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What kind of bit should I use to drill a 1/2" hole into acrylic glass (plexiglass)? The local hardware store does not have a 1/2" hole saw - which was my first inclination. I am now considering these options in the following order:

  • Spade bit
  • Forstner bit
  • 1/2" straight drill bit
  • Step-up from small (3/16") to 1/2" straight bit
  • Knock-out/Step-up bit
  • 1/2" Diamond plug cutters (expensive)

I'm thinking the spade bit may work but will leave a rough surface (which I can sand) and will give me less control than a forstner bit. Starting with small straight bits and stepping-up to 1/2" seems safe but time consuming.

Luke1018
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3 Answers3

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If you have access to a laser cutter, e.g. local makerspace or hackerspace, community college, or public library that might have a "fab lab", then that is the approach I would suggest. EX: https://www.youtube.com/watch?v=yjwOC26OJFU

AA040371
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You do not specify thickness, so I'll take a guess at 1/4" or thinner.

The problem with drilling plastic is that conventional bits will "catch" on the plastic, pulling the bit into the hole with more force than desired, typically cracking the plastic being drilled.

Using step-up method to drill the hole will not eliminate this problem.

Lacking the aforementioned hole saw, the spade bit is a better choice. I have Forstner bits but have not considered trying one on plexiglass. If you have a drill press and the increased control it offers, you may have good luck taking small bites with the forstner. The cutting edge of a forstner bit is more like the edge of a plane and may also dig in too quickly otherwise.

Drill bits designed for plastic have a much sharper angle. A set I recently purchased has an abrasive material on the cutting surface as well as a subdued cutting angle, effectively abrading the plastic and lifting it to the surface.

I overlooked your option of a step drill which is the best of the list. Each progressive cutting edge will not gouge into the plastic as much as any of the other available choices. Again, a drill press improves your chances of a good result.

fred_dot_u
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to drill a hole in plexi, you can use a standard fluted twist drill, but you have to grind the cutting edge. you have to grind the edge flat, in relation to the rotational axis. imagine if you held a file parallel to the long axis of the drill and filed the edge of the cutting flute down. this breaking of the edge helps to prevent the bit from pulling through as the bit exits the workpiece. the softer the plastic, the more you have to flatten the edge. plexi is pretty brittle, so you can just file it until the edge is .010"-.020" on the flat.

you will want to use a pilot hole, say 1/4" first. just ease the cutting edge the same way as above.

when you drill, flush the hole with water to lubricate and cool. don't use oil, silicone or any solvent as it can cause crazing of the hole.

personal privacy advocate
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