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Countersinking the main spar skin rivet holes

NorthernRV4

NorthernRV4

Well Known Member
I am ready to countersink the skin rivet holes in the main spar flange on my -4 spars and I'm going in circles on whether to machine countersink or dimple countersink the holes. Tech Support said it wouldn't matter from a structural standpoint to do it either way. I've already dimpled my aft spar flanges with good results but I can't really comment about possibly distortion since I have not mated my wing skins (yet to be dimpled) to them again.

I'm leaning toward dimpling the main spar flanges (.040") with my pneumatic followed by a hand squeezer to crisp them up. If I need to touch them with a microstop after that to remove a thousand or two then I can. The main reason I'm leaning this way is that I find the skin dimple nests into a dimpled substructure better than a machine c/s even when machining .006-.007" deeper than flush as per Van's instructions. The newer kits are all thicker flanges so dimpling is out of the question and there is many a thread about machine c/s these.

Anyone have some advice?
 
NorthernRV4 said:
I am ready to countersink the skin rivet holes in the main spar flange on my -4 spars and I'm going in circles on whether to machine countersink or dimple countersink the holes. Tech Support said it wouldn't matter from a structural standpoint to do it either way. I've already dimpled my aft spar flanges with good results but I can't really comment about possibly distortion since I have not mated my wing skins (yet to be dimpled) to them again.

I'm leaning toward dimpling the main spar flanges (.040") with my pneumatic followed by a hand squeezer to crisp them up. If I need to touch them with a microstop after that to remove a thousand or two then I can. The main reason I'm leaning this way is that I find the skin dimple nests into a dimpled substructure better than a machine c/s even when machining .006-.007" deeper than flush as per Van's instructions. The newer kits are all thicker flanges so dimpling is out of the question and there is many a thread about machine c/s these.

Anyone have some advice?
Click to expand...

You wont be crisping up dimples in .040 with your hand squeezer. A properly functioning pneumatic squeezer will form a dimple in .040 much better than you can by hand.
If you choose to dimple, a better process would be to lightly machine countersink after dimpling to make the dimple slighter deeper to receive the skin dimple.
 
rvbuilder2002 said:
You wont be crisping up dimples in .040 with your hand squeezer. A properly functioning pneumatic squeezer will form a dimple in .040 much better than you can by hand.
If you choose to dimple, a better process would be to lightly machine countersink after dimpling to make the dimple slighter deeper to receive the skin dimple.
Click to expand...

True, even after hand squeezing the rivet head sits .007" below flush but it seems to flatten out the surrounding material a bit better, not quite sure why.

I guess I'm more concerned with the finish on the visible surface of the skins. I do plan on back riveting the top skins first and traditional bucking of the bottom skin rivets. I realize this is going to make bucking the aft spar more challenging since the flange faces forward into the wing but I want the topside to look as nice as possible. Seems like the depressions left from squeezing might show up more in the visible surface, if driving the rivets with a gun/bucking bar from the outside.
 
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