J

JoeLofton

Well Known Member
I'm to the point of countersinking my main spars for attachment of the wing skins. Per the instructions, I made a dimpled test patch to check for the correct depth of the spar countersink. Before drilling away into my golden spars, I tried the method on a piece of scrap angle.

It appears that the countersunk hole has to be made unreasonably large (and deep) to get the test patch to fit flush. I started with a countersink in which the rivet would sit flush (as my reference), and went all the way to 12 clicks deeper on the microstop - and the test patch dimple still didn't fit all the way into the hole. The holes are for #3 rivets, and I used the correct dimple dies in a Main Squeeze to make the test dimple.

Does anyone know of a better (more accurate) way to set the countersink depth? Does the skin dimple have to fit all the way into the spar countersink before riveting, or does riveting pull the dimple deeper into the countersunk hole? :confused:

Thanks for your help.

Joe Lofton
RV-9A Wings
 
is this legal?

I got tired of chasing that around also, so I changed my method. The outer dimple surface that nestles into the countersink is the same surface "theoretically" as the cavity in the female die. So I put a rivet in the female die temporarily to gauge how recessed the rivet head is below the surface of the face of the die. I then set the countersink depth so that a rivet placed in the countersink is recessed the same amount as with the rivet in the dimple die.

Thus verily the two cones should match perfectly in a theoretical world.

At least it keeps me from oversizing the countersink hole.

Anyone else tried this?
 
There are a lot of different ways to define "fit" in this context. Is the dimple mostly in there? Can you see daylight between the layers? Et cetera. I never was sure what Van's wanted. I thought I read that Van's got tired of trying to define it, and started publicizing a new technique for doing this recently -- was it "1 or 2 clicks"?

My airplane was mostly built by the time they made this change. I too was using something like 10 clicks more than flush. Of course, your countersink cage may vary from mine...

One thing to watch for is that your test-patch dimples might not be "fully formed". It does make a difference -- there is a lot more waviness to the surrounding metal unless the dies are really smacked together.

Does any of this matter? I don't know. All I know is that when I tried comparing a riveted 10-click countersink joint to a 1-click countersink joint by cutting a cross-section with my bandsaw, there was no visible difference.
I suspect the metal bends and conforms quite a bit during the riveting process no matter what you do.
 
Do not use the dimpled test piece method for the wing tank screws. Van's changed their recommedation on this in one of last year's Rvators. They found that people who used the dimpled test piece method were often over-countersinking. If you do a search on this topic you'll see a number of posts that indicate the Van's suggested alternative. Good luck.
 
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