Better to dimple or countersink?

Since I've started my wing kit, there are several places (on the rear spars) where I've run across a choice of dimpling or countersinking. So my curiousity led me to ask this question of whether a countersink or dimple makes are better (stronger, less prone to any trouble later) joint? To venture a guess, I'd say that dimples are better since you don't actually remove any material and that leaves more to support the rivet. But the more interesting question is for a 3 (or more) sheet sandwich (for example, doubler-rear spar-rib). Is a triple dimple better or is a dimple-countersink-flat joint better? My guess is dimple here again, but I'd like to know what some of you other (more experienced and/or educated) guys might think...

When faced with a choice, DIMPLE!
Mel...DAR

Zach-

For the case you mentioned, rear spar to doubler to rib, I checked with Van's and dimpling all 3 layers was the way they recommended--for the reasons you mentioned as well. I saw another builder actually countersink but, if I remember correctly, on the -9, countersinking was not an option because one of the layers (the doubler) was not thick enough for a countersink on a 1/8" rivet. There the layer you are countersinking needs to be .052 for a 1/8" countersink (if I remember section 5 of the manual correctly), yet it was something thinner I think. If possible, I always dimple. BTW--the rivets set very flush, even through 3 layers.

Steve

Dimpling will produce a better result usually. When doing multiple overlapping skins, IF the skins will support countersinking, I will countersink the bottom skin and dimple the top skin. Dimpling on top of dimpling tends to produce a small bump that can be noticeable when painted. But if the skin is too thin to countersink, then just dimple both and move on.

That's what I ended up doing. Dimpling all 3. Even though the instruction say "machine countersink", but the doubler and spar are both .040. One of those "don't take the instuctions literally" places, I guess...

I am there now, and after reading this post I think I will dimple. For once I am glad I made a mistake by forgetting to countersink yesterday... I love this site!

I do however have a related question...
Should the flanges of the spar and doublers be dimpled now, where they overlap and the skins attach? It seems like it would be easier to them dimple now rather than trying to dimple two layers of .040 at once, although I have never tried.

Thanks!

RV7Factory said:

I do however have a related question...
Should the flanges of the spar and doublers be dimpled now, where they overlap and the skins attach? It seems like it would be easier to them dimple now rather than trying to dimple two layers of .040 at once, although I have never tried.

Thanks!

Click to expand...

Yes, Brad. If you are going to dimple those parts (which I would recommend) do them first. It's pretty easy to dimple already layered joints where the material is thin (ie. spar plus rib or spar plus skin) but those doublers or the rear spar would likely distort if you try to dimple both thick pieces at the same time.

Good luck.

This article got me confused. Off course I did the countersinking as it says in the manual and noticed later on that most of you dimple. After reading all this, I started to worry about my countersinks. Definitly because of this 1/8" on .050 plate minimal remarks in vans manual section 5.

So I decided to ask Vans support about this contradiction. This is what Gus himself had to say about it:

"It's just easier to countersink these even though they are a little too thin. The plate is sandwiched with the aileron bracket later - the rivets are just to hold everything together until that is added. "

I also had one of the countersinks cut too deep with a slightly enlarged hole as result.

"I wouldn't worry about it - as above, it's all going to be surrounded by the heavy aileron bracket which reinforces the whole corner. "

Vans