Polycarbonate rod and block machining stock is supplied in extruded or compression-molded formats with sizes that are not governed by a single ISO product standard. The commercial window in converter catalogues extends from approximately 6 mm to 250 mm diameter for rod, and from 5 mm to 100 mm thickness for block, with plate formats commonly reaching 1 000 mm × 2 000 mm. Unfilled polycarbonate exhibits a density of 1.20 g/cm³ under ISO 1183-1, a glass transition near 147 °C under ISO 11357-2, and a water absorption at saturation of approximately 0.35% under ISO 62. The material is amorphous and does not exhibit a melting point; therefore thermal processing limits, annealing, and machining heat must be referenced to the glass transition and heat deflection behavior rather than to a crystalline melt temperature. General-purpose clear, transparent tinted, opaque black, and glass-fiber-reinforced grades are available, with glass fiber loadings commonly specified at 20% or 30% by mass. Because rod and block stock may contain regrind, extrusion orientation, or non-uniform cooling stresses, the purchase specification must require lot-specific thermal history and dimensional data in addition to resin grade.

Does Annealing Alter the Machining Response of Extruded PC Stock?

Annealing is specified to reduce frozen-in extrusion stress that causes movement during machining and stress cracking around bores or sharp corners. Extruded polycarbonate rod and plate cool non-uniformly, producing a compressive skin and a tensile core. When one face or diameter is machined away, the remaining stress state can warp the workpiece. Stress-relief annealing cycles in converter technical bulletins commonly run at 115 °C to 130 °C for 1 h per 10 mm of cross-section, followed by controlled cooling at or below 20 °C/h. Heating above 135 °C is not advised for close-tolerance stock because the material approaches the glass transition and dimensional registers may be lost. The correct cycle depends on cross-section, filler content, and whether the stock was extruded as hollow bar, solid rod, or plate. Published data for a universal annealing cycle across all stock diameters is limited; the converter should be required to supply the cycle used for the exact geometry.

Moisture must be controlled before annealing or hot forming. At 23 °C and 50% RH, polycarbonate may equilibrate near 0.15% to 0.20% moisture by mass, while the accepted pre-drying target for melt processing is below 0.02%. Oven drying at 120 °C for 4 h per 25 mm of wall thickness is frequently referenced for polycarbonate resin, but the actual drying time must be verified against moisture content measured by Karl Fischer or a moisture analyzer. Water absorption after 24 h immersion is 0.15% under ASTM D570; this value is representative for thin sections and should not be used as the equilibrium limit for thick block. Failure to remove moisture before thermal stress relief can generate surface splay, microvoids, and loss of optical clarity in transparent grades.

Chip Formation, Edge Cracking, and Tool Geometry

Machining of polycarbonate rod and block differs from machining acrylic or acetal because the polymer is ductile and heat-sensitive. Dull tools or negative rake geometries generate frictional heat that softens the surface above roughly 135 °C to 140 °C, producing smearing, chip welding, and edge breakout. Production tooling uses polished inserts with positive rake angles of 5° to 12° and clearance angles of 5° to 10° to shear rather than rub. For milling, solid carbide end mills with high helix angles and polished flutes are used. Spindle speeds from 6 000 min⁻¹ to 12 000 min⁻¹ with feed rates of 0.05 mm/tooth to 0.10 mm/tooth for 6 mm to 12 mm diameter tools are typical in unfilled stock. Published data for this specific configuration is limited, and starting parameters must be reduced if heat discoloration appears at the tool corner or if chips adhere to the bore.

Turning operations on unfilled polycarbonate typically use carbide inserts with a nose radius near 0.5 mm, depth of cut 1 mm to 3 mm, feed 0.05 mm/rev to 0.15 mm/rev, and surface speed 200 m/min to 500 m/min. Drilling requires a point angle of 90° to 110°, lip relief of 8° to 12°, and peck cycles or through-spindle air blast to evacuate chips. Dwell at the bottom of a hole concentrates frictional heat and creates local softening that leads to oversized, smeared bores. Coolant compatibility is critical: water-miscible coolants or plain air blast are preferred. High-pH synthetic coolants above approximately pH 9 can craze stressed polycarbonate, and oil-based fluids containing esters or petroleum fractions may act as environmental stress-cracking agents on loaded features.

