Machine c'sink in thin material

I have finally started my -12 kit and ran into my first problem already.

On page 06-04, step 2 where it says to machine c'sink the six #40 holes. This seems to be counter to what Van's says on page 05-05E where they say "While it is acceptable practice to machine c'sink metal as thin as 0.032" for an AD426AD3 (3/32) rivet, We recommend dimpling in metal 0.04 and thinner".

I went ahead and did the machine c'sink as directed. However, since I had de-burred the holes on the other side maybe .005" deep, now the hole is about .012" oversize.

In examining the location of these rivets which are only 6 of many rivets and bolts holding the spar caps inplace, it would seem to me that the slightly oversize holes would be a very minor issue and I should just proceed. However I don't want to start making assumptions about quality compromises without some input from others with more experience and knowledge than me. Any advice would be appreciated.

Wayne

WayneJ said:

.......I went ahead and did the machine c'sink as directed. However, since I had de-burred the holes on the other side maybe .005" deep, now the hole is about .012" oversize. .........

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Wayne,

I suggest you do some practice on scrap material. Drill some #40 holes and practice deburring and sountersinking. It sound to me as if you deburred too agressively. You should only take off the rough edge, not sink the deburring tool into the metal. Perhaps you also set the countersink tool to go too deep. Start shallow and increase gradually, until a rivet inserted comes just flush, no deeper.

If you think those 6 holes have gotten way too big, you could probably step up to -4 rivets - but you should check with Van's first before making that change.

John

Help is close

Wayne,

Hal (N912HM) and I will both be at my hangar in Auburn Monday morning at 10:00 a.m. getting my wings back on. Bring the part by and you will have 2 experienced RV-12 builders to knock heads with.

Tony

WayneJ said:

......I went ahead and did the machine c'sink as directed. However, since I had de-burred the holes on the other side maybe .005" deep, now the hole is about .012" oversize.

Wayne

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One of the major suppliers, Spruce I think, sells something called rivet savers. These are countersunk rivets whose shaft is one size larger but the head is the original size. Once the rivets are squeezed, they all appear the same from the flush side. The kit is $15 or $20 and includes a variety of sizes. I bought the kit and never used any of them (yet). If you'll PM me your postal address and the exact sizes you need, I'll mail you the ones you need.

Jerre