MACOR® Machinable Glass Ceramic Rod

MACOR® consists of interlocking plate-like mica crystals in a glassy matrix. These crystals stop microscopic fractures at the tool tip from spreading through the material, allowing it to be machined in a controlled way. During machining the tool pulverises the surface into a fine powder of crystals and glass — and because the crystals are so small, the machined surface finish is good. Its characteristics differ from metals and plastics, so it is worth spending a little time on simple trial cuts to learn how the material behaves before machining a finished component.

Tungsten carbide tools are highly recommended. High speed steel tools can be used but wear faster; ceramic-tipped tools are not advised. Watch for the warning signs of a dull tool: squeaking, a greyish surface finish through tool wear, or excessive cutting force. Sharpen the tool at the first sign of any of these. Machine at lower speeds, keep the workpiece cool, and take smaller depths of cut until you are confident with the material.

No. Unlike conventional ceramics, MACOR® requires no post-machining firing, sintering, or heat treatment. Once machining is complete the component simply needs to be cleaned and it is ready for use — no ceramic-specific processing equipment, no dimensional uncertainty from firing shrinkage.

Yes. Although MACOR® is a high-temperature material, the best machining results come from keeping both the material and the tool cool throughout. Water-soluble cutting fluids improve the cutting action, trap and wash away the abrasive powder generated during machining, and protect machine tools. If the fluid is recirculated, use a settling tank and give extra attention to cleanliness and machine maintenance.

With carbide-tipped tools, suggested turning speeds are around 600 rpm for 5–10 mm diameter rod, reducing to around 400 rpm at 25 mm diameter. Feed rates of 20–30 mm/min work well, with a depth of cut of 2–4 mm for roughing and under 1 mm for finishing. Side and back rake angles and end and side relief angles should be around 5°, with a side cutting edge angle of 15°–45° and a nose radius larger than 0.8 mm. Thread cutting is possible at low spindle speeds, with a typical cutting depth of 0.025–0.040 mm per pass.

Typical head speeds are 1,000–1,500 rpm with a chip load of 0.05 mm per tooth, and depths of cut as for turning (2–4 mm roughing, under 1 mm finishing). Use climb milling — it prevents material being pulled off the edge of the workpiece, which is the most common cause of edge chipping.

For holes up to about 5 mm diameter, a spindle speed of 1,000–1,500 rpm and a feed rate of 20–30 mm/min is effective. Relieve the drill flutes constantly — especially on small-diameter holes — and check drill sharpness every 25–50 holes. Use a slow feed at the start and finish of each hole. To prevent breakout when drilling through-thickness, use a backing plate or chamfer the hole entrance and exit before drilling through. MACOR® can also be ultrasonically drilled for very fine or unconventional hole geometries.

Yes. Make the clearance hole one size larger than recommended for metal (typically 0.1–0.2 mm larger) and chamfer both ends to prevent chipping. A 4-flute tap is preferable to a 2-flute tap. Run the tap slowly and in the same direction throughout — reversing can cause chipping — and flush with water or coolant to remove dust. Wire thread inserts can be used with MACOR® where threads will see repeated assembly.

Diamond grinding wheels give the best results, though silicon carbide and alumina wheels can also be used — always with water cooling. For polishing, start with 400 grit silicon carbide before moving to alumina or cerium oxide powders for the final finish. Polishing also improves compressive strength and arc resistance.

MACOR® is not resilient, so ensure clamping loads are uniformly distributed — use soft jaws where possible and avoid point contacts that could induce local stress concentrations. Avoid physical shock at every stage: in workholding, in tool engagement, and in handling between operations. This is especially important for small-diameter rod, which is more susceptible to fracture from uneven loading.

MACOR® has a continuous use temperature of 800 °C and a maximum no-load (peak) temperature of 1,000 °C. It will not creep or deform under sustained thermal load — making it a reliable substitute for high-temperature polymers in furnaces, processing equipment, and thermal break applications where plastics would soften or outgas.

MACOR® rod is available in a range of diameters, with a stock tolerance of +20% / −10% on diameter. This wider-than-metal tolerance is typical for machinable ceramics supplied as stock blanks — the expectation is that the rod will be turned to your final diameter. If you need a rod turned to a specific finished diameter, Goodfellow's machining service can produce it to your specification. Please contact us to discuss.

Rod is the natural starting point for any turned or bored component: standoffs, insulators, spindles, bushings, coil formers, laser aperture bodies, and vacuum feedthrough cores. The round cross-section suits components where a central bore or external turned profile is required, making it widely used in aerospace insulators, medical laser assemblies, RF components, and ultra-clean vacuum systems. It is also extensively used as a prototyping blank ahead of volume production in sintered ceramics.

Choose rod when the finished component is predominantly round in cross-section — turned insulators, standoffs, bushings, and bored bodies all start more efficiently from rod. Bar is better for prismatic components with flat reference surfaces such as brackets, mounting blocks, and housings. Sheet suits thin flat parts and components where a large face area is the dominant geometry. If your component straddles two forms, the one that minimises material removal and machining time is usually the right choice.

Choose MACOR® rod when in-house machinability, electrical insulation, and vacuum compatibility are the priorities. Shapal® Hi-M Soft offers significantly higher thermal conductivity in a machinable format, making it preferable where heat dissipation matters. If you need greater hardness, wear resistance, or higher continuous-use temperatures and can accept conventional ceramic processing, alumina (Al₂O₃) rod is the natural alternative. We stock all of these and can advise on the best fit.