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  #1  
Old 09-01-2018, 06:25 PM
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Strikefinder Strikefinder is offline
 
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Default Countersinking Wing Spar Flange

Hi all,

I've just finished up inventorying my wing kit and I'm setting up a jig to start installing platenuts on the wing spars for the tank skin attachments and access plates.

I admit I'm a bit apprehensive about this step--it seems like there's a fair amount of opportunity to screw it up, so I was hoping I could run my thinking past the group to make certain I'd assimilated everything I need to know:

1. I've read through "Drilling Recesses for Tank Screw Dimples" from the RV-ator 2005 1st, and know to "countersink until the top of the screw is level with the surface, then go two clicks deeper on the microstop. The actual outside diameter of the countersink measures .365-.375. I know this might be somewhat smaller than a hole you'd get if you took a sample piece of aluminum skin and dimpled it for the hole.

2. I was leaning toward using the technique described here: http://www.vansairforce.com/communit...ad.php?t=2740; basically, using aluminum angle as a mechanism to center the pilot for the #19/#28 pilot countersinks. Should I have this bar in place to do the #40 holes as well? Any reason why I shouldn't use this technique and use the platenuts with a #30 pilot as per the directions?

3. Once I have the holes, how does everybody spot prime them? Alodine pen seems to be the cleanest method...another $100 in the hole unless I can come up with a better idea. Should I use the Alodine pen on the #40 countersinks, even though there will be a rivet? Better safe than sorry?

Is there anything big I'm missing/should consider before I start going down this road? I appreciate any further pointers before I boldly go where everybody else has gone before...
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  #2  
Old 09-02-2018, 12:10 AM
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nzrv8 nzrv8 is offline
 
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I also agonised over this. I just finished my spars, and I tried both methods of countersinking - the angle to back up the screw hole, and the Van's method of using the platenut to guide the countersink bit.

I found the Van's method worked perfectly and it was faster than using the angle. The countersinks are clean and chatter free.

Regarding the diameter of the countersink - I tried using the various diameters published on VAF, but in the end I found it easier to use a piece of dimpled scrap to check the depth of the countersinks, rather than using a measured diameter. There may be some slight diameter variance between dimples created using different brands of dimple dies, I'm not sure - but it would be best to dimple a piece of scrap using your dies, and start off slow, sneaking up to your final diameter. Make sure you are clamping the test dimple firmly to ensure it is nested properly into the spar.

One thing to note is the screw countersinks will end up very slightly knife-edged, which I understand is normal for this area of the build.

The #40 holes were straightforward, there is plenty of meat left in the thick spar flange to guide the countersink bit. Make sure the rivets here sit completely flush with the top of the spar flange, a couple of mine sit a touch proud and I'm not sure how this will affect the skin fit.

I spot primed all countersunk holes with etch primer and a q-tip.

Overall it was straightforward and enjoyable. Take your time and keep checking depth every few countersinks, and you'll be fine. It is also worth taping up the gap between the spar reinforcement plates and the flange so swarf doesn't get in, it would be difficult to get out afterwards.

If you want any photos, feel free to PM me!

Hugh
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  #3  
Old 09-02-2018, 04:26 AM
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I made a jig out of 0.125 aluminum stock. Details here. I was very pleased with the results.
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  #4  
Old 09-02-2018, 05:51 AM
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Practice on scrap first.
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  #5  
Old 09-02-2018, 10:50 AM
Robin8er Robin8er is offline
 
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This is the first of many "well if have to do it or it will never get done" cuts. This is the warm up for the canopy, cowl, rear wing spar to fuselage etc. While you may get a little chatter on a few holes, if you are making a legitimate effort you cant really screw it up. If you mess up more than 2 holes, stop and rethink what you are doing.

The techniques described above are all good. I just used a single piece of steel with a hole drilled into it and clamped it to each hole as I was countersinking. It prevents chatter from the bit. It works fine. Your method you have posted will work just fine as well.
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Old 09-02-2018, 10:56 AM
David Paule David Paule is offline
 
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For priming the countersinks, I used rattle can primer, shot a little into the cap, and used a Q-tip to dab them. Fast and easy.

For drilling them, I used a platenut for a jig, replacing it often (and later riveting these on) and a bit of scrap for a pilot-centering guide. To hold the scrap, a Cleco side-clamp worked well.

And another piece of scrap that I'd dimpled, made a good guide to depth. A little deep, perhaps, but it clearly worked.

Dave
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  #7  
Old 09-09-2018, 08:13 AM
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All:

So I've started to chip away at this and in general it's going pretty well. The #40 countersinks are pretty straight forward and I've tried just using the Vans method of using the platenut as a pilot guide, and I think I'm just going to do that.

What I'm a bit confused on is the depth of the #8 screw countersink. I set up the cage to go flush + 2 stops, and the sawed off screw head sits just under flush (I'll try to get a pic later). When I measure the diameter (with two different sets of calipers), I end up with a diameter of about 0.32". I have a dimpled piece of 0.032 that sits a bit proud, but I'm under the impression it shouldn't be totally flush (see http://www.vansairforce.com/communit...d.php?t=117935).

So, technique wise, I think I'm pretty comfortable at this point (thanks for the feedback). However, I'm not sure if I should go deeper than I have, since flush + 2 clicks seems like Vans advice, and I don't want to go too deep. However, I've still got 0.04" of diameter before I reach Vans recommendation, and though I expect the skin to sit a bit proud, I figure there's no reason for it to sit more proud than necessary. Any thoughts?
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  #8  
Old 09-09-2018, 11:18 AM
Robin8er Robin8er is offline
 
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Mine were slightly proud, but when screwed/riveted down it sat flush. Try installing a screw and see how it looks.

Don't be in a rush, you can always go slightly deeper later in the build if you realize its not deep enough when you install the skins.
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