Drilling Plastic

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Revision as of 13:06, 23 September 2011 by Eburdick (talk | contribs) (Cooling and Lubrication)

Special Scraping Drill Bits

Using a regular twist drill in plastic is a problem because the cutting edge takes too big a bite on each rotation of the drill. The best way to drill plastic is with special drill bits designed for plastic. These bits use a scraping action instead of slicing into the material, and they have a much more acute angle on the tip so that the hole is more gradually enlarged than with a metal cutting 118 or 135 degree bit. One brand is "Plexi Point," shown below.

Plexi point drills.jpg

Regular high speed drill bits can be ground to cut plastic. See this site for details.

Hole Saws

You can cut plastic with a hole saw, but the balance between enough force to cut and enough to melt the plastic is fine.

Step drills

Step drills are good both for sheet metals and plastics. A step drill starts with a small hole and sequentially enlarges it in small step with a single cutting edge until the desired size is reached. Different drills have different step sizes to handle different thicknesses of material. Some drills have a spiral flute, which improves the removal of waste.

Step drill1.jpg Step drill2.jpg


Zero Flute Countersinks

We have had some success with enlarging holes using a zero flute countersink and cutting all the way through. The single cutting edge on these countersinks is not really scraping, but takes a controlled fine cut on each rotation.

Zero flute contersink.jpg

I'm Melting!

Cooling and Lubrication

The most common "gotcha" when cutting plastic is most plastics melt when they get only moderately hot. And it is hard to avoid its getting hot with all of the friction involved with drilling and cutting. Though it can get messy, water is a good lubricant and coolant for cutting plastic.

Time vs Pressure

With practice, you can learn to feed a drill or saw at the right compromise speed to avoid melting from friction. Feeding too fast generates more friction, and can jam melted plastic into saw teeth or drill spiral, causing even more friction. It is important for chips to fly clear so they don't contribute the this friction. On the other hand, hesitating to the point of not cutting fast enough will also build up heat.

Peck Drilling

One way to reduce the problem of melting is to make the cut with a series of short feeds instead of one long feed, giving the tool and work a chance to cool with the tool out of contact with the work between "pecks." This works well for drilling or sawing.

Backing up the Work

When a cutter, whether a drill or a saw, finishes its cut and leaves the plastic (break through,) there are a lot of forces pushing out the back side, which can cause chipping and cracking. It is very helpful to have a scrap of wood or plastic in contact with (clamped to) the back side of the work so that the break through happens on a material you don't care about.