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Skin scratches and imperfections..

Palamedes

Palamedes

Well Known Member
Hey folks,

So I'm working on the elevators on my -10 and noticed that one of the skins is fairly scratched up just due to man handling on my part, placing it on surfaces it shouldn't have been.. back rivet plate with rough edges..etc.. all the things.

I hate it. I looked over all the skins that I took the vinyl off of (wont do that for the wings) prior to working and took a picture of the worst one:

IMG_1287s.jpg


How bad is this? I have tried to be careful but it seems nothing will stop some amount of scratching and marking of the skin.

I need to get a really short/soft carpet to cover my work bench obviously, but too late for this piece.

Is this something I shouldn't worry about because it will disappear with paint or should I do something about it now? etc..

Looking for suggestions here.
 
I believe generally the rule of thumb is if that you can run your fingernail over the scratch without it catching, it's okay, if not, should be smoothed out at least. Your painter will scratch it before painting anyways, so I wouldn't worry too much as long as they aren't deep.
Chris
 
Last edited by a moderator:
From what I've read, if you're planning to paint, they will do far worse to your skins to scuff for the primer!

If you're going to polish, you might want to reconsider your approach.

I have a piece of carpet that I lay over my bench when I'm not drilling or deburring. I'm also keeping the vinyl on until after I have the piece completed. I pull the vinyl off of the rivet lines before drilling, deburring, dimpling, riveting.
 
I'm absolutely planning to paint and these scratches are really visual only.. you can't even feel them..

Okay that takes a load off my mind.. thanks.
 
Now that that is resolved I will offer an unsolicited suggestion/tip.....

I can tell from your photos that your dimpling technique is not quite as good as it could be.

What process are you using to dimple out in the middle of skins?
 
One thing that really helps me with scratch resistance is my method of priming parts. For me, it really speeds things up, and helps protect parts during the build.

After I complete smoothing all the edges and de-burring the holes and cutouts, I then go over with a mild scotch bright pad (unless an exterior skin that I may want to polish aluminum later). I then clean off the part with a clean rag damp with a good de-greaser and let dry.

Then I use a sponge brush to brush on a thin metal etch primer (I use dupont veri-prime) I mix it thin and can make a thimblefull if a small priming job.

I sponge on prime before I do any dimpling, as the dimples will squeeze extra primer out of the brush and can cause drips on the back side.

No spray no mess no fuss, and it goes quick. And IMHO provides a durable barrier to corrosion, and also seems to make them scratch resistant.

oh4i74.jpg
 
Also added an image on my dimpling set up which seems to work well. Basically, I have buried a bucking block with male dimple die in my work bench, then slide my skin over to set the hole on top of the male dimple. Then a quick shot from my light gun with a swivel female set. Some people use laser pointer so you don't 'loose' the buried male dimple die. But i seem to be able to find it without pointer.
50nt4k.jpg

2aajchw.jpg
 
rvbuilder2002 said:
Now that that is resolved I will offer an unsolicited suggestion/tip.....

I can tell from your photos that your dimpling technique is not quite as good as it could be.

What process are you using to dimple out in the middle of skins?
Click to expand...

I use a DRDT2 dimpler.

Now you have me worried! What is wrong with it? Note; it might be the image..

Here is another close up of dimpled vs non-dimpled on the elevator.
IMG_1265s.jpg


The rivet's sit down in there perfectly. Its 100% smooth when you run your hand over the final product..
 
ERushing said:
From what I've read, if you're planning to paint, they will do far worse to your skins to scuff for the primer!
Click to expand...

+1

I have painted most of my plane already and it was hit with 80 grit on a DA (equivilant of 150-160 grit) before primer. Cosemetically speaking, the scratches will all be covered up. You only need ot worry about the deep ones that can cause structural issues.

Larry
 
Palamedes said:
I use a DRDT2 dimpler.
Now you have me worried! What is wrong with it?
Click to expand...



No need to be worried....
It is fully acceptable from an airworthiness standpoint, just not to the finish quality that it could be. If you are happy with it, that is the main thing.

But, if you desire to learn, the easiest way for you to see what I am talking about would be to take an already dimpled skin to the shop of someone that owns a C-frame tool and then re-dimple a few holes. Then view the reflection in the skin around the dimples. A crisply formed dimple will have no distortion of the reflection right up to the very edge of the dimple. Each of your holes has a distortion that is about 3/4" diam at each dimple. This is a classic indicator of dimples not being formed quite fully.
 