Glass-fiber-reinforced grades are more abrasive than unfilled stock. Field reports from fabricators describe edge breakout when step-over exceeds 0.5 mm in 20% glass-filled polycarbonate on a vertical machining center with a 12 000 RPM spindle. Tool supplier data indicate that glass-filled polycarbonate requires finer step-over, higher cutting speed, and lower feed per tooth than unfilled stock. Diamond-like-carbon or CVD diamond-coated tools are specified for extended runs because fiber abrasion reduces tool life. The exact tool life reduction is grade- and coating-dependent; published data for this specific configuration is limited, and tool supplier test data should be requested for production quantities.

If the Application Requires Transparency or Flame Retardancy

Transparent general-purpose polycarbonate stock is selected when visible light transmission and dimensional stability are required simultaneously. ASTM D1003 total luminous transmittance for clear unfilled sheet is commonly above 88% with haze below 1.0%, but rod and block may exhibit edge effects from extrusion and saw cutting. Yellowness index should be requested under ASTM E313 for outdoor or aesthetic parts. If flame retardancy is required, the converter must supply a UL 94 V-0 yellow card for the specific stock thickness and color. Flame-retardant polycarbonate grades may be opaque; transparent sulfonate-based formulations exist but may exhibit reduced chemical resistance and altered notched impact behavior compared with general-purpose clear grades. For food-contact applications, request 21 CFR 177.1580 compliance for the polycarbonate resin. For electrical insulation, request dielectric strength under ASTM D149 or IEC 60243-1 and comparative tracking index under IEC 60112. REACH and RoHS declarations should accompany each lot for regulated markets.

Chemical incompatibility must be evaluated against the intended service environment. Polycarbonate is attacked by methylene chloride, acetone, methyl ethyl ketone, toluene, and ammonia. Stress-cracked parts can fail at loads far below the short-term tensile yield of 60 MPa to 70 MPa under ISO 527-2. Cleaning agents containing amines, esters, or aromatic hydrocarbons should not be used on machined polycarbonate parts unless the stress state is known to be low. Isopropanol can also craze highly stressed sections, so mild soap solution or a converter-approved cleaner is the safer cleaning boundary for critical components.

Stock size standardization and tolerance classes are supplier-defined

Polycarbonate rod and block are not covered by a single ISO product standard equivalent to ISO 7823 for cast acrylic sheet. The purchaser must state the dimensional standard in the order. Rod diameter is often supplied with an oversize allowance for finishing. For rod diameters up to 40 mm, diameter tolerance from converter stock may be specified as +0.5 mm / -0.0 mm; diameters above 100 mm may require +1.0 mm / -0.0 mm. General tolerances are commonly related to ISO 2768-1 class m or k, but not all converters certify to that class. Blocks are specified by thickness, width, length, and flatness. Flatness over 1 000 mm may be 0.5 mm to 1.0 mm for extruded plate, while machined plate may be held to 0.1 mm to 0.3 mm. These values are representative supplier capabilities, not universal standards; published data for this specific configuration is limited.

A purchasing specification for polycarbonate rod and block should require the following information from the converter: polymer grade and filler type; melt flow rate under ISO 1133-1:2022 at 300 °C/1.2 kg; tensile properties under ISO 527-2:2012 or ASTM D638-14; notched Izod under ISO 180/A:2023 or ASTM D256; deflection temperature under ISO 75-2:2013 at 1.8 MPa; density under ISO 1183-1:2019; water absorption under ISO 62:2008; and flammability certification under UL 94. If optical clarity is required, request ASTM D1003 light transmission, haze, and yellowness index. If dimensional stability is critical, require the annealed condition and specify the maximum allowable bow, twist, and flatness over the full length or plate area. Request a certificate of conformance for each lot and, for regulated markets, REACH and RoHS declarations.

For annealed stock, request the annealing temperature-time curve and cooling rate; for moisture-sensitive processing, request moisture content in percent or parts per million. If post-machining stress relief is needed, specify that finished parts be annealed after roughing and before final finishing. Without this, holes and sharp corners can display crazing after exposure to cleaning agents or ambient humidity. For glass-filled stock, request the exact glass fiber content by weight and whether the reinforcement is chopped glass fiber or glass bead, because machined surface finish and tool wear differ. Validation of machinability on the actual stock lot is required because regrind content, filler distribution, and annealing history alter chip formation and stress-cracking resistance. A first-article trial involving roughing, annealing, finishing, and exposure to the intended service chemical is the only reliable method to confirm that the supplied polycarbonate rod or block meets the application boundary.