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Flat rivet lines

Everwild

Well Known Member
Just finished riveting the vertical stabilizer on my -10. And looking for pro tips for keeping rivet lines flat.

Observations are spar lines with thicker material underneath are more forgiving than ribs. The individual rib flanges seem to give more and allow the skin to more easily deform.

I understand it's important to balance the pressure between the gun side and the bucking bar. The right air pressure is important. Any other pro tips out there for getting smooth rivet lines?

I used a 2x gun with a 1" mushroom set from Cleveland. Thanks!
 

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Dimpling

Sorry for the criticism, but what I see are "under dimpled" holes. It creates that optical distortion. Riveting technique won't fix it. Fix the dimpling issue and the skin will be optically flat. The riveting looks ok. They don't look like mushroom set deformations.
I prefer a swivel set. It's a little more forgiving of alignment.
 
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Sorry for the criticism, but what I see are "under dimpled" holes. It creates that optical distortion. Riveting technique won't fix it. Fix the dimpling issue and the skin will be optically flat. The riveting looks ok. They don't look like mushroom set deformations.
I prefer a swivel set. It's a little more forgiving of alignment.

I agree the holes are under dimpled. I exclusively use a non-swiveling mushroom set with a rubber ring around it, except when there is a tight spot, I find the swiveling kind to work great in those locations.
 
No criticism taken! Looking to get better and appreciate the feedback.

But I am a little confused, because all of the dimples were done exactly the same way, with a DRDT2. I'm getting good witness marks on both sides of my skins with the dimple dies.

The rivets in these photos where dimpled exactly the same way and look crisp to me. All of the rivets that where squeezed along the edges look great also. So I'm not totally convinced that it is an under dimpled issue?

My gut tells me I beat up the manufactured head side with the rivet gun and need to try lowering the air pressure and put a little more pressure on the bucking bar once I get an initial set. I'm all for buying tools. Anyone have a C-frame they want to sell me?
 

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Two things happening

I see a couple frustrations:

I agree that the dimples were probably not crisp to start with. Dig into that subject for all manner of opinion on method and die shape.

There also is something going on where the mid rib is meeting the aft spar. This kind of thing bit me early on in my build. There are a lot of ways that a perfectly shaped substructure or perfectly bent skin might get to less than perfect by the time you start building. I put way too much faith in the idea that if I did the assembly without mangling the parts, then I would get a nice flat assembly. Didn't always happen. BTW, Nothing wrong with a little optical distortion here or there, especially if you intend to paint.

But if you want as flat as you can get then you have to really look carefully at the cleco stage. Is there any preload in the skin when you mate it to the substructure? Are the substructure flanges at the right angle? (correct angle and not 'right' angle; not all are meant to be 90 deg) Are the substructure flanges where they need to be? Is a shim or a flange tweak called for?

Once you get to the wing ribs you'll be more comfortable adjusting these things. But if you can start earlier?
 
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Once you get to the wing ribs you'll be more comfortable adjusting these things. But if you can start earlier?

Awesome insight. A new level of variables to think about.

Yes, I have basically been trying not to muck up the parts during processing, deburring etc for assembly. Outside of fluting, I haven't messed with the geometry of flanges etc unless otherwise instructed. Will look more carefully as I move on to the horizontal stabilizer.

I'm generally happy with the outcome. The mirror finish and all of the stuff in my shop makes the distortion look much worse in the photos than it is. I do plan on painting, but would prefer to improve my technique as early as possible and not rely on cover-up to hide a bunch of goofs.

Do the dimples in the second batch of images also look under dimpled to you? If so, I'll try a C-frame. This is as much of a squeeze as I can get on the DRDT2 using the standard Cleveland dimple dies.
 
But I am a little confused, because all of the dimples were done exactly the same way, with a DRDT2. I'm getting good witness marks on both sides of my skins with the dimple dies.
...
Anyone have a C-frame they want to sell me?

Don't switch to the C-frame. All my dimples are done with the DRDT-2, unless I physically can't reach them with that tool.

It is important to make sure the DRDT-2 is aligned properly, and also that you applying sufficient camming force to the dies with the lever. It should take some real effort to bring the lever over center.

I agree some of those dimples look good, but the ones you photographed from an oblique angle definitely look under-dimpled to me.

Once you get the DRDT-2 set up well, it will work beautifully and consistently every time. It doesn't take too much effort, but it needs to be done.
 
Skin creep

I don't know if your instructions covered it but there is another possible contributor here.

There is a can of worms debate around whether using the same dimple die on top and bottom layers is the best way to go. Rather than opening that can of worms let's just accept that if we use the same dies on top and bottom then there is going to be some adjusting when we compress those rivets.