After what I have read I am not sure how much sanding should be done to prep for paint. The thing is that any abrasive that takes off metal is reducing the thickness of the skin and rivet heads. This produces an unknown strength. My test for any scratches is a scotch brite pad (the red ones). while I know that this is an abrasive it is a very fine one. If the scotch brite gets rid of the scratch I am ok with it. Every one has their own standards, that is why it is "Experimental".
 
rvbuilder2002 said:
No need to be worried....
It is fully acceptable from an airworthiness standpoint, just not to the finish quality that it could be. If you are happy with it, that is the main thing.

But, if you desire to learn, the easiest way for you to see what I am talking about would be to take an already dimpled skin to the shop of someone that owns a C-frame tool and then re-dimple a few holes. Then view the reflection in the skin around the dimples. A crisply formed dimple will have no distortion of the reflection right up to the very edge of the dimple. Each of your holes has a distortion that is about 3/4" diam at each dimple. This is a classic indicator of dimples not being formed quite fully.
Click to expand...

hrmm they seem fully formed.. I mean the rivet sits down in them perfectly. Could it be a factor of the rivet gun? maybe I have too much pressure or am pushing too hard?
 
Palamedes said:
hrmm they seem fully formed.. I mean the rivet sits down in them perfectly. Could it be a factor of the rivet gun? maybe I have too much pressure or am pushing too hard?
Click to expand...

"Fully formed" means deep enough for the rivet head, AND having a well formed dimple. The metal should be flat right up to the edge of the dimple, with no distortion around the edges. If you don't get enough "squeeze" (or "smack") on the dimple dies, you'll get a dimple that's deep enough for the rivet head but doesn't have the well defined shoulder around the edge. I have found that one benchmark is that if you've got enough squeeze, you'll have a ring around the dimple on the outside where the die marks the skin just enough to see it.

I was dimpling today with my pneumatic squeezer. After doing half a dozen of them I looked at the outside of the skin -- no rings, and you could definitely see some waviness around the edges. I needed to shim the die a little more. A -10L washer did the trick.
 
Palamedes said:
hrmm they seem fully formed.. I mean the rivet sits down in them perfectly. Could it be a factor of the rivet gun? maybe I have too much pressure or am pushing too hard?
Click to expand...

I can tell from your photo of the un-riveted skin, that they are not. Another way I can tell is in your photo of the riveted assembly, even the rivets that would have been back riveted are also not flat around the dimples.

It is not a factor of the rivet not laying down fully in the dimple, it is that the skin is no longer flat adjacent to the dimple, after you have done the dimpling process. If it is done properly, the skin overall will be perfectly flat (reflection will be distortion free) after dimpling except for just the diam. of the dimple.

As I said before, if you are interested in learning the difference, use a different tool to redimple some holes and compare. If the C-frame is used properly when you re-dimple, I guarantee you will be able to see a difference. I say if because people under form dimples with a C-frame tool all the time also. It is nothing specific to your tool, though I seem to see it more often with builders using the DRDT2.
 
Jason,

If it's hard to see what others are describing as under-dimpled, try laying a straightedge, on edge, along and on top of the rivet line. If the dimples are fully formed, there will be little to no light between the straightedge and the dimple/rivet area. In other words, the skin will be perfectly flat, even around the rivets.

Just another way to look at it...

Charlie
 
Thanks everyone! I very much appreciate your input and will research/try to do better.

How will the current under dimpling affect the final aircraft? is it doomed at this point or is this just cosmetic?
 
Purely cosmetic. Save the worry for when you make a real mistake - and then just remind yourself that there's nothing that time, money, or both, can't fix! Not that having an eye for detail isn't important, and it's good that you are starting out with high standards. Everybody learns on their empennage, and many often rebuild part of it, me included. But I wouldn't worry about those skins. The imperfections will probably be less visible when painted, anyways.

Chris
 
We've all been there. My advice would be to practice and perfect the dimpling, and then finish the part and move on. In a few years when you are finishing things up, go back and look at it and decide if you really want to re-do it. If so, it will be no sweat.


Chris
 
Palamedes said:
Thanks everyone! I very much appreciate your input and will research/try to do better.

How will the current under dimpling affect the final aircraft? is it doomed at this point or is this just cosmetic?
Click to expand...

rvbuilder2002 said:
No need to be worried....
It is fully acceptable from an airworthiness standpoint, just not to the finish quality that it could be.
Click to expand...


As I said earlier on, it is an appearance thing, not something that makes it unsafe.
I didn't mean to cause you stress... just teach.
I have been doing this for a long time, and have learned a lot in the process. Just trying to pass along some of that learning.
 
I have to agree with RV Builder 2002. You can see a depression around the dimple on your set rivets. Maybe the DRDT2 is not set up right. I had a similar problem with a homebuilt DRDT where the male dimple die was standing proud on the dimpling table and created dimples with depressions around the dimple. I switched to my C-frame/dimpling table and problem was solved. The problem was with the fact that the dimple die wasn't flush with the dimpling table. You can see this extra depression around your dimples. This isn't a structural concern - only cosmetic. Lay a steel rule on edge between driven flush rivets. It should lay absolutely flat - with no voids surrounding the rivet.
 
