MACOR® Machinable Glass Ceramic Bar

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 more quickly; ceramic-tipped tools are not advised. The warning signs of a dull tool are squeaking, a greyish surface finish from tool wear, or excessive cutting force — stop and sharpen at the first sign of any of these. Machine at lower speeds, keep the workpiece cool, and take smaller depths of cut, especially on exposed corners and edges where chipping is most likely.

No. 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 — a key advantage over conventionally processed ceramics, where firing introduces dimensional uncertainty and requires specialist equipment.

Yes. Water-soluble cutting fluids improve the cutting action and are especially important when milling bar, where the extended contact between tool and workpiece generates more heat than a short drilling or facing operation. Coolant traps and clears the abrasive machining powder, protecting both the surface finish and the machine tool. Use a settling tank if the fluid is recirculated.

Typical head speeds are 1,000–1,500 rpm with a chip load of 0.05 mm per tooth and depths of cut of 2–4 mm for roughing and under 1 mm for finishing. Use climb milling throughout — it is essential when milling MACOR® bar because conventional (up) milling tends to pull material off the edges, causing chipping that is particularly visible on the flat faces and corners of rectangular stock.

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. Feed slowly at both entry and exit, and use a backing plate or chamfer the exit face before drilling through to prevent breakout. MACOR® can also be ultrasonically drilled for tight-tolerance or unconventional bore 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. Use a 4-flute tap run slowly and continuously in one direction — reversing causes chipping — and flush with water or coolant throughout. Wire thread inserts can be used in MACOR® where threads will see repeated assembly or load.

Use a carbide grit blade at a band speed of around 30 m/min, or a diamond or silicon carbide cut-off wheel. Support the bar evenly and keep the cut cool with water-soluble coolant. MACOR® is brittle — avoid physical shock and sudden loading at every stage, including when positioning the bar and starting or finishing the cut.

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 move to alumina or cerium oxide powders for the final finish. Polishing flat faces significantly improves compressive strength (up to 900 MPa vs 345 MPa as-machined) — worthwhile for components used in high-load or high-voltage applications.

Ensure clamping loads are uniformly distributed and avoid point contacts that can introduce stress concentrations — use soft jaws or a compliant pad. The flat-sided geometry of bar makes it easier to fixture uniformly than round rod, but the corners are still vulnerable to chipping from uneven clamping or vibration. Avoid all physical shock throughout workholding, tool engagement, and part transfer.

MACOR® bar has a continuous use temperature of 800 °C and a maximum no-load (peak) temperature of 1,000 °C. Unlike high-temperature polymers, it will not creep or deform under sustained thermal load — making it suitable for furnace fixtures, thermal break blocks, and high-temperature mounting structures where dimensional stability is essential throughout the service life.

MACOR® bar is available in cross-sections from 6 mm to 50.8 mm and lengths from 25 mm to 300 mm. Side length tolerances are ±10% for sides ≤10 mm and ±1 mm for sides over 10 mm. Length tolerances are ±1 mm for lengths under 100 mm and +5% / −1% for lengths of 100 mm and over. If you need bar cut to a specific length or machined to tighter tolerances, Goodfellow's machining service can supply finished parts — please request a quote.

Bar is the natural starting point for any prismatic component with flat reference surfaces: mounting blocks, brackets, spacers, housings, fixture plates, and electrical isolation blocks. The rectangular section simplifies fixturing when milling and minimises material waste compared with cutting prismatic parts from sheet or from round rod. Common applications include high-voltage insulation blocks, vacuum chamber mounting structures, laser assembly spacers, and thermal break components in high-temperature industrial equipment.

Choose bar when the finished component has a predominantly rectangular cross-section with flat reference surfaces — brackets, blocks, and housings all start more efficiently from bar than from round rod, and with less waste than cutting from sheet. Rod is better for turned or bored round components. Disk suits thin flat circular parts within the stock diameter range. Sheet is the right choice for large flat faces, thin sections, or non-circular flat outlines.