How to Drill Acrylic Without Cracking It: Practical Guidelines for Clean Holes

Key Takeaway

Acrylic (PMMA) can be drilled cleanly when the sheet is fully supported, a bit with a 60–90° point angle and low rake is used, rotational speed stays moderate, feed pressure remains light and steady, and heat is managed by chip clearing or intermittent cooling. Cracking is most often caused by unsupported exit, aggressive bit geometry that grabs, excessive speed that generates heat, or high force near breakthrough. Results vary with sheet thickness, grade (cast vs. extruded), hole diameter, and equipment control, so test the exact combination on scrap of the same material before committing to finished parts.

Why Acrylic Cracks When Drilled

Acrylic is a thermoplastic that softens under frictional heat and can develop stress concentrations when a bit grabs or the unsupported sheet flexes at exit. Standard metal-working twist bits typically have steeper point angles (often around 118°) and positive rake that cut aggressively; on acrylic these can cause chipping on entry/exit or melting that re-solidifies into rough, stressed holes. Vibration from loose clamping or lack of backing material amplifies the problem, especially on thinner sheets. Leaving the protective masking film in place and clamping firmly over a sacrificial backing board (wood, MDF, or another acrylic sheet) addresses the most common mechanical causes.

Tools and Bit Selection

A variable-speed drill or drill press is preferable so speed can be adjusted. Plastic-specific or acrylic-modified bits are recommended; these are commonly ground with a 60–90° point angle and near-zero rake so the bit scrapes rather than gouges. Manufacturer guidance (for example ACRYLITE fabrication notes) indicates that a 90° tip works well for many operations while a 60° tip is often preferred for larger diameters (around ½ inch / 12–13 mm and above). Standard HSS bits can be used after regrinding the point and rake, but unmodified sharp metal bits increase the risk of grabbing.

Common Bit Options for Acrylic
Bit Type	Typical Suitability	Notes
Plastic / acrylic-specific (60–90° point, low rake)	Preferred for most thicknesses	Designed to shear cleanly; reduces grabbing and exit chipping when sharp and properly supported.
Modified HSS twist (re-ground 60–90° point, ~0° rake)	Acceptable with care	Requires proper regrind and testing; clearance angles behind the cutting edge help reduce heat.
Step / unibit-style	Useful on thinner sheets	Gradual enlargement reduces stress; needs solid backing. Less ideal for deep holes in thick material.
Brad-point / spur-point	Possible on thin-to-medium sheet	Center point helps location; results depend on sharpness and support.
Unmodified standard metal twist (steep point)	Higher risk	More likely to grab, chip, or generate excess heat.

Always verify the bit is sharp. Dull bits rub, generate heat, and increase melting or crazing risk.

Speed and Feed Starting Ranges

Exact RPM and feed depend on hole diameter, sheet thickness, bit geometry, and whether the operation is manual or CNC. Larger diameters and thicker material generally benefit from lower RPM to limit heat. The ranges below are commonly cited starting points drawn from fabrication guidance and shop practice; they are not universal guarantees and should be adjusted based on chip appearance and surface quality. Clean continuous chips and a smooth hole wall indicate better conditions; melted residue or crumbly chips signal the need to change speed or feed.

Approximate Starting RPM Ranges by Thickness (Manual / Drill-Press Context)
Approximate Thickness	Common Starting RPM Range	Additional Notes
Up to ~3 mm (thin)	1,000–1,500	Higher end possible with small bits and solid support; reduce pressure near exit. Flexing risk is higher.
~3–6 mm	750–1,200	Moderate speeds with light steady feed; intermittent chip clearing helpful.
~6–12 mm	500–900	Peck drilling and cooling become more important as depth increases.
Over ~12 mm	300–700	Lower speeds, frequent pecking, and coolant (air or compatible liquid) recommended for deeper holes.

Larger hole diameters within any thickness usually call for the lower end of the range because peripheral speed is higher. Feed should be light and consistent; excessive force raises mechanical stress, while too little feed can cause rubbing and heat. For holes deeper than the bit diameter, peck (withdraw periodically) to clear chips. Manufacturer data (such as ACRYLITE SFM/IPR tables) can be used to calculate more precise settings when diameter and equipment allow.

Edge clearance also matters. Guidance from acrylic manufacturers often recommends locating hole centers at least roughly 1.5 times the finished hole diameter from the sheet edge for point-fastened applications, and keeping the hole diameter itself larger than the fastener to allow for thermal movement. Many fabricators aim for a practical minimum of about 15 mm or 1–2× thickness from edges on ordinary sheet work to reduce crack initiation risk.

