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I've got a glass box that measures 900mm x 450mm x 450mm.

The width of the glass is about 6mm thick.

If I drill, cut, or grind a small hole in/through one of the faces; will it significantly affect the structural integrity of that piece of glass?

I'm concerned it might become prone to flexing, and cracking; if I pick it up to move (or transport) it, for instance.

Is there some kind of ratio, or formula that I can use to determine a relatively safe size, and adjacent edge distance for an aperture?

If you're wondering: It's basically a small indoor display garden / vivarium type situation, which needs at least a single outlet point through which gravity can be allowed to drain the excess fluids from the soil.

glass box schematic diagram

voices
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3 Answers3

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While I cannot cite any specific sources for this, I'm going to posit the following answer:

Yes, structural integrity will be affected, but not enough to be concerned about.

The box you describe is not suitable for carrying any kind of load anyway, and as you state above it's for display purposes. Drilling a tiny hole will not cause any cracking - in fact it's a technique used in windshields (particularly aviation windshields used in small planes) to STOP cracks from continuing to spread. (Small hole drilled right at the leading edge of an expanding crack relieves the stresses in a sound manner)

Granted aviation glass is different than what you've got but still - I think you're fine. I'm curious though why drill a hole in it? That will have a tendency to trap moisture.

The Evil Greebo
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Once you successfully (!) get the hole drilled, there's little concern. Not cracking it while you drill it is the hard part.

I'd say ~2 inches in from a corner, or at least an inch on a leading edge. The thickness of the glass will ultimately determine how close you can get - and remain successful.

IIRC, the general rule for the bare minimum distance from an edge, to drill a hole in a structural member, is four times its thickness.

(anecdotal supposition)

I've heard that all panes of glass have a sweet spot. I'd assume it lines up with one of the 1/8th harmonic intervals. So on a 24" pane of glass, trying to drill exactly 3" or 6" in could be trouble. But it probably has more to do with how it's mounted, which means for drilling it, it should probably be on some hard plastic, not e.g., on a towel on a table.

Mazura
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There are a great number of aquariums , many with similar dimensions with 1 or 2 holes in the bottom, typically 1.5 inch diameter , with no structural problems. And they carry more weight than your terrarium . Actually , you could just get an aquarium , you wouldn't even need a drawing of it.

blacksmith37
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