Parts that are back riveted, sure, they`re flat. But even with really nice dimples, it`s almost impossible to get it perfect when you`re riveting the wing skins to the ribs with a gun and bucking bar. Mines got some pillowing of the wing skin between the ribs. Used a C frame and hammer the get those dimples spot on too.
 
Another approach would be to find nearby experienced builders to take a look, and perhaps pass their experience along to you.

Are you building alone? If so, getting advice from fellow builders can result in a quantum leap in your final product.

Most builders are more than willing to help! :)
 
Well I'm glad this came up as I'm learning from it too. I ordered a DRDT2 after seeing how fast and easy it was for Jason in his videos. Or maybe that was the time compression...anyway it looked really fast :)
 
RayA said:
Well I'm glad this came up as I'm learning from it too. I ordered a DRDT2 after seeing how fast and easy it was for Jason in his videos. Or maybe that was the time compression...anyway it looked really fast :)
Click to expand...

Thats very much time compression =) Just be sure to load it correctly.. I'll work on it and post to this thread later, as well as make a video update about it down the road.

PCHunt said:
Another approach would be to find nearby experienced builders to take a look, and perhaps pass their experience along to you.
Click to expand...

Actually I have access to some great builders here locally through the local EAA chapter. I'll be seeking their advice for sure.
 
hayabusa said:
Parts that are back riveted, sure, they`re flat. But even with really nice dimples, it`s almost impossible to get it perfect when you`re riveting the wing skins to the ribs with a gun and bucking bar. Mines got some pillowing of the wing skin between the ribs. Used a C frame and hammer the get those dimples spot on too.
Click to expand...

I somewhat agree, but if you start out with less than ideal dimples, the finish quality is just that much worse.

Pillowing between wing ribs can be caused by a number of other things (that would be an entirely different subject from this discussion). With good tools and technique, even wing skins can look nearly perfectly flat.
 
Palamedes said:
I'm still kinda upset with myself =(
Click to expand...

Don't sweat it. Like others have said, it's purely cosmetic. Most of us building our first aircraft aren't building award winners.

Half of my tail kit is underdimpled. I plan to vinyl wrap it anyway, and it's likely people won't even be able to notice at that point.
 
PCHunt said:
Another approach would be to find nearby experienced builders to take a look, and perhaps pass their experience along to you.

Are you building alone? If so, getting advice from fellow builders can result in a quantum leap in your final product.

Most builders are more than willing to help! :)
Click to expand...

I very much agree.

The majority of the time, if a first time noob builder finishes a exceptionally nice RV, it is usually because of a lot of involvement with numerous other builders via an EAA chapter, local builders group, etc.
 
No worries

Don't feel bad. I recently corrected a noobie for under dimpling thinking as my arrogant self, my dimpling superior. When I flipped my center fuse, I was humbled. Clearly I under dimpled and didn't catch it. When she flies, please don't look at the bottom!:D
 
DRDT-2

Palamedes said:
I use a DRDT2 dimpler.

Now you have me worried! What is wrong with it? Note; it might be the image..

Here is another close up of dimpled vs non-dimpled on the elevator.
IMG_1265s.jpg


The rivet's sit down in there perfectly. Its 100% smooth when you run your hand over the final product..
Click to expand...

It is hard to determine what is your issue is. However if the DRDT-2 is setup properly (the instruction manual explains how to set it up properly) and the faces of the dimple dies contact parallel then you will get as perfect a dimple as a C-frame. Some may say the dimple isn't as crisp as the C-framed dimple but after the rivets are set you can't tell the difference. If you don't have a good looking dimple using either a C-frame or the DRDT-2, then check you tool setup, method of using the tool, and inspect your dimple dies.

The end appearance of a rivet after it is set is a function of:

Dimple dies and dimple
Mushroom set curvature
Gun Air pressure used
Flow rate of the air at the gun
Type of rivet gun
Quality of the trigger on the rivet gun
Type of bucking bar used
Skill of the Bucker
Skill of the Shooter

If anyone has any questions about or issues with the DRDT-2 please email and I will be glad to help in anyway I can. [email protected]
 
I found when using my DRDT-2, it was very important to have the sheet metal completely flat across the surface of the dimple sets. Any tilt one way or the other would produce a slight imperfection in the resulting dimple. When viewed while standing back you could see reflections that showed the aluminum around the dimple was not flat.
 
Try another quarter turn or so on the DRDT-2 adjustment bolt and re-dimple a few of those. See if it makes a difference. I bet you will see it.
 
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