Polycarbonate Sheet Size Chart: Thickness, Panel Size and Tolerances in One Table

Extruded polycarbonate sheet is specified in procurement documentation by nominal thickness, mill panel dimensions, and the permitted deviation from those values. The consolidated table below aligns representative thickness tolerances, standard panel sizes, and cut-to-size length/width tolerances in one reference for transparent enclosures, machine guards, signage, and thermoforming stock. Dimensional acceptance follows ISO 7823-1:2003 for extruded polycarbonate sheet and ASTM D6098-16 where North American material certification is required. The base resin is dried and melted through a flat die, so final sheet tolerance is not a single material property but a process variable controlled by melt pressure, die lip adjustment, polishing roll gap, and downstream puller speed. Published data for proprietary UV-protected, flame-retardant, or hard-coated sheet configurations may differ; the lot test certificate controls acceptance.

The values shown in the table are consolidated from general-purpose extruded polycarbonate sheet. They are procurement reference values, not blanket acceptance criteria for optical, flame-retardant, hard-coated, multiwall, or corrugated polycarbonate. Thickness tolerance for machined polycarbonate sections with post-machining planing may be tighter than the extruded sheet tolerance but is not covered by the table. For custom sheet lengths above 3,050 mm, width tolerance generally remains controlled by the master web width, while length tolerance is set by the sheeting saw and should be fixed in the purchase specification.

What tolerance bandwidth is specified for extruded polycarbonate sheet?

The thickness tolerance bands in the table are tied to the extruded sheet classification in ISO 7823-1:2003 and ASTM D6098-16. Thickness is measured with a calibrated dial indicator or scanning thickness gauge according to ISO 4593:1993 or ASTM D5947-18. In commercial practice, measurement positions are distributed across the web and along the machine direction, with edge trim excluded. The tolerance applies to each point, not only to the arithmetic mean. A sheet that averages within tolerance but has one local point outside the band is rejected unless the purchase specification defines a different acceptance rule.

Panel width and length tolerances are controlled by the sheeting saw or guillotine in cut-to-size work. Standard mill panels are typically supplied to a squareness tolerance of 0.5 mm/m unless otherwise agreed. For non-square or routed panels, the purchase specification must state whether tolerances apply to the as-cut panel or the post-conditioned panel. Polycarbonate has a coefficient of linear thermal expansion of approximately 65 × 10⁻⁶ K⁻¹ to 70 × 10⁻⁶ K⁻¹. A temperature difference of 20 K changes a 2,050 mm wide panel by 2.6 mm to 2.9 mm. Dimensional acceptance therefore requires a stated reference temperature, commonly 23 °C ± 2 °C. Water absorption after 24 h at 23 °C is approximately 0.15 %; at saturation, approximately 0.35 %. Dimensional change from moisture absorption is smaller than thermal expansion but can still contribute 0.1 % to 0.2 % to linear dimensions. A 2,050 mm dry panel may therefore gain 2 mm to 4 mm in width if stored unwrapped under high-humidity conditions without edge protection.

Die lip adjustment, melt pump stability, and roll stack pressure

Thickness variation in polycarbonate sheet originates in the flat die and is amplified or corrected in the polishing stack. On a production line using a 30:1 to 36:1 L/D single-screw extruder with a barrier screw and Maddock mixing section, resin is processed at melt temperatures of 260 °C to 300 °C through a flat T-die. The die is fitted with a flexible lip or restrictor bar; local die-bolt adjustment changes the lip gap and therefore the local mass flow. A melt pump between screw tip and die reduces screw-speed variation and maintains steady die inlet pressure. Without a melt pump, screw surge can produce machine-direction thickness variation even when the average gauge remains acceptable.

Polycarbonate resin must be dried before extrusion. A closed-loop desiccant dryer with a dew point of -40 °C or lower, air temperature of 120 °C, and residence time of 4 h is used to reach a moisture content below 0.020 %. If residual moisture exceeds 0.030 %, hydrolysis of carbonate linkages reduces molecular weight. The resulting melt viscosity drift changes die pressure and produces sheet thickness instability. A vented extruder barrel is not a substitute for pre-drying.