If we start on one side of a rivet line and work toward the other we can potentially create a wave of slightly stretched skin.

So if your instructions haven't covered it already try to get your skin tacked down in several places before you fill in the rest of the rivets.
 
This handle mod may help

Hi David. The DRDT2 makes excellent dimples. Crisp sides and flat lines. U need to get your pressure (cramming force, per 1001001 above) adjusted.
To make it easier, i modified my handle per the pix below. This may help u. It adds leverage and also allows u to dimple the large skins without the handle hitting the skins on the final downstroke.

I used 1/4” steel and made a “V” shape and attached it to the top of the actuator and moved the handle to the other leg of the “V”.

This contributed to my Outanding Workmanship award at 2019 Sun-N-Fun.

Good luck.
 

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Riveting sequence

Another thing to check is riveting sequence, which is to work from centre out along a line and down to up along a row of ribs. We don't generally tack down the ends and then fill in between as if we were sheeting a building with plywood.
This sequencing will be important on the wings and fuselage to help prevent oil canning.
 
Over fluting?

Is it also possible that I over fluted those ribs?

Everything else looks really good except the middle horizontal row of ribs. Could I have shortened the distance between the holes with the fluting tool just enough that it caused the skins to pucker just a little??
 

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Is it also possible that I over fluted those ribs?

Everything else looks really good except the middle horizontal row of ribs. Could I have shortened the distance between the holes with the fluting tool just enough that it caused the skins to pucker just a little??

So long as you aren't overworking the flanges by going one way then the other, normal overfluting would induce a bend the other direction. Flute until you get it straight even if retains a slight twist.

Did you flute then drill, or drill then flute? Not sure if the latter is even possible with our pre-drilled parts but would definitely give you grief. Something you would probably have noticed on re-assembly.
 
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also

You might also try a 3x gun; it takes less strikes and the gun has more mass. Two short "blips" on the trigger sets the rivets nicely.
 
Under dimpled

The second photo where the row crosses your white T-shirt from top to bottom also show some optical distortion. Why? I still think they are under dimpled but it could also be an issue with the DRDT platform. I ruined a top aft skin long ago. The platform wasn't perfectly aligned with the mating of the two dies. The result looked a little like that except the all puckered out. Something to check.
I am a believer in Occam's Razor. The simplest solution is usually the best one.
Start simple. Thankfully that skin has been used for all sorts of other parts so it wasn't wasted. I learned a lesson too.
I also love C-frame dimples but that's another can of worms.:D
 
Hmmm , couple of questions to start… Are you using the spring back dies from Cleveland? What pressure are you running on the gun? What bucking bar are you using?

If you are using the spring backs, add another 1/2- 3/4 turn on the drdt and dimple. The equal pressure on gun and bucking bar didn’t work for me so try… Make sure what you are bucking is well secured, push pretty hard down on the machine head with the gun and just barely touch the tail of the rivet with the bucking bar, slowly press “tease” the trigger while slowly adding pressure to the tail of the rivet with the bucking bar and more squeeze on the trigger, until the rivet is at the smush you want. Play around with it, find what works with varying pressures, pretend it’s a dance with the you, the gun, the bar and the rivet.Also try putting a small piece of blue tape over the head of the river while bucking.
 
HS rib flanges

Related to this thread, is this an example of needing to bend the flanges of the ribs to 90 degrees so they are parallel to the skin and spars? Assuming that might help some with the wrinkles?

I didn't adjust the rib flanges on the VS as it seemed like they aligned pretty well with the trapezoidal shape.
 

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I'm not a -10 guy

Specifically, I don't know if the middle of that rib has a rise in it.

But the end should have a flange that matches the spar both in flange angle to spar line, and the skin should just lay on the spar and the rib at the mating area without one or the other pushing the skin outward.
 
I'm not a -10 guy

Specifically, I don't know if the middle of that rib has a rise in it.

But the end should have a flange that matches the spar both in flange angle to spar line, and the skin should just lay on the spar and the rib at the mating area without one or the other pushing the skin outward.

Thanks! Yes, that rib has a little bit of rise in the middle and the camera angle makes it look high at the spar end, but the right side lines up well with the spar. So everything needs to be co-planar as much as possible. I did not really chck that on the VS.

Time to build one of those flange bending tools.
 
Wooden flange bender

Thanks! Yes, that rib has a little bit of rise in the middle and the camera angle makes it look high at the spar end, but the right side lines up well with the spar. So everything needs to be co-planar as much as possible. I did not really chck that on the VS.

Time to build one of those flange bending tools.

I built mine for the wings, but should have done so right from the start. I built mine with a slight curve at the 'shoe' that makes you take smaller bites but allows you to adjust around corners. Use some oak or something hard for the form and lever.
 
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