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Thin polycarbonate is tough for its thickness, but it can still crack, melt or grab a drill bit if you treat it like plywood. For clean holes in sheet around 1–3 mm thick, a sharp standard twist bit is usually the sensible choice. The key is a controlled feed, support directly behind the hole and enough clearance for the sheet to expand around its fastener.
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Which drill bit works best?
For ordinary round holes, start with a new or sharp high-speed steel (HSS) twist drill bit. A conventional point cuts readily, is inexpensive and is easy to find in the sizes used for screws and bolts. Use it in a cordless drill with the hammer function off; an impact driver is a poor choice because its pulsing action makes it harder to control pressure and can shock the sheet.
For frequent work in plastics, a bit made for plastic can reduce grabbing. These often have a modified point with a less aggressive cutting angle. They cost more than general-purpose bits, so they are worthwhile mainly if you drill polycarbonate regularly or need cleaner holes with less hand-finishing. A brad-point bit can locate a hole accurately, but its spurs may catch thin sheet, so test it on a scrap first.
Bit choices at a glance
| Bit type | Best use | Trade-off |
|---|---|---|
| Standard HSS twist bit | Occasional holes; general-purpose drilling | Cheap and widely available, but can grab if pushed or dull |
| Plastic-point drill bit | Repeated holes and cleaner control | Costs more; unnecessary for a few careful holes |
| Step drill | Enlarging holes in thin sheet | Useful for gradual sizing, but its broad cutting edge can heat the sheet |
| Hole saw | Large openings | Requires firm support and careful speed control; not the best choice for small fastener holes |
Choose the hole size before drilling
Do not assume the hole should match the screw’s outside diameter. A screw through a fixed polycarbonate panel needs room for the sheet to move as temperature changes. Follow the panel maker’s guidance where available. As a practical starting point, a 4 mm screw often needs a hole roughly 5–6 mm wide in a panel that must expand, but the right clearance depends on panel size, mounting system and temperature range. Oversized holes may need a washer or purpose-made glazing fastener to cover them.
For an ordinary clearance hole in a small part, use the fastener’s specified clearance size. Drill a test hole in an offcut and check the fit rather than forcing a screw through a tight hole. A tight fastener can put the sheet in tension and start a crack, especially near an edge.
A reliable drilling method
Leave the protective film on while drilling if it is still clean and intact; it helps prevent scratches. Mark the location on the film, then clamp the sheet flat between scrap boards or place it on a flat sacrificial backing board. Support should reach right up to the drilling point. Unsupported sheet flexes, and the bit can snag as it breaks through.
Use a sharp bit and set the drill to a low or moderate speed. For bits around 3–6 mm, begin near 500–1,000 rpm if your drill gives a useful speed range. Keep the drill square to the sheet and use light, steady pressure. Let the cutting edges do the work. As the bit nears breakthrough, ease off further; this is when a grabbing bit can tear the exit side or lift the sheet.
Pause if the hole or bit becomes hot. Melted swarf, a rough rim or a plastic smell are signs to reduce speed or pressure and clear the chips. Don’t keep rubbing a hot bit in the hole: that makes heat without cutting. For a larger opening, a step drill is often easier to control than jumping straight to a large twist bit, but use short passes and let the sheet cool.
Avoid cracks, burrs and wandering holes
Cracks usually come from a dull or aggressive bit, excessive feed pressure, poor support, or a hole too close to an edge. Keep the center of the hole at least about two hole diameters from a free edge where the design allows, and increase that distance for larger fasteners or loaded panels. If a bit wanders on the smooth surface, make a small mark through the film with an awl or use a template; do not punch hard enough to dent the sheet.
For a small burr, carefully scrape the edge with a deburring tool or a sharp utility knife held nearly flat. Avoid countersinking unless the fastener system calls for it: countersinks remove material and can create a stress point in thin plastic. Don’t use a high-speed grinder to clean the hole, since it can melt the rim.
What to buy for the job
If you only need a few holes, a sharp, inexpensive HSS twist bit set is fine. Choose one that includes the exact sizes you need rather than a large assortment of poor-quality bits. If you routinely drill plastic or need consistent results across many panels, consider a plastic-cutting drill bit set. For occasional large holes, a step bit can be more useful than buying several large twist bits.
Whatever the bit, the drill matters less than control. A standard cordless drill on its lowest gear is adequate; disable hammer mode, avoid impact tools, clamp the sheet, and let the bit cut without forcing it. That approach is usually enough to get a clean hole without buying specialty equipment.