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  #1  
Old 11-25-2018, 12:40 PM
hubbardr1 hubbardr1 is offline
 
Join Date: Apr 2008
Location: Olathe, KS
Posts: 7
Unhappy Too Deep! Counter sinking the Rudder trailing edge

After getting the rudder ready for priming I went ahead and moved forward to the elevator. The elevator trailing edge wedges went much smoother and much more uniform. So I decided to take a second look at the rudder wedge and I'm worried. I'm pretty sure I overdrilled the rudder trailing edge wedge counter sinks too deep.

The top wedge in these photos is the rudder wedge. Bottom is from an elevator. The rudder depth from top of rivet head to the top of the skin is about double that of the elevator. :/
https://photos.app.goo.gl/wX2FbRErybJMMafu8

You can also see where I pulled the drill press too hard and slightly deformed the wedge edge. I'm worried once riveted, the trailing edge will resemble a missouri road vs something nice flat and and straight.

So what are my options? I've contemplated re-doing the rudder wedge but I've already dimpled the rudder skins. Seems impossible to get the hole alignment right now that its dimpled.

Anyone out there redo the rudder wedge? Successful? Other ideas?
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  #2  
Old 11-25-2018, 01:45 PM
Ralph Inkster Ralph Inkster is offline
 
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Location: Calgary, Alberta
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Sandwich the wedge between the skins & see if they are too loose, if excessive you would have to get another wedge & try again. You are looking for no gaps between the materials. In your pictures it looks like the countersinks might actually have to be deepened a bit further. Just buff the press marks smooth.
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  #3  
Old 11-25-2018, 04:24 PM
hubbardr1 hubbardr1 is offline
 
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Location: Olathe, KS
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Quote:
deepened a bit further
!!! Phew. Here I am thinking I went too deep. So you are saying that even the top wedge might not be deep enough? Meaning the bottom wedge surely isnt. Hum. I think I'll get a better dimpled sample skin to test those with and double check. Better to take more off than try to figure out how to add more back in. Thanks Ralph!
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RV-10 Emp Kit ordered at OSH'18
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Happy to provide opinions on what not to do.

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  #4  
Old 11-25-2018, 04:25 PM
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Brantel Brantel is offline
 
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Location: Newport, TN
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Quote:
Originally Posted by Ralph Inkster View Post
Sandwich the wedge between the skins & see if they are too loose, if excessive you would have to get another wedge & try again. You are looking for no gaps between the materials. In your pictures it looks like the countersinks might actually have to be deepened a bit further. Just buff the press marks smooth.
Newish guidance from Vans does not agree with the traditional wisdom on countersinking. It is much more conservative around depth.

The limits are called out in section 5 of the manual.

Just eyeballing the pictures, the deep ones are very likely too deep according to Van’s.
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Last edited by Brantel : 11-25-2018 at 04:31 PM.
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  #5  
Old 11-25-2018, 04:30 PM
hubbardr1 hubbardr1 is offline
 
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I'm open to "newish" guidance as well. What is latest?
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  #6  
Old 11-25-2018, 04:43 PM
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Brantel Brantel is offline
 
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Quote:
Originally Posted by hubbardr1 View Post
I'm open to "newish" guidance as well. What is latest?
Flush - 0.007” section 5 in the manual.
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RV-10, #41942, N?????, Project Sold
---------------------------------------------------------------------
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Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
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  #7  
Old 11-25-2018, 05:20 PM
hubbardr1 hubbardr1 is offline
 
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I've read it and missed that. Thanks!
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Happy to provide opinions on what not to do.

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  #8  
Old 11-25-2018, 06:02 PM
leok leok is offline
 
Join Date: Apr 2013
Location: Clarkston, MI
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Default Correct countersinking depth

When countersinking you have to think through what you are trying to accomplish. The depth is different when placing a rivet only, or when placing a skin and then a rivet.
When a skin has to fit in a countersink, you need to take the thickness of the skin into account. You will have different thicknesses of skin needing to fit into countersinks. Here is how you do it.


Find a small tab of material of the same thickness as the skin at the location. Drill and dimple the tab. You now have a gauge. I make the tab large enough to write down the thickness of material on it. You will end up with several throughout your build.
Using a piece of thick scrap, drill and countersink the scrap until the gauge just fits flush with no gap in the countersunk hole. Now you are ready to countersink the part.


The rivet will fit nicely in the dimple. You need the dimple to fit nicely in the countersink.
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  #9  
Old 11-25-2018, 07:14 PM
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Brantel Brantel is offline
 
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Quote:
Originally Posted by leok View Post
When countersinking you have to think through what you are trying to accomplish. The depth is different when placing a rivet only, or when placing a skin and then a rivet.
When a skin has to fit in a countersink, you need to take the thickness of the skin into account. You will have different thicknesses of skin needing to fit into countersinks. Here is how you do it.


Find a small tab of material of the same thickness as the skin at the location. Drill and dimple the tab. You now have a gauge. I make the tab large enough to write down the thickness of material on it. You will end up with several throughout your build.
Using a piece of thick scrap, drill and countersink the scrap until the gauge just fits flush with no gap in the countersunk hole. Now you are ready to countersink the part.


The rivet will fit nicely in the dimple. You need the dimple to fit nicely in the countersink.
That's the way I built my RV-7 and many many other airplanes have been built over the years but it does not agree with Van's current advice on the subject. If you do it the old fashioned way, your countersinks will be deeper than what Van's currently recommends.

I was advised by Scott of this new to me recommendation here:

Quote:
Originally Posted by rvbuilder2002 View Post
Hi Brian, I noticed on your blog you mentioning your countersink depth of .012-.015" deeper than flush compared to Van's recommended of .007 deeper. The .007 deeper is based on detailed analysis of riveted joints after sectioning them, polishing them, and inspecting under magnification. The error that people make by working to a depth that allows the skin to lay 100% flush is that they forget that on the the cross section shape of the dimple has a small radius where the skin is reformed to make the dimple, but the machine counter sink has a sharp corner. It is the interference of this radius on the sharp corner that you are compensating for in order to get the skin to lay 100 % flush. Doing so results in a gap between the sides of the dimple and the countersink that is clearly visible in the sectioning tests I mentioned. The finished appearance as far as how it looks on the exterior between the two countersink depths is indistinguishable, but the long term integrity could be compromised which is why Van's recommends no more than .007 deeper for dimples into countersinks.


There are a few more post by Scott in the archives that give the detail behind this current recommendation....
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RV-10, #41942, N?????, Project Sold
---------------------------------------------------------------------
RV-7/TU, #72823, N159SB
Lyc. O-360 carbed, HARTZELL BA CS Prop, Dual P-MAGs, Dual Garmin G3X Touch
Track N159SB (KK4LIF)
Like EAA Chapter 1494 on Facebook

Last edited by Brantel : 11-25-2018 at 07:16 PM.
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  #10  
Old 11-25-2018, 08:36 PM
TASEsq TASEsq is offline
 
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I've always wondered if instead of countersinking deeper to compensate for the edge radius of the dimple, if you could get a wider, shallower countersink tool and chamfer the top edge off the countersink to account for the radius? (never seen such a tool).

I've definitely seen than a C-Frame makes a sharper dimple than the DRDT2, and these skins sit better in a shallower countersink, in my opinion.
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