J

JBSmitty

I'm New Here
Hello all,

I am working on the Horizontal Stabilizer on a RV-8, and have a very basic question.

The instructions say to dimple the spars using a pneumatic or hand squeezer and the skins with a C-Frame, which I have done. (My micrometer tells me that they are both .0325")

Prior to riveting, I thought I would double check my work and cleco a spar to the skin, and what I see is that the dimples seem to sit flush in each other, but now I can see in certain locations where the skin does not sit perfectly flat on the spar in between the dimpled holes. Is this okay? Rivets sit flush in all the dimples (both skin and spar) but I am concerned that I have not dimpled correctly.

Thanks in advance.
 
NOT AN EXPERT

JBS,
I am in no way an expert and not completely sure I am understanding your question, but if you are saying the rivet would be lose if you pressed down on the skin so the skin was tight to the rib, that doesn't sound right. I believe the last thing you want is the rivet to be able to move around. I think they call that a "smoking" rivet because it rubs on the skin and makes a black mark around the rivet.

I found that when I was bucking the rivets, if I wasn't careful and put the pressure on the rivet guu, pressing the rivet to skin or rib, and just let the bucking bar use its own weight to smash the back side of the rivet, I got the rivets tight.

Maybe a picture - if you can figure out how to post one! would help. Good luck. Im sure others here will help get you on track. Good luck with your build.
 
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JBSmitty said:
Hello all,

I am working on the Horizontal Stabilizer on a RV-8, and have a very basic question.

The instructions say to dimple the spars using a pneumatic or hand squeezer and the skins with a C-Frame, which I have done. (My micrometer tells me that they are both .0325")

Prior to riveting, I thought I would double check my work and cleco a spar to the skin, and what I see is that the dimples seem to sit flush in each other, but now I can see in certain locations where the skin does not sit perfectly flat on the spar in between the dimpled holes. Is this okay? Rivets sit flush in all the dimples (both skin and spar) but I am concerned that I have not dimpled correctly.

Thanks in advance.
Click to expand...

Here is a common problem that I've seen with new builders. Often, when squeezing dimples with a pneumatic or hand squeezer, the dimple is not properly formed. This can also be a problem with a c-frame, but is less likely.

The root cause of this with a pneumatic squeezer is twofold. Firstly, the squeezer dies must be adjusted just right. The two should be in contact with the squeezer actuated, and you should just be able to rotate one of the dies with your fingers.

The second problem is that the squeezer yoke may be bending. This is more of a problem with a longeron yoke than the other yokes, or with cheap yokes. A bending yoke means that the dimple will not be properly formed. Adjusting the dies so they are more together helps this.

Ultimately, after you squeeze a dimple, it must be perfectly formed with no deforming of the skin around the dimple (waviness when held to the light) If you have any deformation of the skin, then dimples will not nest together very well.

If the dimples in the two parts are well formed, then you have nothing to worry about.

The C-frame produces better dimples, but only if you hit them with the right force. Again, check to make sure that the dimples are well formed and the skin around them has no waviness.

In conclusion, when I've had problems with a squeezer forming a good dimple, I use the C-frame. Give it a try.
 
Thanks for all the replies and the welcome to VAF.

I do have a DRDT-2 which I used for the skins, and the spars where it would fit. Looking closer, this is only really occuring where I could not get the DRDT-2 to work on the spars. I used a pneumatic squeezer here, followed up by a hand squeezer. Dies were set as described above.

Everything fits pretty well, but where I did not use the DRDT-2 on the spars I can see where the dimples do not fit as nicely. Maybe time to go to the gym and strengthen my hands! I'll take another go at the hand squeezer on these, as my pneumatic doesn't have the juice to do more.

As a separate issue, the nose ribs on the horizontal stab are a real pain to dimple. I used pop rivet dimple dies, but these dimples are no where near as nice as with the DRDT-2. I discovered if I put a bend into the horizontal stab skin similiar to what it will be assembled, I got a much better dimple, but they are still inferior to the other dimples. Is there a better solution?

Thanks again for the replies.
 
Dimpling

For hard to reach spots I use a countersunk monel rivet, hammer, punch into a countersink cut into a piece of steel. I'll toss the rivet after two or three holes. As for the original question, I think you are asking if its O.K. that the skin doesn't sit flat when the dimples are completely nested together.I recall a reference from a Convair 580 SRM that listed acceptable gaps between skins and or structure after riveting, .008" or something. They also had a chart showing strength of various fastener types, and nested dimpled joint were by far the strongest. Usually what happens is the last bit of forming takes place when the rivet is set, eliminating small mismatches and making everything sit alot tighter. Try it out on some scrap.
 
Tip

Another trick I learned is to use a little rubber grommet when squeezing rivets. (Harbor freight sells a bunch for cheap) I put it over the shop head side of the rivet before I squeeze it, as the squeezing begins, the rubber squeezes the two metal pieces together just before the shop heads begin to form. It works great and I wish I would have learned this trick earlier in the build. I have also noticed that the shop heads are a little under driven so I go back and squeeze again without the grommet.

Hope this help out.
 
I've found that using tank dies on the structure and standard dies on the skin gives me more consistent dimple nesting.
 
longranger said:
I've found that using tank dies on the structure and standard dies on the skin gives me more consistent dimple nesting.
Click to expand...

+1 on the tank dimple die.

I'm also going to add a little bit of wisdom I learned from Van's tech support about nesting your dimples and countersinks.

You can't judge how well your parts will fit together by how they look when they are clecoed. The rivet exerts far more pressure and will pull the parts together very well even if there were gaps when you clecoed them together.

I learned this when I countersunk some holes in thinner stock. I thought I had to countersink the part enough so that a dimpled part would set into it perfectly.

The only problem with that is - if you do that in thin stock the hole becomes too large for a 1/8" rivet. When I called to ask if I should use the "oops" rivets in these parts, first they said yes I could, but then the nice fellow at Van's added not to countersink the parts so much, just do it to the point you start to enlarge the hole (or right before if you can judge that well) and the rivet will pull the pieces together nicely. The dimple will actually flatten into the countersink under pressure from the rivet.

I now put a few rivets in, then check for gaps before continuing. If there are none I know I am good.
 
Having just dimpled my HS I understand what you mean. Today was my first time with the pneumatic squeezer. I did all the dimples in the skin with the DRDT-2 as was needed. Then I switched over to the p-squeezer. What I found is that the DRDT-2 dimples were much more consistent and my squeezer dimples seems a bit shy of where they should be. I adjusted the air pressure and that didn't seem to help much. I then adjusted the dies as Vern has suggested above. PERFECT consistent dimples. I DID, however, have to periodically tighten the adjustment of the dies as they would get loose after 15 or so dimples.

Haven't checked the fitment of ribs/skins yet but I hope they are sufficient enough to let the rivet do any remaining work.
 
tkatc said:
... I then adjusted the dies as Vern has suggested above. PERFECT consistent dimples. I DID, however, have to periodically tighten the adjustment of the dies as they would get loose after 15 or so dimples. ...
Click to expand...

I've had the same issue. I put a fat sharpie mark on the adjustable set and one on the squeezer frame so I can make adjustments before it gets too loose.
 
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