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02-22-2013, 11:38 AM
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Join Date: Nov 2009
Location: Yardley, PA
Posts: 1,334
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Dimples
I agree, the dimples dont' look right. Are you using a DRDT-2? I've had better results with a C-frame dimpler that you smack with a hammer.
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02-22-2013, 01:52 PM
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Join Date: Aug 2012
Location: Chatham Ont.
Posts: 41
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Thanks To All
Mike
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02-22-2013, 04:40 PM
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Join Date: Apr 2009
Location: USA
Posts: 1,499
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Mike,
An hour with Tom will make all the difference in the world. We can talk about pressures, angle to the dangle, how to hold your mouth right, 2X or 3X, back riveting sets, tungsten bucking bars, riveters tape, tank dimple dies, primer application and metal temperatures, but nothing helps quicker than getting with someone who has built one. Enjoy the build.
__________________
Good judgment comes from experience, and a lot of that comes from bad judgment.
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02-22-2013, 08:58 PM
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Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 1,558
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Mike,
Your skin looks normal for rivets set with a rivet gun. As others have said, if you can back rivet, you'll see a difference. I just finished my wing top skins on my RV14, one done the normal way and one back riveted and the difference is noticeable - but I think once it is painted, you won't notice the difference as a casual observer. I had help with back riveting - from experienced builders. Structurally, there's no difference. Also, as others have said, too much air pressure to set a 326-3.5 rivet will produce more skin deformation than is necessary, ask me how I know. I use about 55 psi with 75 feet of small diameter hose coming off the compressor (some pressure loss) and don't press hard with the gun, whether using a flush set or a back rivet set.
__________________
SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019 Flying
Cincinnati, OH/KHAO
JAN2020
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02-22-2013, 10:05 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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All of the riveting tips given so far are helpful, but I think riveting technique is causing only a small part of what you are seeing and are not happy with.
The lack of flatness evident while using a span wise straight edge on the skin could be caused by a number of things.
The most common is not having the bend angles of the flanges of the wing ribs adjusted to 90 degrees.
This will try and force the skin out of plane/alignment.
BTW, the photo with the straight edge is not really indicating an unusual amount of waviness in the skin. I have a feeling you are checking because you don't like how the riveted areas look. I think that is probably being caused by something else....
In the third photo in your original post, it is obvious that the dimples on the skin are not fully formed.
With experience this can easily be detected using the skin reflection.
In that photo, there is a reflection of a gray hose or extension cord on the floor. Note where it comes out from under the foot and intersects through a dimpled rivet hole. The reflection is all distorted as it passes over/through the hole. It is indicating that there is an approx 1 " diam. dished area in the skin around the hole. This is a classic indicator of a not fully formed dimple. It appears most of the dimples on the skin look the same. If a dimple is formed correctly on a flat skin (this skin was flat until it was clecoed to the wing frame), the skin will still be perfectly flat right up to the edge of the dimple (before riveting)
If you already have dished areas in the skin at each hole before riveting, once you rivet (regardless of how skilled you are), it will only get worse.
I would suggest that you remove the rivets (please get some experienced help to teach you if it is your first time), and re-dimple the skin.
This time look carefully at the reflection of overhead ceiling lights in the skin while it is on your dimpling table. There should be no distortion of the reflection in the area around a properly formed dimple. Re-dimple a hole out in the middle of the skin (If you are using a C-frame tool, don't be afraid to hit it hard... if using something else, it is not adjusted/working properly) and compare the light reflection to the others near it. I think you will quickly see the difference.
Post back about how it goes, or if you have any questions.
Last edited by rvbuilder2002 : 02-22-2013 at 10:35 PM.
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02-22-2013, 10:27 PM
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Join Date: Sep 2012
Location: Omaha, NE (KMLE)
Posts: 2,247
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What kind of hammer do y'all recommend for the C-frame when dimpling? I just used what I had handy -- a 16 oz (or maybe 32, I don't remember off hand) plastic dead blow. One good whack seems to do the job.
__________________
Dale
Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
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02-22-2013, 10:46 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by DaleB
What kind of hammer do y'all recommend for the C-frame when dimpling? I just used what I had handy -- a 16 oz (or maybe 32, I don't remember off hand) plastic dead blow. One good whack seems to do the job.
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What hammer you use is far less important than knowing how hard to swing the one you are using.
Probably just about any hammer can work, but some will take more effort and/or more hits to get a properly formed dimple.
The work surface the the C-frame tool is resting on is also a major factor.
If you have it sitting on a concrete floor (very solid, unyielding surface), it takes a lot less energy to make a crisp, well formed dimple, than if you have it resting on a lumber framed particle board work table.
The key is to learn how to tell when the dimple is formed properly, and then adjust your technique to repeat that consistently with what every set-up you are working with.
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02-23-2013, 07:51 AM
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Join Date: Nov 2009
Location: Yardley, PA
Posts: 1,334
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Quote:
Originally Posted by DaleB
What kind of hammer do y'all recommend for the C-frame when dimpling? I just used what I had handy -- a 16 oz (or maybe 32, I don't remember off hand) plastic dead blow. One good whack seems to do the job.
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Dale,
On my C-frame set-up I use the plastic (looks like polyethylene) head hammer that it came with, but I agree with the previous poster, knowing how to use it is more important. Using light multiple strikes with the hammer lets me listen to each blow - the sound of the second blow is much different (more solid sounding) than the sound of the first since the first blow is doing most of the dimpling. If the third blow sounds identical to the second, then I know there is no more dimpling left to do; if not, a 4th strike will usually do it.
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02-23-2013, 07:57 AM
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Join Date: Sep 2012
Location: Omaha, NE (KMLE)
Posts: 2,247
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Quote:
Originally Posted by Av8torTom
Dale,
On my C-frame set-up I use the plastic (looks like polyethylene) head hammer that it came with, but I agree with the previous poster, knowing how to use it is more important. Using light multiple strikes with the hammer lets me listen to each blow - the sound of the second blow is much different (more solid sounding) than the sound of the first since the first blow is doing most of the dimpling. If the third blow sounds identical to the second, then I know there is no more dimpling left to do; if not, a 4th strike will usually do it.
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Hmmm.
I give it one good solid whack and the dimples appear to be fully formed, well defined, and with a distinct ring around them just like if I'd done them with a squeezer. I can't tell the difference between a dimple smacked once, and one I've hit twice. So I guess they're getting done OK.
I know you can under-dimple, but I've wondered if it's possible to over-dimple when using dimple dies. Other than beating on them hard enough to stretch the metal, I can't see how you could.
__________________
Dale
Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
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02-23-2013, 09:19 AM
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Join Date: Jan 2005
Location: Ontario, Canada
Posts: 1,544
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Dimple a row of holes. Now hold the metal/sheet in front of you and slowly rotate it in front of your eyes so that the sheet is flat directly in your view. If the dimples are done properly they will appear to disappear and the sheet will look perfectly flat with no distortion.
Test this by purposely under dimpling a row,now take a look. Then hit them one more time and check again. Continue this too many times and you will go too far and the distortion will come back as you stretch the skin around the hole.
Once you get the right number of hit/hits you will always get it right. I use a small ball peen hammer, tap,tap, whack, done.
__________________
Tom Martin RV1 pilot 4.6hours!
CPL & IFR rated
EVO F1 Rocket 1000 hours,
2010 SARL Rocket 100 race, average speed of 238.6 knots/274.6mph
RV4, RV7, RV10, two HRIIs and five F1 Rockets
RV14 Tail dragger
Fairlea Field
St.Thomas, Ontario Canada, CYQS
fairleafield@gmail.com
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