Can you screw into acrylic?

Key facts

• Hole type: a clearance hole bigger than the screw, not a pilot hole smaller than it.
• Head style: pan, round, truss, or washer heads with a flat underside. Plaskolite says to avoid flat and oval (countersunk) heads, which create hoop stress.
• Hole size for moving panels: Acrylite recommends a bolt hole at least twice the bolt diameter where the sheet needs room to expand.
• Edge distance: at least twice the hole diameter, and twice the sheet thickness, from hole to edge (Plaskolite).
• If you must self-tap: thread-cutting screws (ANSI Type 23 or Type 25), not thread-forming screws, and still expect a crack risk with temperature swings.
• No threadlocker: Plaskolite lists it as incompatible with acrylic.

Why do screws crack acrylic?

Wood and sheet-metal screws work by forcing their threads into the material. Wood fibers compress and grip; acrylic doesn't compress. It's stiff and brittle, so a screw forced into it pushes the plastic outward until it cracks. The crack may not show right away. Plaskolite notes that cracks can form around screw holes as the acrylic expands and contracts with temperature, and acrylic moves about four times as much as metal. A screw that was snug in winter is wedged tight in summer.

Screwing into the edge of acrylic sheet is the worst case. There's little material on either side, and the sheet splits along the face.

Five ways to fasten acrylic that work

1. Clearance holes with washers

The standard method for panels, covers, and signs. Drill or cut a hole in the acrylic larger than the screw so the screw passes freely through it and only threads into the wall, frame, or stud behind. Then:

• For small indoor parts, about 1/16 in. over the screw diameter is usually enough. For large or outdoor panels, Acrylite's guide is a hole at least twice the bolt diameter, or slot the holes along the long direction (expansion calculator).
• Use pan-head, truss-head, or washer-head screws, with a flat washer under the head. Plaskolite suggests flat aluminum or hard plastic washers to spread the force; rubber or nylon washers add cushion.
• Tighten until snug and stop. The acrylic should be held, not clamped hard.
• Keep holes at least twice their diameter, and twice the sheet thickness, from the edge.

2. Standoffs

Sign standoffs are metal barrels that hold a panel off the wall with a cap screwed through a hole in the acrylic. They look clean, hide the screw, and clamp the panel without wedging it. Plaskolite's guide also points to standoffs and spacers for mounting. They're the usual way to mount a sign or nameplate. See acrylic signs with standoffs.

3. Threaded inserts

Brass heat-set, ultrasonic, or epoxy-bonded inserts in thick acrylic give you real, reusable metal threads. They're the right choice when a machine screw goes in and out repeatedly, like a removable cover. Use the insert maker's hole size: undersized holes stress and crack the plastic.

4. Tapped holes

In 1/4 in. and thicker acrylic you can cut threads for machine screws (not wood screws). Coarse threads and light torque are the rules. See how to tap threads in acrylic.

5. Bolts and nuts

For acrylic-to-acrylic or acrylic-to-metal joints, a bolt through clearance holes with a washer on each side and a nut is the strongest option. Use nylon-insert lock nuts rather than threadlocker. Where acrylic meets metal, Plaskolite recommends a rubber or cork gasket between them.

What size hole for a screw in acrylic?

Not a pilot hole. A pilot is meant to be smaller than the screw, which is exactly what cracks acrylic. You want a clearance hole larger than the screw's outside thread diameter, plus room for movement:

The free-fit sizes come from a standard machinist's clearance chart. Go bigger, or slot the holes, for long panels and anything outdoors.

Are there screws made for plastic?

Yes, but read the type. Thread-forming screws push plastic aside to make their thread, which puts acrylic in hoop stress. Thread-cutting screws (ANSI Type 23 and Type 25, or Hi-Lo style) cut away material in a pre-drilled hole, and Plaskolite says they leave lower stress and perform better long-term. Even so, the same guide warns they may not suit every application, because cracks can form around the hole with temperature changes. For anything that matters, clearance holes, inserts, or tapped holes are more reliable.

Can you countersink acrylic?

Carefully, and only in thick sheet. A flat-head screw is a cone, so as it tightens it pushes outward on the acrylic. Plaskolite advises against countersunk screws in acrylic for exactly that reason. If you need a flush head:

• Use 1/4 in. or thicker acrylic.
• Make the countersink slightly deeper and wider than the head, so the head seats lightly instead of wedging.
• Use a machine screw or a screw with a finishing washer through a clearance hole.
• Tighten gently.

In thinner sheet, use pan-head screws with washers or standoffs instead.

Gluing as an alternative

Sometimes the best fastener is no fastener. Acrylic bonds to itself with solvent cement and to other materials with the right adhesive. See how to glue acrylic to wood, metal, and glass, and how to mount acrylic to a wall.

Let us make the holes

Holes cut by laser or drilled in our shop are round, clean, and free of the chips that start cracks. We can countersink and tap them too (tapped holes need 1/4 in. or thicker). Add holes to your part in the instant quote.

Questions

Sources

• Plaskolite: OPTIX acrylic sheet fabrication guide (mechanical fastening)
• Plaskolite: OPTIX-L continuous cast acrylic sheet fabrication guide (mechanical joining)
• Acrylite: Drilling ACRYLITE acrylic sheet
• East Tennessee State University: Tap drill and clearance hole size chart
• SPIROL: Threaded inserts for plastics design guide