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I am attempting to use a drill press to drill a 13mm hole in the ends of a small electronics enclosures (a Hammond case). The wall of the case is about 2mm thick and made of ABS plastic.

Started off by drilling a 5mm pilot hole and followed it up carefully and slowly with the 13mm bit. Immediately the box was grabbed by the bit and the workpiece was ruined (split down the side). After massaging my bruised thumb I realised that I need a better way to do this.

Reckon I'd have no better luck with a hand-cranked drill or a cordless drill.

My available tools are severely limited and there's no hope of getting any budget to buy new tools (not for a small project like this). I've got a decent selection of drill bits and a small, fixed-speed drill press and not much else.

I did consider just drilling a 5mm hole and simply reaming it up to the 15mm hole we actually need but this is a real pain in the neck.

What can I do to prevent this grabbing problem?

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  • Were you holding the piece with your hand? I think a rigid clamp might work. With a rigid clamp an initial very small "grab" isn't allowed to shift the piece and ramp up to a yanking grab. Also with the piece securely clamped you may be able to drill into ABS with a 13 mm hole without a pilot hole. Try it on a piece of the ruined box.
    – Jim Stewart
    Mar 22, 2017 at 10:19
  • Yes it was hand held. Having a rigid setup does sound like it would work better.
    – Wossname
    Mar 22, 2017 at 10:24
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    If you are having to drill from the outside of these boxes, so that the surface that you are drilling into cannot be clamped directly, then you could make a jig which would prevent twisting. The jig would be clamped, but the piece just dropped into it. It might be necessary to support the box internally with a wooden block.
    – Jim Stewart
    Mar 22, 2017 at 10:54
  • The boxes have their lids screwed on so the ends are actually quite rigid. They are quite small, only 120mm on the longest side.
    – Wossname
    Mar 22, 2017 at 11:00
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    I have found drilling at higher speeds, slower plunge, and firmly fixing the workpiece works pretty well for plastics.
    – whatsisname
    Mar 22, 2017 at 23:22

5 Answers 5

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Sandwich the workpiece between two pieces of wood, clamp it all together, clamp the whole assembly so that it can't go spinning off into oblivion, then drill through the whole thing. You'll also want to use really light pressure when drilling through the plastic, but don't go so slow that you melt the stuff.

If you have some, you could use a step drill instead of a twist drill.

enter image description here

If you have a bunch of in between size bits, you can simply start small and slowly work your way up to the final size. However, you're still going to want to properly brace the material. Adding support behind the piece is also a good idea.

If it's within your budget, a drill bit designed to drill plastics might work. However, you're still going to have to secure the workpiece while drilling. I'd also recommend using a wood backer, to support the piece as you drill.

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  • Yes, you're right, I should just grow up and do it properly. Actually this is for work believe it or not, we're really badly equipped for any kind of manual machining even down to this simple level. I think I'll have to take the bull by the horns and demand a tooling budget from the tyrannical overlords. Get myself a small workstation setup with a decent set of equipment. I shouldn't have to struggle with simple procedures like this. :)
    – Wossname
    Mar 22, 2017 at 11:04
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    Using the right tool for the job usually makes the job go faster with a better end result. As an argument to get budget, consider that time is expensive, and ruined parts are expensive. It's amazing how often a business will refuse to spend money on tools but then spend double that in wasted time, followed by a meeting that costs even more than that to figure out why it's taking so long...
    – gregmac
    Mar 23, 2017 at 0:59
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Considering how many times this type of question has been asked, I'm not sure why it wasn't closed as a duplication.

Reference at least one other posting: Yet another plastic drilling question

Use a drill bit made to drill plastic.

Sandwiching the material will not prevent grabbing when using a conventional bit.

The step bit may also grab and crack is used incorrectly, that is inappropriate speed for the material, but it has a much smaller chance of doing so than using a conventional steel cutting bit.

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    If you think an answer is incorrect, posting your own answer is the appropriate response. If you really have a problem with another answer, cast a down vote and leave a comment explaining what's wrong with the answer. Bashing other answers in your answer is rude, and rudeness is frowned upon around here.
    – Tester101
    Mar 23, 2017 at 0:19
  • thank you for the clarification. I will endeavor to continue in that manner.
    – fred_dot_u
    Mar 23, 2017 at 21:35
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I was going to propose using an endmill. However this requires precise positioning of the work over an existing hole (endmills can't cut in their center since it has zero velocity), which brings us back to the crux of the problem: positioning and clamping.

When I have several same workpieces, I have often built a tray by nailing scrap to a piece of plywood, that the piece drops into snug. And then clamp the tray to the drill press. If I had a CNC router handy I would just mill the tray to the piece's exact dimensions.

Feeds and speeds will be everything, otherwise it will gall or melt.

I occasionally use endmills to square the bottoms of holes in wood, as it is impossible to cut past where the drill bit tip stopped, without feeds and speeds feeling really wrong.

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Put it in a bowl of boiling water for a minute take it out and dry it and immediately drill it - it will not crack

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When I work with plastic boxes I find it best to start with a small pilot hole just like you did but I then use a hand tool that looks like the following. It works very well at shaving out the hole to the diameter needed. It is amazing how fast and easy this tool works in the thin plastic walls of a project box.

enter image description here

Some hand tools like this will come to more of a point allowing them to start in a smaller hole. The one pictured above may not be optimally pointed but does demonstrate another desirable feature. A tool with more flutes will cut a smoother round hole.

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