MACOR® Machinable Glass Ceramic Disk

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 for all secondary operations — drilling, chamfering, facing, and lapping. High speed steel tools can be used but wear faster; ceramic-tipped tools are not advised. Watch for tool wear signs (squeaking, a greyish surface, or excessive force) and sharpen immediately. Machine at lower speeds and take smaller depths of cut, particularly on the thin edges of a disk where the risk of chipping is highest.

No. MACOR® requires no post-machining firing, sintering, or heat treatment of any kind. Once secondary operations are complete the component simply needs to be cleaned and it is ready for use — which is one of the main practical advantages of MACOR® over conventionally processed ceramics.

Yes. Water-soluble cutting fluids improve the cutting action, trap and wash away the abrasive powder generated during machining, and protect your tooling. Keep both the material and the tool cool throughout all operations. If coolant is recirculated, use a settling tank — the machining powder is abrasive and will accelerate wear in unprotected machine components.

For holes up to about 5 mm diameter, use a spindle speed of 1,000–1,500 rpm and a feed rate of 20–30 mm/min. Relieve the drill flutes constantly — especially for small-diameter holes — and check sharpness every 25–50 holes. Use a slow feed at both the entry and exit of the hole, and place a backing plate under the disk or chamfer both faces before drilling through to prevent breakout on the exit face. MACOR® can also be ultrasonically drilled where tight-tolerance or unconventional bore geometries are needed.

Facing, slot milling, chamfering, and profiling are all feasible on a disk with the right setup. Use climb milling to prevent material being pulled off the edges. Typical head speeds are 1,000–1,500 rpm with a chip load of 0.05 mm per tooth and continuous coolant. Ensure the disk is evenly supported and clamped with soft jaws or a compliant pad to distribute the clamping load — MACOR® is brittle and will fracture under concentrated point loads.

Yes. Make the clearance hole one size larger than recommended for metal (typically 0.1–0.2 mm larger) and chamfer both ends. Use a 4-flute tap, run it slowly and in one direction only — reversing can cause chipping — and flush with water or coolant throughout. Wire thread inserts can be used where threads will see repeated assembly or significant mechanical loading.

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, then progress to alumina or cerium oxide powders for the final finish. Polishing a MACOR® face improves its compressive strength (up to 900 MPa after polishing vs 345 MPa as-machined) and arc resistance — both valuable for disk-format insulators and window components.

MACOR® is not resilient — ensure clamping loads are uniformly distributed across the face and avoid point contacts. Use soft jaws or a compliant backing pad. Avoid physical shock at every stage. Thin disks are particularly vulnerable to fracture from uneven clamping or from vibration during drilling, so set up and feed rates conservatively until you have confirmed the material behaviour with your specific equipment.

Yes. MACOR® has zero porosity and does not outgas, making it fully compatible with high-vacuum and ultra-high-vacuum environments. It can be hermetically sealed, joined, and metallised — which supports its use as a vacuum window blank, isolation disk, or sealed assembly component. Its coefficient of thermal expansion is readily matched to most metals and sealing glasses, minimising stress at sealed interfaces.

MACOR® disk 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, which is why it is used as a thermal break and isolation disk in furnaces, high-temperature processing equipment, and laser assemblies where polymers would fail.

MACOR® disk is available in thicknesses from 1 mm to 6 mm and diameters from 10 mm to 50.8 mm, with a diameter tolerance of ±0.5 mm and a thickness tolerance of ±20%. The diameter tolerance is tighter than for rod or bar stock, as disks are typically used in close-fitting axial assemblies. If you need a finished disk to tighter tolerances or a non-standard diameter, Goodfellow's machining service can produce it — please request a quote.

The disk geometry suits components that mount axially, act as isolation barriers, or serve as flat window or substrate blanks. Common uses include electrical isolation disks between conductive assemblies, thermal break spacers in furnace fittings, vacuum window blanks (further drilled and lapped), and dielectric spacers in RF and microwave assemblies. The disk can be used as-supplied or further machined — drilled, chamfered, faced, or lapped — to the finished specification.

Choose a disk when the component is circular in plan and the diameter is within the stock range (10–50.8 mm). It avoids the material waste and sawing step that would be needed if you were cutting a disk from sheet. Rod is better when a through-bore or turned outer profile is required and the diameter exceeds the disk range. Sheet suits flat parts with larger face areas or non-circular outlines. Bar suits prismatic components with flat reference surfaces.