Teardrop shaped holes: structural or flourish?

I'm taking a close look at the Mendel pieces in an attempt to see how many I can make from sources other than a reprap. I noticed that there are several pieces with holes shaped like a teardrop (see x-180-z-bearing-plate_2off.stl for an example).

Do these special shape of hole have a structural purpose? They're probably going to be pretty difficult to produce to any degree of accuracy using a drillpress.

Or are these just added to the design because the teardrop shape is part of the RepRap logo?

A normal hole will be ok look at metal mendel and wooden mendel for some drawings.. .

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Actually, they are in the reprap logo because they are in the part design. A reprap isn't terribly good at overhangs -- that is to say, bits of plastic with nothing underneath them, for a fair angle of "underneath". (Actually, no previously-extruded materal for them to connect with -- the direction of extrusion is far more important then the direction of gravity.) A normal hole, on it's side, would have unacceptable overhang. In order to fix that problem, reprapped parts will have a teardrop shape, so there's not too much overhang at the top.
Subtractive machining, drilling holes in wood or metal, doesn't have that problem, so just use normal holes.

if you're drilling, remember to add about 0.2mm-0.4mm of clearance - ramming M8 rod into an 8mm hole is quite tricky. imperial 11/32 or an 8.something bit would be best.

I've broken parts on my wooden mendel from trying to get M6 rod into 6mm holes, redrilling at 6.35mm (1/4") worked beautifully.

The teardrop shape is not required when building with Skeinforge either, but I think the RepRap host still needs it. With Skeinforge it can be truncated by a horizontal tangent across the top. That makes the parts stronger but does not make a nice logo!

Holes smaller than 6mm do not really need anything because the difference between a truncated teardrop and a round hole is negligible at the size with say 0.4mm layers.

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