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1bigdog

Well Known Member
I'd like to get away from the discussions where there was debate on what individuals do and want to find out how "It" should be done.

I was riveting the skins to the rear spar to complete the HS today. What I was finding is that the skins would not seat flush to the spar. The dimpled skins squeeze into the dimpled ribs perfectly of course, but the spars are countersunk so they have no give.

The "book" say if the skin is dimpled 100 degrees then to match this properly the spar should have a 112 degree countersunk hole. Not having a 112 degree countersink I did the obvious and re-countersunk the spar for a snug fit of the dimpled skin when squeezed, using a .002 feeler as my gauge for correct spacing between. Prior to re-countersinking there was no way to properly seat the skin to the spar and you could run the feeler all the way around.

Am I misunderstanding how it should be done ?? I am planning to find a 112 degree (or so) countersink so when I do the rest of the major countersinking it will sit correctly. Is this not the correct approach?? Otherwise you end up with a minimal radial contact point on each dimple.

Sorry for the long description. I don't see this as a place to compromise.
Thanks for all the expert opinions..

Michael B.
2014-15 Contributor
C-FWMB (Reserved)
 
.007 does it

Apparently I missed the part in the construction manual that states .007 below flush for dimpled skins to make with countersunk surfaces. It just begs the question why no one seems to sell a 112 degree countersink, although there are substructure / tank dimples.

Cheers.

Michael B.
 
Countersinks

I use tokens made from scraps of various thicknesses. Each set has holes in one end and dimpled holes in the other. One of each size dimpled token per thickness.
I suspect a large number of RVs are built with standard cutters.
 
I do not mean this in a negative way, but do a search on this topic - you will find volumes. If DR got a donation every time this topic comes up...

As Wirejock said, a token and experimentation is the best method.
 
it's not negative

Jon

Didn't take that in a negative way at all. I did an extensive search but what I found seemed more like individual practices rather than what should be done.

And as wirejock commented as well I did use scrap pieces to determine how much to further countersink from flush and "accidentally" arrived at the same conclusions. I started at about .005 further sunk and then applied a test rivet. Ended up with a couple additional clicks. What I didn't do is cut the scrap mating but it was very clear when things mated. Now I just have to order the Alodine pen since I've scraped off the alodine from all the spar holes.

So now that I've added this post I guess I have to mail a bigger donation to DR. It all worked out well.

Cheers.

Michael B.
 
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