Large scale - say a 777 skin lap to which I have done a few, both .190 & .250 rivets were spaced 1 inch apart - General rule was 2D min 6D max spacing with 4D as optimal. Would drill some pilot holes bout every 20th hole and cleco down, full size the thousand or so lap holes, countersink and debure. Mating surfaces were debured using a swipe of 320 paper - No material to be removed that would thin the skins. Buck tail side of holes could be debured to a max of .003 deep. Majority of external holes were countersunk according to rivet type. Sealant was applied to mating surfaces, laps clecoed down, sealant squeeze out everywhere - Yuck stuff - Load rivits, tape em down and wipe sealant off internal [sealant on a rivet acted like a lubricant causing the buck tail to be overdriven or simply explode] Had fancy buck tail gauges, general rule was 1.5D min 2D max for bucktail dia 1D min thickness - -Riveting thin stuff - Blah - Would always try to put the manufactured head against the thinest material, bucking the tail against the thickest - Thin stuff not ones favorite - Have like one shot at it - Too much force and the tail upsets the material, deforming it, not enough and the rivet work hardens - When absolutely had to buck to the thin side, often used cork over the rivet to spread the bucking force to the material itself - Thin stuff is the case where rivet length to achieve desired buck tail became one of tighter choice.
Was a skinny sh*t when I started at Boeing - I fit thru the wing tank access panels - Everything inside the tanks are sealed and god awful amount of small dia rivets . . . Quantity of Big Macs later and off to skin laps knocking down .250" rivets - Rivets like a tight hole, e.g .187 rivet to a .190 hole, larger hole and the buck tail will often club foot over - Done tens of thousands of good rivets that I don't remember, the few bad ones - - Well, when their bad, their really bad . . .
