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  #1  
Old 12-29-2017, 08:20 AM
MElstien MElstien is offline
 
Join Date: Jan 2013
Location: Kinnelon NJ
Posts: 101
Default #8 Screw Substructure Countersink depth Section 16-2

Hello,

I could use some simple confirmation of the proper depth for this countersink.

I am checking my QB wings and found that the nutplates on the inboard top edge have not been attached. These take a #8 nutplates (all but 1 a double wing nutplate).

I drilled, deburred and countersunk the #40 rivet holes. I then drilled and deburred the #19 screw holes. I dimpled the most rear one per plans. The remaining get countersunk.

Using some scrap 1/8 bar, I countersunk the bar until the #8 screw sat flush. I then adjusted the countersink cage so the screw would then site 4-5 thousands deep as it states in section 5 of the plans. Using my test dimple sample, I found that that it did not nest nearly as well I wanted or expected. I tried fastening it together and did not like the results. It wasn't until I got to a .018 recess of the screw in the substructure that the two pieces nested and attached to any degree of acceptability. Is this normal for #8 dimple to countersink. It goes against VANS instructions. Pictures attached.

I realize the geometry of a dimple and countersink are different and a perfect nest will not be accomplished but I do not like the results using the VANS rules.



My test dimple



The two different countersinks One per VANs suggestions


One deeper but nests and fastens better, cleaner with minimum distortion


The shallower dimple (VANS specs) with fastened sample dimple. Notice how the pieces diverge




The deeper countersink with still some divergence but much more acceptable

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Michael
Builders Blog http://elstien.us/wordpress/
Northern NJ
RV-10 Builder
Tail Kit delivered 6-2013
Started building April 2014
Empennage completed
QB Wing and Fuse Delivered December 2015
Starting to complete QB wings on December 2017
Dues Paid through 2018
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  #2  
Old 12-29-2017, 01:25 PM
MElstien MElstien is offline
 
Join Date: Jan 2013
Location: Kinnelon NJ
Posts: 101
Default VANS response

I called VANs today and spoke to support. They are awesome!

They are sending the issue to "Proto" and will get back to me. In the meantime we suggested making a more elaborate test sample consisting of 3 holes in the .032 and 1/8 pieces and drilling, deburring and countersinking and then assembling to see what happens.

They felt strongly, like me, that the .018 recess was too deep but they also saw a potential problem with the shallower dimple. This issue is more cosmetic and not really structural. My main concern is a pillowing effect between holes if the countersink is too shallow or the pieces having a gap between them if to shallow. They mentioned don't go more than 0.007-0.010 deep on the recess.

I will post pictures when the test is complete. The final result really wont be seen until I get to section 44. I am currently on section 16. We both agreed that I should only countersink as recommended by VAN's and make a note on section 44 to check depth and adjust at that point if needed.
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Michael
Builders Blog http://elstien.us/wordpress/
Northern NJ
RV-10 Builder
Tail Kit delivered 6-2013
Started building April 2014
Empennage completed
QB Wing and Fuse Delivered December 2015
Starting to complete QB wings on December 2017
Dues Paid through 2018
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  #3  
Old 12-29-2017, 01:45 PM
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9GT 9GT is offline
 
Join Date: Jan 2010
Location: Southern Michigan
Posts: 1,421
Default

There is also a little "give" in the countersink cage, depending on quality. If you use too much pressure you can over-countersink, too little pressure and it won't be deep enough. I found that the ball bearing countersinks gave better countersinks that were more uniform. Practice on scrap to estimate how much pressure to use. I made up lots of dimple samples in various skin thicknesses and labeled them. Whenever I needed to machine countersink for a dimpled skin, I would test it on scrap and creep up on the proper depth deeded for a nice fit before I machine counter-sunk the actual part.
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  #4  
Old 12-29-2017, 02:09 PM
jibby212 jibby212 is offline
 
Join Date: Oct 2014
Location: Sarasota Fl
Posts: 104
Default

I have found it is the very top sharp edge of the substructure countersink that seems to be in the way of the slightly rounded shape of the dimple. I broke this edge by lightly sanding or in some cases using a wider angle countersink to brake the very top edge. I would have thought an aircraft tool manufacture would have come up with a tool for this by now.
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  #5  
Old 12-29-2017, 02:11 PM
rocketman1988 rocketman1988 is offline
 
Join Date: Jun 2010
Location: Sunman, IN
Posts: 923
Default Also

If the cage doesn't sit perfectly flat or is "rocked" while drilling, the counter sink will not be uniform...
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RV-10
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  #6  
Old 12-30-2017, 08:53 AM
MElstien MElstien is offline
 
Join Date: Jan 2013
Location: Kinnelon NJ
Posts: 101
Default Response from VANs

As promised, Vans called me back after their proto lab took a look. The response was that indeed, those countersinks would need to be deeper than the 5-7 clicks suggested in section 5 but try not to go too deep. He also suggested I try dimpling with a c-fame because the dimples would be a bit more crisp and possible nest better.

Last night I countersunk to 8-10 thousands and left a note that they may need to go deeper. That will be determined when I get to step 44.

I also mentioned to Vans, thanks to one post here, that if the interference is due the rounded portion of the dimple vs the sharp edge of the countersink, that someone should make a rounding tool. I tried rounding this out using a much larger drill but it did not help much.

Any machine shop/tool people want to try making a cutting tool with a #8 pilot hole, 100 degree countersink with a rounded shape starting at about 7 thousands deep? To be used as a substructure countersink when the top piece is a #8 dimple.
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Michael
Builders Blog http://elstien.us/wordpress/
Northern NJ
RV-10 Builder
Tail Kit delivered 6-2013
Started building April 2014
Empennage completed
QB Wing and Fuse Delivered December 2015
Starting to complete QB wings on December 2017
Dues Paid through 2018
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  #7  
Old 12-30-2017, 09:39 AM
rocketman1988 rocketman1988 is offline
 
Join Date: Jun 2010
Location: Sunman, IN
Posts: 923
Default Dimple

Before I started my build, I did literally dozens of nesting test with a properly set DRDT and a hammer strike dimpler.

I found that you do have to go a bit deeper to get the dimple to nest in the countersink. I also found no noticeable difference in nesting the dimple produced from either method. I did find that the dimples seemed to be far more consistent with the DRDT, IMO...
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Bob
Aerospace Engineer '88

RV-10
Structure - 90% Done
Cabin Top - Aaarrghhh...
Doors - Done
On Gear
290 HP Barrett Hung
ShowPlanes Cowl with Skybolts Fitted - Beautiful

Dues Paid 2017,...Thanks DR+
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  #8  
Old 12-30-2017, 11:09 AM
BobTurner BobTurner is online now
 
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Location: Livermore, CA
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Default

As others have suggested, make sure the dimple is ‘crisp’. Usually the die will leave a faint witness mark (circle) around the dimple. I cannot see one in your photo.
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