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My electronic kit-building to date has included pre-drilled kit boxes for mounting.

My latest purchase, however, has a plastic project box, and no pre-made cutouts.

I need a rectangular hole for a small LCD screen - and I don't want to mess it up!

How best to cut the hole? Tools to use?

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    \$\begingroup\$ What ever happened to using the good ol' Dremel with a cutoff wheel? \$\endgroup\$ – Dave Feb 24 '11 at 3:54
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If the plastic isn't too thick, then you could try this:

  1. Cover the surface of the plastic with masking tape, so you don't scratch it.
  2. Mark out the rectangle you want to cut out.
  3. Using a very sharp knife, score the edges of the rectangle against the side of a metal ruler.
  4. Cut deeper and deeper grooves with the knife, until you can eventually push out the rectangle.
  5. File any rough edges, and remove the tape.
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Drill a 6mm hole and use a step drill to open it out to at least 10mm. A step drill is the best way to make large holes in thin materials, it doesn't grab as much as a large twist drill will.

Then use a 'hand nibbler' to open it out to rectangular. You can drill more large holes with the step drill to reduce the amount of nibbling required.

I made the cutouts for this project with a nibbler: LCD window cut out with nibbler

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The question is old, but I also had a lot of trouble to get this right, so it's worth answering.

  1. Draw the rectangle with a pencil or a thin felt tip pen. You can clean it later. I sometimes draw the whole panel in milimeter graph paper and tape it on the plastic box, so things are perfectly aligned and distributed. Make sure you got the measurements right.

  2. With a 1mm or smaller drill bit (you probably have one for drilling PCBs), make a hole on each corner of the rectangle. Using a ruler and the holes as a guide, draw an X across the rectangle, and make a 1mm hole on the center, where the lines intersect.

  3. With a larger drill bit, and using the 1mm hole as a guide, make the central hole big enough to fit a jigsaw blade.

  4. Using the jigsaw, carefully cut along the X lines, until you reach the 1mm holes on the corners. This will leave 4 triangles.

  5. With a very sharp knife (I use a box cutter) and a ruler, carefully make an incision along the edges of the rectangle, using the holes on the corners as a guide. You might want to always cut from the corner to the center, half at a time, to avoid damaging the opposite corner. Make the cut deeper and deeper, while pushing the triangle, until you can break it off. If you can, do it on both sides, it gives a cleaner cut.

  6. Finish with the knife and sandpaper.

It gives perfect cuts every time.

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Use a square drill bit!

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