MACOR® Machinable Glass Ceramic

Yes. There is no minimum order quantity on any Goodfellow MACOR® product. We supply single rods, individual sheets, and small machined components as standard — at the same price and with the same full documentation as a bulk order. This applies to every stock size and form in the range.

MACOR® is a machinable glass ceramic developed by Corning, consisting of randomly oriented mica crystals dispersed in a borosilicate glass matrix. Unlike conventional technical ceramics, which require diamond grinding or green-state machining followed by a firing cycle of several weeks, MACOR® machines directly to finished dimensions with standard carbide tooling — no firing or post-processing required beyond cleaning. During machining, the mica crystals fracture along natural cleavage planes, stopping cracks from propagating through the bulk material. This gives metal-like chip formation and a good as-machined surface finish while retaining ceramic thermal, electrical, and dimensional properties.

MACOR® is rated for continuous use at 800°C, with short-term peak excursions to 1000°C. This significantly exceeds the capability of any engineering plastic — PEEK, for comparison, is limited to approximately 250°C continuous — while MACOR® retains dimensional stability and shows no creep under load at these temperatures, unlike polymers above their glass transition or softening points.

MACOR® routinely machines to ±0.02mm using standard carbide tooling, with tolerances as tight as ±0.005mm achievable on critical features. This is tighter than is reliably achievable with most engineering plastics, where moisture absorption and thermal expansion limit precision, and avoids the shrinkage variability (±0.5–1%) inherent to fired sintered ceramics. Achievable surface roughness (Ra) of 0.4–0.8 μm is possible directly from machining, with progressive polishing from 400-grit silicon carbide producing mirror finishes where required.

Sharp tungsten carbide-tipped tools are strongly recommended; high-speed steel can be used but carbide gives better tool life and surface finish, and ceramic-tipped tools are not advised.

• Turning: around 600 rpm for 5–10mm diameter rod, reducing to around 400 rpm for 25mm rod, with feed rates of 20–30 mm/min and depths of cut of 2–4mm for roughing, less than 1mm for finishing.
• Milling: typically 1000–1500 rpm with a chip load of around 0.05mm per tooth; use climb milling to prevent material being pulled off the edge.
• Drilling: 1000–1500 rpm with a 20–30 mm/min feed, relieving the drill flutes frequently and using a slow feed at hole entry and exit to prevent breakout.

Water-soluble cutting fluid is recommended throughout to keep both tool and workpiece cool, improve cutting action, and wash away the fine abrasive powder generated during machining.

Yes. MACOR® can be drilled, tapped, and thread-cut, which is not generally possible with softer machinable ceramics such as boron nitride. For tapping, the clearance hole should be made one size larger than the metal equivalent (typically 0.1–0.2mm larger), with both ends chamfered to prevent chipping; a 4-flute tap run slowly in a single direction (avoiding back-and-forth motion) with water or coolant flush gives the best results, and wire thread inserts can also be used. Thread cutting on a lathe is performed at low spindle speeds with a typical cutting depth of 0.025–0.040mm per pass. Holes up to approximately 5mm benefit from a backing plate or chamfered entry/exit to prevent breakout, and it is also possible to drill MACOR® ultrasonically.

Yes. MACOR® has zero porosity, so there are no trapped gases to outgas under vacuum — a key advantage over sintered ceramics and polymers, which typically retain residual porosity or absorbed moisture. After proper bakeout, outgassing rates below 1 x 10⁻¹² mbar·L·s⁻¹·cm⁻² are achievable, comparable to 316L stainless steel and orders of magnitude better than most polymer alternatives. This makes MACOR® a standard choice for synchrotron beamlines, particle accelerator vacuum systems, dilution refrigerator feedthroughs, and other instrumentation operating down to 10⁻¹⁰ mbar.

MACOR® is an excellent electrical insulator with high dielectric strength and a volume resistivity of approximately 10¹⁷ Ω·cm — around ten times higher than Shapal Hi-M Soft and roughly an order of magnitude higher than PEEK. Its dielectric constant is approximately 6.0 at 1 MHz, falling to around 5.7 at 10 GHz, with a loss tangent below 0.003 at microwave frequencies and at cryogenic temperatures (4K). This combination of low loss and high resistivity makes MACOR® widely used for high-voltage feedthroughs, waveguide windows, antenna supports, and electrical insulators in superconducting and RF systems.

Yes. MACOR® withstands gamma radiation doses of 10 MGy with less than 0.01% dimensional change and minimal degradation of mechanical or electrical properties. This compares favourably with polymers, which typically embrittle above 100 kGy, and with some ceramics that develop colour centres affecting optical or electrical performance under irradiation. This radiation hardness, combined with dimensional stability, underpins its use in particle physics detector mounts, cryogenic magnet insulation, and other high-radiation environments where long-term positional accuracy is critical.

