Dimpling "Paranoia"???

txaviator · #1 04-23-2005, 07:50 PM

As I stare at my recently completed horizontal stab, I wondered something....

As I look down the lines of the rivets, there are slight indentations around every rivet. In other words, all rivet locations have a slight indentation about 3/4" to 1" in diameter. I got to thinking about the entire process, and a dimple die is a dimple die...I didn't knock the **** out of the C-Frame while dimpling, and I think what I see is normal?

I suppose what I am asking, is if a slight indent is normal as we use the dimpling theory on these RV's? I have never thought about checking it out before, on the existing RV's that I have seen which were still 'naked'. And recently, all the RV's I have seen were painted.

Can anyone offer any input? I looked through tons of photos online, and can't really notice any indents in other planes?

Thanks!

szicree · #2 04-23-2005, 08:45 PM

I think in most cases a very slight indentation is to be expected. We are talking about after setting the rivets, right? I'm not sure what type of rivet set you are using, but I found that I could get much better results with the big swivel type like Avery sells.

txaviator · #3 04-23-2005, 08:46 PM

Yes, after setting all the rivets. And that is exactly the rivet gun head I used: the large, rubber-headed version from Avery's.

n2prise · #4 04-23-2005, 08:51 PM

The only photo I have that has close-up photos of dimples is on my page 7 as I started the wings. http://www.n2prise.org/rv9a007.htm Look down at the next to last photo and you will see that only ONE dimple to the right of the landing light template has any mark at all. I dimpled all the holes before I removed the blue plastic. That may have made a difference.

The most skin damage I received came from riveting. But don't worry about that too much, since the entire surface of the airplane gets sanded before painting. Now if you are planning a polished, bare aluminum airplane, that would be different.

Jerry K. Thorne
RV-9A N2PZ
(ready to move to the airport)

Captain_John · #5 04-23-2005, 08:58 PM

Well, ummmmmmmm...

Something that no one else had mentioned... and caught my attention was the fact that you said the indentations were 3/4" to 1" in diameter. I am suspecting the indentations are actually dents caused by the flush set you are riveting with.

I too had this problem when I started my HS. It seems that I was using too much pressure on the rivet gun.

How many PSI are you using?

CJ

n2prise · #6 04-23-2005, 09:05 PM

CJ is correct. I use a regulator in front of the 2X gun with 25 to 30 PSI when doing the small rivets. The #4 rivets get 40 to 60 PSI depending on where they are. Riveting through the longerons on the fuselage takes more pressure than doing rivets on skins and ribs. Use the squeezer for as many rivets as possible to minimize the skin damage.

Jerry K. Thorne
RV-9A N2PZ

Captain_John · #7 04-23-2005, 09:14 PM

I watch CSI.

CJ

Bob Axsom · #8 04-23-2005, 09:49 PM

There is a certain feel that you should shoot for regardless of the PSI's. If you have the small gaugeless regulator screwed into the input of your gun you can place the rivet set against your work bench pull the trigger and feel the hammer pressure (as BRRAAAAAAT) adjust the dial a click or two if it doesn't feel right and repeat. Then drive your -3 or -4 rivet in some scrap aluminum and check the results. There should be no eyebrows or other deformation marks on the skin and the rivet should meet the installation requirements. If you damage the scrap or the rivet installation is not acceptable dial in or dial out a click of pressure and repeat the process until the results are acceptable. THEN go to the real airplane work. After a while you just pick up you gun, insert the rivet set, do the bench hammer test, adjust for the right feel and go to work. It gets about as natural as walking. If your concern is some very superficial marking with no deformation of the skin it means nothing. If you have a ding then you have to fill it and forget about the polished aluminum skin or replace the skin and try again - once they're in they are not going to come out.

TShort · #9 04-23-2005, 11:58 PM

Something else to consider ... I had a similar thing on my -8 empennage which has somewhat thick (.032) skins; the only dimpling I had done was on the "project" which is thinner.
I found that not dimpling hard enough left a depression around the dimple; i.e., if enough force to actually force the dimple dies together was not used, then the skin around the dimple was deformed. Amazingly, this was corrected by going back and hitting the dimples again with a much firmer smack.
You can sort of see it here (esp. where the light reflects...):

I don't have an "after" picture available now, but after a second much firmer hit with the hammer they look the way they should.

Thomas
-8 empennage
wings kit ordered...

f1rocket · #10 04-24-2005, 08:26 AM

Another trick to getting the rivet heads to set is to run your deburring tool in the dimple about two to three turns. It cuts down the rounded ridge at the top edge of the dimple transition with the skin and allows the set rivet to seat just a hair deeper. The trick is to not remove a bunch, that will weaken the joint. All you need is two or three light turns.