Acrylic cracks when drilled with standard techniques, but using a step drill bit at 1,000–1,500 RPM with water cooling prevents heat buildup and delivers clean holes every time.
How to drill acrylic without cracking comes down to three things: the right bit, the right speed, and keeping it cool.
The Right Way to Drill Acrylic Without Cracking
Pick the correct drill bit. Standard twist bits grab and fracture acrylic. For tested recommendations, see the best drill bits for acrylic.
Leave the protective masking film on to prevent scratching. Mark the hole with a grease pencil on the film, then add a strip of masking tape over the mark for an extra barrier. Ensure the hole sits at least 1.5 times its diameter from any edge to stop stress cracks.
Clamp the sheet firmly to a flat wooden backing board — never hold it in your hands. Set your drill to 1,000–1,500 RPM. Start with a 3 mm pilot hole using a brad-point or modified twist bit to guide the larger bit and spread stress evenly. Apply gentle, steady pressure. For sheets thicker than 5 mm, pause every few seconds to spray water into the hole or use WD-40, which leaves the cut clear. Just before breakthrough, reduce feed pressure to prevent chipping. Per Plexiglas’s official drilling guide, this is one of the most important steps. After drilling, deburr both sides with a countersink bit or fine sandpaper.
Why Does Acrylic Crack During Drilling?
Heat is the number one cause. High speed generates friction that melts acrylic, and the melted material expands and cracks as it cools. Drilling without a backing board lets the sheet flex and fracture. An unmodified twist bit grabs and jerks, sending stress cracks through the material. Drilling too close to an edge concentrates force. Pushing too hard creates heat buildup and oversized holes.
Common Acrylic Drilling Mistakes to Avoid
| Mistake | What Happens | Fix |
|---|---|---|
| High RPM | Melting and cracking from friction heat | Keep speed at 1,000–1,500 RPM |
| No backing board | Sheet flexes; rough, chipped exit hole | Clamp to a flat wood surface |
| Hole too close to edge | Edge cracks from stress concentration | Maintain 1.5× diameter distance |
| Heavy feed pressure | Heat buildup, oversized hole, cracking | Use gentle, steady pressure |
| No cooling or lubrication | Thermal expansion, melted shavings | Use water or WD-40 regularly |
| Unmodified twist bit | Bit grabs and fractures the material | Use a step bit or modified bit |
| Fast punch-through | Blowout and chipping on back side | Slow feed pressure before exit |
FAQs
Can I use a regular drill bit for acrylic?
Do I need to lubricate when drilling acrylic?
Water works well.
Why does my acrylic keep cracking no matter what I try?
References & Sources
- Plexiglas. “Drilling Plexiglas.” Official manufacturer guide covering bit selection, speed, and technique for clean holes in acrylic.
- SFBaySigns. “Drilling Holes in Acrylic Signs.” Professional sign fabricator’s practical field guide to drilling without cracking.
- Wee Tect. “Drilling Acrylic.” Expert overview of common mistakes and tested solutions for DIY and professional use.