Recommendations for Drilling Acrylic and Polycarbonate Sheet

                                          
                                                                     By Jim Hingst 

@hingst_jim

Drillbits for plastics, such as acrylic sheets and polycarbonate sheets, are significantly different than those used for drilling wood or metal. Using the wrong type of drill bit can result in the tool grabbing as you are drilling, which can lead to chipping at the edge of the hole. That’s a real problem because chips can propagate into cracks. According to Alison Svoboda of Boda Corporation, "polycarbonate  is "notch sensitive" so a sharp drill bit is imperative. Even a small hairline fracture will result in a crack at some point."  (Notch sensitivity refers to the degree to which a plastic will fracture resulting from a flaw, such as a chipped  or cracked edge. Cf. Test Methods: Mechanical Properties of Plastics.)

Which Drill Bits are Recommended

One difference between the types of drill bits is the angle of the tip. A standard drill bit typically is at flat 120° angle. For drilling acrylic sheet and polycarbonate sheet, you need a drill bit with a sharp point, generally at a 60° angle. 

The back relief angle of the cutting edge ensures that the drill bit designed for plastic shaves slivers of material rather carving away large chips that could propagate cracks.

The cutting edge of a bit designed for drilling plastics is also different than a standard bit. The back relief angle of the cutting edge should be ground away at a 10° to 15°. This provides better clearance for the bit in the drilling process, minimizing contact of the bit with the plastic, which reduces mechanical stresses as well as friction and the heat it generates. 

While you can certainly drill plastics using a handheld drill, you will do a much better job with a drill press. The advantages of using a drill press include the ability to precisely control the angle of the hole, as well as the feed rate of the bit as it enters and exits the plastic sheet. A slow feed rate helps reduce the incidence of chipping. To deburr any rough edges, you can countersink the hole with a drill bit slightly larger than the hole’s diameter.

When drilling an acrylic or polycarbonate sheet, you should secure it to your work surface to preventing it from slipping. You should also back up the plastic piece with a scrap of plywood or MDO. The scrap sheet of material relieves any pressure on the plastic, which minimizes chipping and cracking. 

Clamp the plastic onto a scrap piece of MDO or plywood. Then drill the pilot holes.  

Which Drill Speed is Recommended for Plastics

As a general rule of thumb, the recommended speed of the drill should be reduced as the size of the hole drilled increases. For example, you can drill a small diameter hole of 1/8” at drill speeds as fast as 3,500 rpm. However, when you are drilling a ¼” hole, the recommended speed of the drill should be reduced to 1,800 rpm. 1” holes should be drilled no faster than 450 rpm. To prevent cracking, holes should not be drilled at a distance closer to the edge of the sheet less than 1-½ times the diameter of the hole itself.  

Drilling Procedures

When drilling larger holes in a thicker piece of plastic, you will need to take additional precautions. These measures include drilling a pilot hole first. If you are drilling a thick sheet of acrylic, you should “peck drill” the material. What this means is to drill a little of the hole at a time, repeatedly removing the bit from the hole to extract the shavings. Not only does this practice prevent the accumulation of debris resulting in the drill bit from binding in the hole, but it also avoids the build-up of heat and melting of the plastic.

If you are drilling through several sheets of plastic, you will most likely need to use some type of coolant, such as water, to dissipate the heat that will build up. The lubricant will also help expel any of the plastic chips from the hole as you are drilling. What’s more, use of a lubricant will result in a smoother finish of the hole.

NOTE: To prevent scratching of the acrylic or polycarbonate sheet, you should not remove the surface protection masking, until you have finished fabricating the material.

Do not remove the surface protection masking prior to fabrication. Paper and film masking prevent damage to the sheet. Both types of masking allow you to draw on the surface as you lay out your job.  

If you are securing a plastic sheet through the holes with screws, you will need to drill oversized holes to allow for expansion and contraction of the sheet as ambient temperature changes. Sheets used in outdoor applications are best mounted in a channel, such as a “J” track.

SAFETY NOTE: When fabricating acrylic sheet and polycarbonate sheet, always read the manufacturer’s instructions and follow the recommended safety guidelines, such as wearing safety goggles. 

About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 400 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.  Vinyl Sign Techniques is available at sign supply distributors and at Amazon. 

Slides of Jim's Artwork

© 2016 Jim Hingst