PC Sheet CNC Machining Parameters: Drilling, Milling, Sawing and Routing
The short version
Polycarbonate (PC) sheet machines well: standard metalworking tools do the job, preferably carbide-tipped, and the whole game is sharp cutting edges with the right geometry. What actually ruins parts is not speed or feed but three counter-intuitive rules:
- Never use cutting oils or oil-in-water emulsions — additives they contain are not compatible with PC and cause stress crack formation. Only water or oil-free compressed air is allowed.
- Withdraw the drill regularly in deep holes — this removes both heat and chips.
- Hole walls must be smooth and burr-free — any notch becomes the starting point of a crack once the fastener is tightened.
The values below follow widely used engineering practice for PC sheet machining and can be used directly as a process-card baseline.
1. Drilling parameters
| Parameter | Recommended value |
|---|---|
| Point angle | 110–130° |
| Rake angle γ | 0–5° |
| Clearance angle α | 5–15° |
| Helix angle β | 19–40° |
| Cutting speed | 15–30 m/min |
| Feed | 0.1–0.3 mm/rev |
Standard metalworking twist drills are perfectly suitable; keep the cutting edges sharp. Cooling is generally not necessary. For relatively large drilling depths, use water or oil-free compressed air and/or regularly withdraw the drill from the hole to reduce heat and remove shavings. For large-diameter holes, standard circle-cutting equipment (circle cutters, compass saws) works well.
Image source: Exolon® technical manual
2. Milling and routing parameters
| Parameter | Recommended value |
|---|---|
| Clearance angle α | 5–10° |
| Rake angle γ | 0–10° |
| Cutting speed | 100–500 m/min |
| Feed | 0.1–0.5 mm/rev |
PC sheet is easy to mill; choose the machine for the job and make sure the tool has good chip clearance and sharp cutters. For curved contours, routing is an option: a sharp tool at 20,000 rpm, using straight carbide-tipped or high-speed steel (HSS) router bits, 6–10 mm diameter preferred.
3. Sawing parameters
A circular saw is the easiest way to cut PC sheet, and carbide-tipped blades produce the cleanest cuts; tooth spacing runs fine for thin sheet to coarse for thick. Band saws suit curved cuts on formed parts and irregular shapes (wide spacing for thick material); for higher edge quality, circular saws or milling cutters beat the band saw. Below 1.5 mm thickness, use a thick underlay board or a pair of shears instead of a circular saw.
| Parameter | Band saw | Circular saw |
|---|---|---|
| Clearance angle α | 20–40° | 10–30° |
| Rake angle γ | 0–5° | 5–15° |
| Cutting speed v | 10–17 m/s | 17–50 m/s |
| Tooth spacing t | 1.5–3.5 mm | 2–10 mm |
Clear shavings off the cutting surface — they scratch the masking film and the sheet. If the cut edge goes wrong, troubleshoot in this order: a fused cut edge means check tool sharpness, reduce cutting speed, reduce the rate of advance, cool if necessary; a notched cut edge means check sharpness and tool geometry, and improve the cutting surface (add an underlay if needed).
Punching, for reference: sheets up to 3 mm cut and punch easily with a sharp shearing tool of max. 45° wedge angle and 0.01–0.03 mm clearance; for smooth cut edges on 1.5 mm and thicker sheet, saw or mill instead. If punching is followed by heat treatment above 145 °C, make punched holes approx. 5 % larger to allow for shrinkage.
4. Three details that decide whether the part cracks
- Only two coolants exist: water and oil-free compressed air. Cutting oils and emulsions cause stress cracking — no exceptions.
- Hole quality decides assembly: holes should be smooth and as free as possible of notches or rough areas to ensure secure fastening — a rough hole wall is a stress concentrator and cracks under bolt load.
- Never scribe with sharp tools: mark on the protective film with a soft pencil or felt-tip pen; a sharp tracing mark has a notching effect and the sheet may crack under load. Keep the masking film on during machining (shelf life: 6 months) and remove it immediately after installation.
One dimensional note: PC expands at 0.065 mm/m·°C, far more than metal, so always check dimensions at room temperature — one metre of sheet changes 3 mm in length over a –10 °C to +35 °C swing. See our earlier article on distortion control for the tolerance implications.
FAQ
Q: Does drilling PC sheet need coolant?
Generally not. If deep holes or continuous production cause local overheating, use water or oil-free compressed air only. Cutting oils and oil/water emulsions are prohibited — they trigger stress cracking.
Q: Why did my drilled hole crack when the bolt was tightened?
The two usual suspects: a burred or rough hole wall acting as a stress concentrator, or cutting oil/emulsion used during machining, whose additives cause stress cracking. Work through sections 1 and 4 above.
Q: The sawn edge is fused and shiny — what do I change?
Work through the checklist in order: check tool sharpness first, then reduce cutting speed, then reduce the rate of advance, and cool if necessary. For notched edges, check tool geometry and add an underlay board.
Closing
Every value above reflects widely used engineering practice and can go straight onto a process card. Wuxi Cremage Technology provides precision CNC machining of PC and acrylic sheets — drilling, milling, routing and sawing, with accuracies down to ±0.01 mm — see our industrial plastic machined parts page. Further reading: PC & acrylic distortion control, pre-drying before laser cutting and chemical resistance and stress cracking of PC.
References
- [1] Exolon® Technical Manual Solid (Makrolon® sheet, now Exolon®), Chapter 4 (Machining): https://www.exolongroup.com/index.php/fuseaction/download/lrn_file/mf0261_e_210502.pdf