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Countersink holes

Ron B.

Well Known Member
Haven't gotten very far and already have a question. On page 11-03, figure 2 (and actually step 2, Machine countersink all #40 holes indicated in figure #2), an arrow points out seven holes to be countersunk. I would say they are to rivet the ribs in each location before skins are mounted. These rivets will be under the tank skins when the tank is installed. My question is shouldn't the holes on the bottom spar flange corresponding with the same ribs be countersunk as well?
Thanks Ron
 
Rib holes

I went through this same step today and had the same question. I found the step in sect 12 where the ribs are riveted on and it's not 100% clear either. But it seemed like the most logical thing to do so I went ahead and counter sunk. Glad I was right.
 
You guys are a little ahead of me......

I got to this step tonight and have the same issue, but would like clarification please.

Q#1:
As indicated on p.11-03 step 2, we are to countersink the top seven holes as indicated in figure #2, labeled "countersink", so these holes get sized for the Ad3 rivets, not the deeper hole for the skin dimples -- or that's what I understand it to mean.
Per the thread, the bottom seven also get countersunk, and I am assuming sized for the ad3 rivets and not the skin dimples?
Q#2:
Referring to p.11-04 these 14 holes, 7 top and 7 bottom are not marked, indicating they are skin and or rib attach holes thus indicating they be countersunk to the deeper depth for skin dimples. I've already counter sunk the top 7 to the rivet depth, but as these two drawings appear to be in conflict, I wanted another opinion before working on the bottom 7. I am guessing these (all 14)are used for just the rib attach points and not skins, so I am guessing they be drilled to the rivet depth, thus figure 2 on p. 11-03 is incomplete and p.11-04 indicates in error these holes be drilled to the deeper depth?
Q#3:
Again p.11-04, all holes not otherwise indicated, get countersunk to skin dimple depth (flanges only)?
 
Q # 1 These 14 holes are to rivet the main spar to their respective ribs. Page 12-07 step 5 . They are to be countersunk for the 426AD3 rivet head only.
Q # 2 No skin here just rib and spar.
Q # 3 Flanges only and note the inboard skin is .032 " where as the outboard skin is only .025" thick. Different dept countersunk.
 
Countersinking whoos

Just thought I would pass this problem I encountered along and maybe help someone down the road. I countersunk the flanges of the rear spar for it's respective skin thickness, or so I thought! It turns out that at both W-1007D and the W-1007E backing plates the counter sink depth was not deep enough. Using the same setting on the countersink cage, all along the rear spar flanges where the outboard skin sits gave a shallower depth at the doubler plate locations then everywhere else for some reason. Look behind after the skins are clecoed in place for a tight fit before riveting.
 
Thanks Ron

Q # 1 These 14 holes are to rivet the main spar to their respective ribs. Page 12-07 step 5 . They are to be countersunk for the 426AD3 rivet head only.
Q # 2 No skin here just rib and spar.
Q # 3 Flanges only and note the inboard skin is .032 " where as the outboard skin is only .025" thick. Different dept countersunk.

I'm with you.....
 
Countersink Depth ?

Am I misunderstanding the countersink math - I flush set an 426AD3 rivet head and then added .010 in depth to the micro countersink (10 clicks), this was the method described in section 5 ?

How do most builders figure out the depth the countersink depth?
Is there an mathematical method I am not aware of?

First time builder

Thanks Mike
 
I had the same question....

Am I misunderstanding the countersink math - I flush set an 426AD3 rivet head and then added .010 in depth to the micro countersink (10 clicks), this was the method described in section 5 ?

How do most builders figure out the depth the countersink depth?
Is there an mathematical method I am not aware of?

First time builder

Thanks Mike

I used the same reference you did in sec 5 and countersunk the skin holes 10 clicks deeper than a flush rivet. I also shot the question to vans and got an interesting reply- basically vans have had several builders apparently drill too deep into the spar, so they suggested to me to drill the skin holes at the same depth of the rivet holes with just some additional pressure. They went on to say the skins fit the smaller holes just fine.
I had already drilled one of my spars using the deeper set at 10 clicks, I use significant pressure every time I drill so I feel pretty sure the difference is really close to .010 as specified, so I'm not too worried I screwed the pooch and Vans said I was ok.
I'm going to drill the right spar with the smaller rivet sized holes just to be sure I don't go too deep.
Bottom line, I think either is ok, as long as you don't go any deeper than .010 from flush - but consider my advice in the light from a fellow 1st timer too!
:)
 
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