Well, I have no idea how to optimize it, but I'm building an airplane from a
kit and have had to cut a bunch of lightening holes in aluminum.

They are always as large as possible, with the edges of the holes going to
within about 10-15% of the edge of the part, with similar amount of material
between the  holes.

As I understand it, the loss of hardness around the hole is a plus because
it helps to release stress concentrations.

The airplane instructions stress again and again that it is necessary to
make sure that the edges of all holes be very smooth, as any nicks, gouges
or sharp edges will create stress concentrations which can initiate
cracking.

> -----Original Message-----
> From: Roman Black [mailto:fastvid@EZY.NET.AU]
> Sent: Monday, October 15, 2001 10:07 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Drilling a square tube??
>
>
> Hi, I know this is more of a mech engineering
> question than an EE one, but here goes. :o)
>
> I need to drill a square tube, hardened aluminium,
> to make it as LIGHT as possible. The square tube
> is 25mm across each edge, and used on a racing
> motorcycle for a non-critical purpose, ie it's
> not part of the drivechain!! It's about 1.2mm
> thickness wall (25mm x 25mm x 1.2mm) if that
> helps.
>
> From my rather "fuzzy logic" examination of the
> stucture the square tubing is not stressed under
> flexion, but it will be exposed to compression
> and expansion forces, so there is nothing to bend
> it, but it needs good strength for compressing
> and stretching forces... ;o)
>
> I'm not after formulae as the problem is slightly
> more complex than what I have posted, but any
> general ground rules and "reasons why" will be
> really appreciated.
>
> Do we drill the tubing with large diameter
> holes, or lots of small holes, and why/how
> will each method give the BEST STRENGTH for
> the MAX amount of weight lost???
>
> Thanks guys! :o)
> -Roman
>
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