Hmmm! Still got reservations!
I agree, firstly you’ve got to have the nous* and the equipment, to even contemplate going down this route. Let’s face it, there are people that are adequate mechanics, there are a lot more who have five thick stubby thumbs on each hand and then there are the few that have that special “feel” for the game. It seems pretty clear that Douglas Kephart falls into the latter category, his was a clever bit of lateral thinking that worked.
But if you are not totally confident in your abilities and equipment just don’t go there!
The points about the possibility of the oxide layer forming a thermal barrier and the conduction path is fair enough but my reservation here is that the conditions inside the holes cannot be known with any certainty and thus cannot be relied upon.
By the way, given that the job succeeded with about 250A I don’t think my first order guesstimate of 300 amps was too bad!
Douglas says there is no risk of locally melting the aluminium, well fair enough, maybe not in his hands but there would be a lot of heat going in and I still see risks. The comment about damage by arc burning and his stricture about really good earthing is to be taken seriously.
Another point, some of the castings I’ve got are a bit flaky, a lot were made at a time when the metallurgy was in its infancy and seem rather soft with a bit of porosity. Also I’ve heard that the factory was almost always impoverished and you can bet the bean counters had an eye to cost over the best alloy for the job, not the best starting point and these castings are not getting any younger either!
I’ve pointed it out before, aluminium is an extremely reactive metal, (Space Shuttle booster rocket fuel and thermite welding of railway track come to mind); the only reason that it doesn’t normally burn like magnesium and stays nice ‘n shiny is the almost instant thin impervious oxide skin that forms. There are other factors too, so all in all and notwithstanding Douglas’ success; I just don’t see the need to take the risk when there is an alternative.
Anyway, after brutalising the studs in this way I’d not want to use them again for anything other than a pattern so they are still my candiate for sacrifice.
Oh! Yuss! For them wot don’t know their proper English ‘ow she is spoke:-
*Nous /nowss/ n. Brit. colloq. Intelligent perception; common sense; gumption. He! He!
