We could potentially up-size the hole by a mm or two (has been drilled out since that picture) but we're reluctant having experienced the power involved.

Well, Mario has extremely kindly offered to help. We think making it to the House of Chaos shouldn't be too difficult, in which case we'll have at least one skilled person leaning over the thing who will guide us. If he thinks a bigger hole is necessary, may a bigger hole be drilled!

I have a feeling he intends to just weld the buggery out of it, though. :P

We'll build this, avoid breaking it, be happy, and let Mario do the thinking if we can stop by.