The polishing stack controls surface finish and final gauge. Thin sheet is typically run through a three-roll stack with roll surface temperatures between 110 °C and 160 °C. Thick sheet requires lower roll temperatures and higher roll gap pressure to remove heat from the core. The process conflict is that excessive roll gap pressure can squeeze the melt toward the edges, while insufficient pressure reduces contact cooling and leaves the core above the polycarbonate glass transition temperature of approximately 147 °C. If the core leaves the stack above that temperature, post-exit recovery changes width and thickness after the haul-off. For sheet from 10 mm to 25 mm, the line speed is reduced to permit core cooling, and the sheet is often cut slightly oversize before final dimensioning. On a 2,050 mm wide line, a roll face temperature differential of 3 K to 5 K across the web can create measurable thickness variation, particularly in matte or textured sheet. Published data for this specific configuration is limited because roll surface conditions and sheet finish class interact with the temperature differential.

Downstream puller speed controls machine-direction length. Closed-loop optical edge detection adjusts draw ratio to maintain length tolerance when the sheet is cut in-line. Off-line sheeting saws use a positional tolerance of ±1 mm to ±2 mm on standard panels, with repeatability dependent on saw carriage rigidity and sheet clamping. Cut-to-size tolerance is therefore not identical to mill panel tolerance unless the same measurement reference is used.

When fire-rated polycarbonate sheet changes dimensional tolerance at purchase and during fabrication

Flame-retardant polycarbonate sheet rated to UL 94 V-0 at 3.0 mm may carry phosphate ester or brominated additives that alter melt rheology, moisture absorption, and thermal expansion. The dimensional tolerance of these grades is not automatically identical to unfilled polycarbonate. In a vacuum forming line using a 2,050 mm × 3,050 mm flame-rated panel, the incoming sheet width may be recorded over nominal after 48 h at 60 % relative humidity, while the unmodified polycarbonate control remains within a narrower band. Published data for specific proprietary flame-retardant formulations is limited, and lot qualification should include a dimensional check after conditioning at the intended service relative humidity.

Phosphate ester flame retardants can plasticize polycarbonate, reducing heat deflection temperature and increasing water uptake. That creates an operational boundary for dimensionally critical parts: the sheet must be conditioned in the fabrication environment for a stated period before cutting, otherwise the routed or formed dimensions can drift after installation. Chlorinated solvents, ketones, aromatic hydrocarbons, and amine-based cutting fluids cause environmental stress cracking of polycarbonate and must be excluded from fabrication areas. Cleanup with alkaline detergents should be followed by thorough rinsing because residual alkali can attack the polymer surface. Flame-retardant polycarbonate sheet should be stored in polyethylene film; trapped condensation can create local moisture absorption and non-uniform dimensional change.

Panel flatness for polycarbonate sheet is commonly specified as the maximum deviation from a reference plane over a stated length, but this value is supplier-defined and must be fixed in the purchase specification. Edge wave is evaluated separately from center wave and bow. Residual stress from extrusion relaxes unevenly after slitting, so a 4.0 mm × 1,500 mm × 3,000 mm panel may show edge wave of 1.5 mm to 3.0 mm after cutting. If the incoming sheet is to be vacuum formed, the size chart must include trim allowance. Polycarbonate sheet heated to forming temperatures of 160 °C to 190 °C undergoes sag and draw. A 3.0 mm sheet with a 500 mm draw depth may require 30 mm to 60 mm blank oversize relative to the finished part. The chart’s panel size is therefore incoming stock, not the final part envelope.

When the size chart is used for cutting to finished dimensions, incoming panel tolerance must be transferred from the mill edge to the routed edge. CNC routing of polycarbonate with single-flute upcut bits at 18,000 rpm to 24,000 rpm and feed rates of 2 m/min to 5 m/min creates a kerf of 3.0 mm to 6.0 mm depending on bit diameter; the cut tolerance becomes ±0.1 mm on a well-fixtured machine. Laser cutting of thin sheet may be performed with a 150 W to 400 W CO₂ source but can introduce edge stress and yellowing if power or speed is set incorrectly. Water-jet cutting with garnet abrasive produces a clean edge without melt degradation but leaves wet abrasive residue that must be removed before bonding or hard coating. Stress relief annealing before machining at 121 °C for 1 h per 10 mm of sheet thickness reduces the risk of solvent-induced cracking on drilled holes and routed corners. After annealing, the panel is cooled slowly in the oven to below 80 °C before removal. Hard coating by dip or flow coating adds 2 µm to 8 µm dry film thickness and does not materially alter panel dimensions. The nominal thickness column in the chart therefore specifies incoming stock, not the final thickness after forming, coating, or machining.