Yes. MACOR®'s coefficient of thermal expansion (9.3 x 10⁻⁶/°C) closely matches kovar, stainless steel, and common sealing glasses, allowing hermetic MACOR®-to-metal seals that survive repeated thermal cycling. Active metal brazing using silver-copper-titanium alloys at 650–850°C achieves leak rates below 1 x 10⁻¹⁰ mbar·L·s⁻¹. For thin-film metallization, sputter-deposited titanium/platinum/gold layers achieve adhesion strengths exceeding 50 MPa and survive over 1000 thermal cycles, supporting electronic packaging and feedthrough applications. Brazed MACOR® feedthroughs have demonstrated hermetic performance through over 20 years of -120°C to +120°C cycling in low Earth orbit.

MACOR® and alumina occupy different points in the cost-versus-performance trade-off. MACOR® wins on machinability (standard carbide tools versus diamond grinding or green-state machining plus firing), lead time (48-hour stock versus 4–12 weeks for custom alumina parts), tolerance capability (±0.02mm versus ±0.5–1% shrinkage variability), complex internal geometries, and hermetic sealing. Alumina wins on maximum operating temperature (1600–1750°C versus 800°C), hardness (Knoop 1200–1600 versus 250), flexural strength (300–400 MPa versus 94 MPa), chemical resistance, wear resistance, and material cost per kilogram at high volumes. A common strategy is to prototype and validate designs in MACOR®, then transition proven geometries to alumina for production runs above roughly 500–1000 units.

MACOR® and PEEK serve different operating envelopes. MACOR® offers a substantially higher continuous use temperature (800°C versus 250°C), no creep under load at elevated temperature, higher rigidity, roughly 5x better dimensional stability (lower CTE), three times the compressive strength, zero outgassing for ultra-high vacuum, and significantly better radiation resistance. PEEK wins on ease and speed of machining, impact resistance (MACOR® is brittle and fractures rather than absorbing impact energy), lower material cost, weight (PEEK is roughly half the density), and chemical resistance to a broader range of media. As a general rule, choose MACOR® above 250°C, in vacuum, or where dimensional stability under load is critical; choose PEEK where impact resistance, rapid machining, or biocompatibility are the priority.

The key distinction is thermal strategy. Shapal Hi-M Soft has a thermal conductivity of approximately 92 W/m·K — around 60 times higher than MACOR®'s 1.46 W/m·K — making it a thermal conductor with electrical insulation, suited to heat spreaders and high-power electronics substrates. MACOR® is the opposite: a thermal insulator, used to create heat breaks between temperature zones. MACOR® is the better electrical insulator (volume resistivity roughly 100x higher), is easier to machine, has broader availability with 48-hour stock dispatch, and is more economical. Shapal has a higher maximum continuous use temperature (1000°C versus 800°C), better thermal shock resistance, and higher flexural strength. Choose MACOR® for thermal insulation combined with high-voltage electrical insulation; choose Shapal where heat must be conducted away from a component while maintaining electrical isolation.

MACOR® is generally easier to machine than hot-pressed boron nitride, achieving tighter tolerances (±0.02mm versus ±0.05–0.1mm) with standard carbide tooling rather than the carbide or diamond tooling BN can require. MACOR® can also be reliably drilled, tapped, and threaded, whereas BN's softness makes threads prone to stripping. MACOR® offers better electrical insulation, higher dielectric strength, and significantly higher compressive and flexural strength. Boron nitride's advantages are its much higher thermal conductivity (20–60 W/m·K versus 1.46 W/m·K) where heat transfer is wanted, a higher maximum temperature in inert or vacuum environments (1800–2000°C versus 800°C), superior thermal shock resistance, and non-wetting behaviour against molten metals. Choose MACOR® for precision electrical insulators and threaded fasteners in oxidising atmospheres up to 800°C; choose BN for crucibles, molten metal contact, or applications above 1000°C in non-oxidising conditions.

Goodfellow operates under an ISO 9001 quality management system, and our MACOR® range complies with EU Directives 2015/863/EU (RoHS 3) and 2000/53/EC (ELV). Material certification and traceability documentation can be requested at time of order. Goodfellow maintains a direct supply relationship with Corning, the originator and manufacturer of MACOR®, ensuring consistent material quality and supply continuity.

Standard stocked MACOR® sizes — rods, bars, sheets, and slabs — are dispatched within 48 hours. Delivery is free worldwide, with no minimum order value required, and customs clearance is handled on your behalf.

Yes. For complex geometries, we work with specialist machining partners for whom precision ceramic machining is a core part of their business, ensuring expert handling of custom MACOR® components. Our Microfabrication team can also produce laser-cut and precision-machined parts, custom-geometry test samples, and prototype components. For projects moving toward higher volumes, our supply model follows the typical development pathway: rapid in-house or partner machining for prototyping and design validation, followed by a production decision — continuing with MACOR® for low-to-medium volumes, or transitioning a validated geometry to a sintered ceramic such as alumina for high-volume production. Contact us to discuss your project's requirements at any stage.