Jeff Neville,
Re your post of 2/3/2104 @ 5:00 PM
When I've drilled out say a 1/8 inch rivet from an existing structure I am directed to re drill the empty hole with a somewhat larger drill i.e. drill out w/#40 drill and redrill w/#42 and then put in an "oversized" 1/8 rivet.
Has this practice changed over the years?
The practice I've always known and followed was to use care in drilling only deeply enough to 'pop' the head of the rivet off, then 'punch' the shank and remaining tail ('buck' tail) out of the hole, leaving hopefully a nearly pristine hole at its original size.
This works well much of the time when the mechanic is experienced and the original hole is good. I've probably drilled a million heads off without touching the base metal - drill down through the 'dimple' nice and straight (you learn to compensate for bit drift quickly and keep it centered when drilling lots of these), then 'pop' the head off with a flick of the bit at the end by 'leaning' the drill slightly; if you drill true, this works like clock work. Then come behind with an awl and hammer and rap the tails (shank and tail) out of the hole with a sharp blow (not like driving a spike - just a light but sharp rap).
That said, sheetmetal, like the world, isn't perfect - so frequently one cannot readily punch the shank out and must drill part way - or sometimes all the way, through the sheets to remove it. That happens typically where the original hole was somewhat large and irregular to start with. When that happens, one often is stuck going to the 'next size' - which in the case of the 3/32" rivet ("#3") would mean a 1/8" rivet ("#4"), not two sizes up (5/32" or "#5"). Driven rivets are nice in that they can cover a multitude of mild sins in terms of slightly egged and tapered holes - but that should not be over-done or you lose strength. A perfect hole is desired, of course and it is better to 'true' the hole next size up.
Would this account for the differance in a #3 rivet nominal dia. and the hole size in 2-2-V-1 of 5/32in.?
Ted Campbell
I would expect a 5/32" rivet to be a typical replacement for a #4. To see an entire row of #5 rivets suggests they are original - not surprising to see where a keel beam or stringer is concerned, but I don't know the L10 structure that intimately. At the very least I would have thought of the keel-skin rivets being at least 1/8" (#4), not #3 - but what do I know about what Lockheed was doing in 1937 without drawings in-hand. I would have thought it more likely to find original #5 rivets there, actually - which would be consistent with the guidance I quoted up-string here (and linked to AC 65-15).
The rivets I can see on the sides of the bird in lots of photographs (some very clear) appear to my mechanic's eye to be typically #4 by and large, with some larger #5's in areas of concentrated stress, e.g. heavy stringers, gusseted bulkhead intersections, etc. That is more typical. That the belly would have smaller rivets is odd to me because it is an area that is in tension for not only flight, but ground ops - that belly keel absorbs a fair bit of tension (with the skins) as fuselage bending moments occur during taxi, loading, etc. Meaning only that I'm surprised that the belly would have smaller rivets - but again, what do I know about Lockheed's practices of the day, and I'm going by my eyeball estimate of what I see in the photos and am not laying hands on to see up close.
In any case, this artifact is all the more peculiar to me in that it has these light rivet holes - but if that is what Lockheed did on the original structure, then no surprise I guess. I wish we had the drawings of that area.