I have read that the optimium speed for drilling small holes in thin
aluminium is something on the order of 30k rpm

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Dear Mike,

That may be true but the key is the definition of 'small' and 'thin.' (30k is
more in the realm of CNC, carbide cutters and so forth. If wer'e talking
rivets the smallest standard size is an AN2 -- 1/16" nominal diameter, in which
case the optimum drill bit rpm is about 6000, usually only obtainable with one
of those special 'needle drills.' (ie, in-line air-drill, generally used for
making the holes for data plates and the like)

AN3's need about 4000rpm, AN4's about 3000.

You can work all this out for yourself. The equation is: SFM / (.2618 x drill
diameter) = RPM.

SFM is 'Surface Feet per Minute;' a constant reflecting the type of material
being drilled. Aluminum is 100, cast iron 70, mild steel 60, alloy steel 40...
it's in all the manuals. (Or usta be :-)

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With your drill-motor running at the proper tool speed (or close to it)
aluminum is virtually transparent to the tool bit -- it takes only an instant
to drill the hole, which comes out nice and round and with square sides because
you haven't stood there pushing on the thing for five minutes, which you DO if
you're using one of those 1200 rpm drills from K-mart or, heaven forbid, that
wunnerful 560 rpm, 12v portable drill from Harbor Freight.

You'll find all this poop and more in the 'RIVETING 101' folder, in the Basic
Sheet Metal folder, in the files archive over on the Fly5kfiles Group. That's
not a real Group, by the way -- nobody swapping stories -- it's just an
overflow archive they opened up after we filled the archival space of the other
common homebuilder Groups (AirVW and Fly5k).

-R.S.Hoover