treat 600 degrees C as a sensible working limit for a loaded part.
Can Macor hold tight tolerances?
Yes, down to about ±0.013 mm on a machined feature with care, and it takes a fine finish. It is far less strong than alumina or zirconia, so it is not a structural material.
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