Step-by-Step Process

Leave protective film on if possible. Mark hole centers accurately (masking tape can help prevent surface scratches).
Place the sheet on a flat sacrificial backing board (wood, MDF, or scrap acrylic) and clamp both securely so the sheet cannot flex or vibrate.
Select or prepare a suitable bit. Start the drill at the chosen speed before contacting the material.
Enter with light pressure. Maintain a steady, moderate feed that produces clean chips rather than forcing the bit.
For thicker material or deeper holes, peck: advance a short distance, withdraw fully to clear chips, and allow brief cooling. A light mist of water, soapy water, or compressed air can help when depth exceeds bit diameter or when multiple holes are drilled.
Reduce feed pressure as the bit approaches breakthrough so the backing supports the exit face and prevents blow-out.
Withdraw the bit while still rotating. Deburr carefully with light pressure (a zero-flute countersink or appropriate tool) if needed for fastener clearance or appearance.
Inspect the hole and surrounding area on scrap first, then proceed to the finished part.

Scenario-Based Recommendations

Thin sheets for retail displays, signage, or light fixtures (typically under ~6 mm)

Support and exit control matter most. Solid backing, clamping, and reduced pressure near breakthrough usually prevent cracking even with modest speeds. Step bits can be convenient for a range of small holes. Pilot holes are helpful when final diameters exceed roughly 6–8 mm.

Medium-thickness panels for boxes, trays, or organizers (~6–12 mm)

Combine moderate RPM, peck drilling, and intermittent cooling. Keep holes well clear of edges. After drilling, light edge finishing or polishing (if required for appearance) is easier when the hole wall is already clean.

Thicker stock or acrylic blocks

Lower speeds, frequent pecking, and reliable cooling become more important. Heat buildup is the primary risk. For precision or repeated holes, CNC machining or professional fabrication often produces more consistent results than hand drilling.

Large-diameter holes

Pilot drill first, then enlarge with a step bit or appropriately modified larger bit / hole saw at low speed. Circle cutters or fly cutters (used only in a drill press with firm clamping) are sometimes employed for diameters over about 25 mm; coolant and slow feed are essential. Never use a circle cutter in a handheld drill.

Common Mistakes to Avoid

Drilling without a backing board or with insufficient clamping.
Using an unmodified aggressive metal bit at high speed.
Applying heavy force to “push through.”
Failing to clear chips on deeper holes, leading to melting and re-welding.
Placing holes too close to edges.
Skipping a test hole on identical scrap material.

When Professional Fabrication Is Preferable

For production quantities, tight tolerances, complex shapes, polished edges, or parts that will be assembled into retail displays, boxes, or fixtures, controlled CNC or laser cutting followed by professional finishing usually yields more consistent results than manual drilling. Custom-Displays.com (operated by Sunday Knight Co., Ltd., Dongguan, China) provides custom acrylic fabrication services including precision cutting and machining for displays, boxes, blocks, and related retail solutions. Relevant pages include the acrylic cutting service, the products overview, and custom solid acrylic blocks. The company has supplied custom acrylic projects since 2012; manufacturing processes are selected according to design, thickness, finish, and application requirements.

General acrylic knowledge in this article is independent of any specific supplier. Customers seeking fabricated parts can submit drawings, dimensions, or reference images for review.

FAQ

What is the single most effective step to prevent cracking?

Fully support the sheet on a sacrificial backing board and clamp it so it cannot flex, then reduce feed pressure as the bit exits. This combination addresses the most frequent cause of exit chipping and cracking.

Can I use a regular twist bit?

Only after modifying the point angle to the 60–90° range and reducing rake so the bit scrapes rather than grabs. Unmodified bits raise the risk of grabbing and exit damage. Plastic-specific bits are simpler for most users.

Do I need coolant?

Not always on thin sheet with short holes. Coolant (air blast, water mist, or compatible lubricant) is advisable when hole depth exceeds bit diameter, for larger diameters, or when drilling multiple holes in succession, because heat accumulation is the main contributor to melting and residual stress.

How far should holes be from the edge?

A practical minimum is often around 15 mm or roughly 1–2 times the sheet thickness for ordinary work. For point-fastened applications, manufacturer guidance commonly suggests hole-center distance of at least 1.5 times the drilled-hole diameter, with the hole itself oversized relative to the fastener to allow thermal movement.

Is cast acrylic easier to drill than extruded?

Both can be drilled successfully with proper technique. Cast sheet is often preferred for optical clarity and machining response in display applications, but thickness, support, bit condition, and heat management remain the dominant factors. Test the specific grade and thickness being used.

About the Author

Linda Qu is Customer Service Manager at Custom-Displays.com. She has more than 15 years of experience supporting acrylic fabrication projects and has coordinated over 3,000 custom acrylic orders shipped to customers in more than 30 countries. The technical guidelines above reflect standard fabrication practices for PMMA sheet and are presented separately from company service information.

References

ACRYLITE® Drilling Guidelines (bit geometry, support, SFM/IPR considerations, coolant, edge clearance).
General fabrication practices summarized from multiple acrylic sheet manufacturer technical notes on plastic drilling (point angles typically 60–90°, backing support, peck drilling for deeper holes).

These references are provided for technical context. No competitor commercial sites are cited.