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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.

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    I would not use a spade on plastic sheeting. 1/2" hole saw would be the best option have you checked on line, I think door locks are 1/2" and those kits have both size cutters. – Ed Beal Jan 19 '18 at 19:45
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    How thick is plastic? You'll get through with a Forstner, but will likely end up with melted plastic flashing you'll need to remove carefully. Clamp the plastic down firmly, with wood underneath. Plexiglass is very good at jamming on bit and trying to fly across room. – Wayfaring Stranger Jun 29 '18 at 1:02
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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.

  • A guy at Lowes told the cut plastic with a power chop saw you should put the blade on to spin in the opposite direction. It worked well. Maybe if you put the drill in reverse to drill plastic it would mitigate the catching problem. – Francis Aug 31 '16 at 3:40
  • considering that the aforementioned plastic cutting drills are barely more than sandpaper tips, your suggestion appears quite sound. There would be substantial melting, I think, but it's something I'm going to check out one day. – fred_dot_u Aug 31 '16 at 9:35
  • I agree that a step bit may be the best for the application, though the sheet may be too thick for the bit. – Jonathan J Sep 1 '16 at 6:20
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    You can use a standard, fluted bit, IFF you sandwich the plexiglass between some sacrificial wood, like 2x4s. Clamp tight and drill away. – BrownRedHawk Sep 29 '16 at 13:24
  • BrownRedHawk, making a sandwich with thin enough plexiglass may work, but if the point catches on the plastic and pulls the bit faster than it is cutting, the plastic will crack at the hole. Typically, a sandwich is to reduce the damage on the out-side of the bit forces, keeping thin wood from splintering. – fred_dot_u Feb 7 '17 at 1:08
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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

  • To whomever down-voted this answer, it's a little ridiculous to do so without explaining why. – mblatz01 Aug 31 '17 at 16:27
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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.

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