Hole preparation prior to riveting

[Tom023]

Ok, first time builder waiting on my RV14 wing kit so I am trying to learn as much as possible beforehand. Reading the Standard Aircraft Handbook, Larry Reithmaier edition, I have come across what seem to be contradictory statements as to how many builders on this site prepare their components for assembly. I hope not to start a debate, but to get clarification of what I read in the book.

1. (p.87) "Deburring shall not be performed on predrilled holes that are to be subsequently form countersunk (dimpled)". Also, (p.94) "Do not burr holes to be form countersunk, except on titanium."

Seems pretty clear he is saying if you are going to dimple the hole, don't deburr. But, is he saying don't deburr at all, even after dimpling, or don't deburr until after you dimple, then deburr?

2. (p.112) "Avoid reaming holes for spot rivets." First, I'm not really sure what a "spot" rivet is, they neither define it nor can I find a good definition. Second, I know there have been debates about final drilling with a drill vs. reaming, is he advocating a twist drill?

Thanks for any clarification or input.

[LettersFromFlyoverCountry]

Countersinking and dimpling are not the same thing. In countersinking, you are removing metal to form a shape for a flush head rivet.

In dimpling (as we refer to it), you are changing the shape of the metal to accept a flush head rivet.

I don't know what a spot rivet is either, but I can offer this advise: Don't overthink this. Remember, a lot of those things aren't about matched-hole tooling in which the hole has already been drilled and matched.

Line up 'em up, cleco, drill to full size with the bits in your aircraft tool kit, debur, dimple, rivet.

Repeat about 10,000 times.

Fly.

[Tom023]

Thanks for the reply Bob. I understand countersinking and dimpling are different. The text in the book is referring to "Form Countersinking" which they define as dimpling. I agree it is easy to over think and that deburring seems to be a logical step, that's why I find it surprising that an authority on aluminum fabrication would state twice, that I found, not to deburr holes that are to be dimpled. The text never clarifies whether to deburr or not after dimpling, which I plan on doing, unless convincingly told otherwise.

[aerhed]

Dimpling always expands the hole. By not dimpling without deburring, you get a slightly tighter hole. The dimple dies sorta swage the hole, leaving less to deburr afterwards. There've been posts about cracks forming out of dimples that weren't deburred. I've never seen that. I have seen cracks from holes that were dimpled without final drilling first. Pretty sure that's from the pilot stretching the hole before the dimple forms. There just isn't much to deburr after dimpling. A quick swipe to chase loose chips is usually enough.

[videobobk]

One thing to keep in mind is the difference between predrilled and prepunched. As Bob said, drill them to full size. This does a couple of things, obviously makes them very slightly larger, aligns them perfectly (although they usually are anyway,) AND removes the tool marks that are perpendicular to the surface. These are the marks that can cause cracking when the material is dimpled. As the material is dimpled, it is stretched. #40 dimples aren't likely to crack, but #30 and especially larger dimples for screws are more likely to.

There has been some debate as to whether it is necessary to drill out 3/32" holes to #40 before dimpling. It is your airplane, but I think Bob said it right--cleco, drill, deburr, dimple, and rivet, in that order. Cutting corners can save time, but can lead to problems later. The old "Pay me now, or pay me later." can apply here, in matters of time as well as expense.

Bob

[Tom023]

Thanks guys, I will go with Bob's steps. Just to add a little more to the discussion, the text also states "solid-shank rivets must be size drilled before dimpling... Holes for other fasteners must be predrilled before dimpling and then drilled to size."

[LettersFromFlyoverCountry]

I think that means drill to full size before dimpling but I couldn't swear by it.

[rv7charlie]

I took a piece of scrap stiffener angle (tank stiffeners, IIRC) that already had prepunched holes, and performed all the different permutations of ways to get to a dimpled hole. From dimpling the prepunched hole to drill, debur, dimple. I also tried the debur process with a one-hole debur tool in addition to the 'industry standard' 3-flute debur tool.

I'd suggest trying it yourself, then inspect each hole under low power magnification, & report back. Also, search the archives for previously given advice on deburring, & compare the advice to what you see.

Charlie
:-}