I ran into a similar problem in installing rectangular keypads into plastic
boxes.  I solved the problem by mounting a router bit in my drill press.
Then I took a piece of wood and used additional strips of wood to construct
a frame on top of it (this requires some experimentation for size).  The
base piece of wood has a hole in it that is big enough for the router bit to
go through. I first drill a pilot hole in the plastic box for the router bit
to go through.   I can then put the plastic box inside the frame, install
the router bit,  and move the box around the frame along each side.  The
router bit cuts a hole with very straight sides that is the same size each
time because it uses the same frame each time.  The corners are slightly
rounded, but that just happens to fit the rounded edge of the keypads that
I'm installing.  They could be filed out into a square shape if that is
preferred.

I've probably made a thousand boxes using this one frame.  Here are some
observations:

1. I think it is nearly impossible to cut a nice looking square hole of this
size freehand.

2. There is a fair amount of setup (getting the size of the frame right)
necessary to produce the desired shape.  So if you are only doing one of
these, it may not be worth it.

3. Don't apply too much pressure when running the box around the frame.  If
you do, you can move the router bit to the side slightly and this causes the
square hole to be deformed.  You just have to be patient and let the bit do
the cutting.

4. Because I do a lot of these, I use a carbide router tip.  It lasts a long
time.

John Hansen
Coastal ChipWorks

On Sat, Feb 21, 2009 at 12:06 PM, Larry Bradley <larry.bradley@ncf.ca>wrote:

> I'm trying to find a way to cut neat rectangular holes in small plastic box
> lids for mounting LCD displays for hobby work.
>
> In the past I've drilled a series of small holes, then used a coping saw to
> cut out the piece. Then file the edges smooth. This is not very neat - the
> edges are never straight lines.
>
> When I do something like this in woodworking, I use my router to make the
> rectangular hole, then clean up the corners. But a router on a small (e.g.
> 4"x6" box) piece of plastic isn't easy.
>
> I do have a Dremel tool, but I don't have the router attachment for it -
> that
> may be an option, since it is a lot smaller.
>
> What do others out there do? Using a commercial service for a one-of box is
> probably rather expensive.
>
> Any ideas?
>
> Thanks
>
> Larry
>
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