How to Drill Holes in Acrylic Signs Without Cracking

Drilling holes in acrylic signs seems straightforward—until you end up with a cracked mess. Acrylic (also called plexiglass or Perspex) is a popular material for custom acrylic signs because it looks sleek and professional, but it requires specific drilling techniques to avoid damage.

This guide covers everything you need to know about drilling clean mounting holes in acrylic signs, from choosing the right drill bit to finishing the holes properly.

Why does acrylic crack when drilled?

Acrylic cracks during drilling primarily because of heat buildup. Friction from the drill bit generates heat, and acrylic expands when heated. This thermal expansion creates internal stress that results in cracks radiating from the hole.

The other major cause is using the wrong drill bit. Standard twist drill bits have cutting angles designed for metal, which catch and grab acrylic rather than cutting cleanly. This grabbing action creates mechanical stress that causes the material to fracture.

What tools do you need to drill acrylic?

Successful acrylic drilling requires the right equipment. Here is what professional sign shops use:

• Drill bits for plastic: Specially ground bits with modified cutting angles that scrape rather than cut. Röhm, the manufacturer of PLEXIGLAS®, recommends spiral bits with geometry specifically designed for acrylic.
• Brad point bits: An alternative that centers easily and cuts cleanly in acrylic.
• Step drill bits: Excellent for thin sheets; create clean, score-free holes.
• Clamps: Secure the acrylic to a flat wooden base to prevent movement.
• Masking tape: Apply over drill points for extra crack protection.
• Spray bottle with water: For cooling during drilling.
• Safety glasses: Acrylic chips can be sharp.
• Fine sandpaper or countersink: For deburring finished holes.

How do you drill acrylic without cracking it?

Follow this step-by-step process used by professional sign fabricators:

Step 1: Keep the masking film on

Do not remove the protective film from your acrylic sheet before drilling. This film provides an extra layer of protection against surface scratching and helps prevent chipping around the hole.

Step 2: Mark your hole locations

Use a permanent marker or grease pencil to mark exact drilling points on the masking film. Double-check measurements before drilling—maintaining at least 1.5× the hole diameter from any edge prevents edge cracking.

Step 3: Secure the acrylic sheet

Clamp the acrylic to a flat wooden base. The backing support prevents the material from flexing during drilling and provides a clean exit for the drill bit. Never drill acrylic while holding it in your hands.

Step 4: Apply masking tape over drill points

Even with the protective film in place, adding masking tape over drill points provides an extra barrier that reduces the risk of surface tearing.

Step 5: Start with a pilot hole

Begin with a small pilot hole (about 3mm) before drilling your final size. This starter hole guides the larger bit and distributes stress more evenly, significantly reducing crack risk.

Step 6: Use low speed and gentle pressure

Set your drill to a low speed setting. As a general rule, larger holes require slower speeds. Let the drill do the work—pressing hard generates heat and causes cracks. The ideal drilling produces smooth, continuous shavings rather than crumbly chips or melted material.

Step 7: Cool and clear debris periodically

For sheets thicker than 5mm, pause periodically to spray water into the hole and clear accumulated shavings. Heat buildup is the primary cause of drilling failures, and cooling prevents it.

Step 8: Slow down before breakthrough

Reduce feed pressure just before the drill exits the back side. This prevents chipping and blowout on the exit side of the hole.

Step 9: Deburr the holes

Use a countersink or fine sandpaper to smooth both sides of each hole. This removes sharp edges and small notches that can become stress points over time.

Cast vs. extruded acrylic: Does it matter for drilling?

Yes. Cast acrylic is more forgiving during drilling—it machines more predictably and is less prone to cracking. Extruded acrylic costs less but has internal stresses from the manufacturing process that make it more susceptible to cracking during drilling.

If you are drilling mounting holes in signs that need to look professional, cast acrylic is worth the extra cost. For test pieces or less critical applications, extruded acrylic works with extra care.

Common mistakes that crack acrylic signs

Avoid these frequent errors:

• Using standard metal twist bits: Their aggressive cutting angles catch and crack acrylic.
• Drilling too fast: High RPM generates heat that causes thermal cracking.
• Applying too much pressure: Let the bit cut at its own pace.
• Skipping the pilot hole: Starting with your final size bit increases crack risk significantly.
• Drilling too close to edges: Keep holes at least 1.5× the diameter away from edges.
• Drilling unsupported material: Always back acrylic with a solid surface.

When to let professionals handle it

While drilling a few mounting holes is manageable as a DIY project, certain situations benefit from professional fabrication:

• Large signs requiring multiple precisely aligned holes
• Thick acrylic (over 10mm) that requires specialized equipment
• Signs where crack-free results are critical for appearance
• Projects requiring countersunk or threaded holes

Our shop handles acrylic sign fabrication and professional installation for Bay Area businesses. If you need mounting holes drilled with precision, we can include that in your sign order.

Ready to create your acrylic sign?

Whether you are drilling mounting holes yourself or need professionally fabricated acrylic signage, we can help. Start your project with SF Bay Signs and get expert guidance on materials, mounting options, and installation.

FAQ

What drill bit works best for acrylic signs?

Specially ground plastic drill bits or brad point bits work best. Standard twist bits have aggressive angles that catch and crack acrylic. High-speed steel bits designed for plastic scrape rather than cut, which prevents stress fractures.

Why does my acrylic crack when I drill it?

Cracking usually happens from too much speed, too much pressure, or using the wrong bit. Drilling generates heat through friction, and acrylic expands when heated. This thermal stress causes cracks. Slow speed, gentle pressure, and proper bits prevent this.

Should I use water to cool acrylic while drilling?

Yes, especially for thicker sheets (over 5mm). Water cooling prevents heat buildup that causes cracking. Use a spray bottle to apply water to the drill hole periodically during drilling.

Can I use a regular hand drill for acrylic?

Yes, a standard power drill works fine. The key is using the right bit and keeping speed low. A drill press provides more control but is not required for most sign mounting holes.

How close to the edge can I drill in acrylic?

Keep holes at least 1.5 times the hole diameter away from any edge. For example, a 6mm hole should be at least 9mm from the edge. Drilling too close causes edge chipping and stress cracks.