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VS-808PP Countersink

RVGator

Member
I am attaching the 808PP doubler to the 803PP rear spar. After counter-sinking the 808 doubler I clecoed it to the 803PP spar to check the fit. It appears the doubler is standing a few thousandths above the spar. Notice the lack of a gap between the right lightening hole and the spar and the presence of a gap on the left hole.

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I'm afraid to countersink any deeper before I get some advice. The countersink is already slightly deeper than the rivet itself. I expected that since it has to accept the dimpled spar. But I don't want to go any deeper until I check with the pros.
 
I don't have my plans with me...

If you've already countersunk to the point where your rivet is sitting in correctly, then it's probably not your countersink causing the pieces not to mate. Typically, when I run into this problem, I find a hole that I missed during the deburring process and a burr is causing the part to not sit correctly.
 
Check that you haven't underdimpled.

How deep are your countersinks, i.e. how many clicks beyond "rivet is flush"? IIRC I went about eight clicks further (.008").
 
Countersink is the same

I guess I'm lucky, I didn't count cliks but I eneded up .008" beyond flush as well.

I've carefully inspected for burrs and bad dimples. I dimpled with a pneumatic squeezer mounted in a vice so the dimples seem very consistent. I did notice that when I clecoed only the dimpled section (just the bottom rivets that are supposed to be flush), VS808 sat flatter - still not perfect- but better. Clecoing the rest of the doubler resulted in some lifting. The doubler does have a lengthwise bow in it. Also, the edges of the doubler where they extend past the spar flange appear nicely fitted. It's just around the lower 2 lightening holes that I have the concern.
 
Might be the spar web

I'm stumped. In this series of photos I add clecos to the spar and doubler.

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With each pair of clecos the spar web separates further from the doubler

DSC00607.jpg


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When I remove all but the end-most clecos, all falls nicely back into place.

DSC00611.jpg


Will this separation happen when I rivet? Is it the result of torquing from the cleco springs? The separation doesn't occur further up the spar.
 
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What happens if you use a spring clamp or c-clamp (or similar) to clamp the parts together in addition to the clecos? If the gap goes away with a little more clamping pressure, then clamp them back together before you rivet and pound away.

My guess is the 808PP doubler is not perfectly flat and is contacting the 803PP spar at the edges where the clecos sit. You're seeing the apex of the slightly curved doubler causing a gap at the lightening holes.

Could that be what's going on?

To verify, you could turn the doubler over on the spar (so that the surface you see in the photos is then sitting against the spar). If the gap goes away then the doubler is slightly warped (of course now the gap should be at the edges, where the clecos are. Wouldn't surprise me the way these parts are stamped out.
 
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That's what I thought...

I tried that and it all fit perfectly.

I can squeeze the parts back together. But if I have cut my countersinks a few thousandths too deep will I have a weakpoint?

Vans emailed and said they saw nothing wrong with any of the fit. Unfortunately I've been unable to get a good picture to send.
 
Dave,

A few thousandths deep won't be a problem. Just make sure the countersunk material isn't knife-edged.

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Get the parts clamped together as firmly as you can and rivet. Any load transfer occurs only at the rivets, so as long as there's not a gap at the rivet locations the joint will carry the designed loads.

BTW, looks like you're doin' great!
 
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Thanks for the help...

Vans reminded me in an email that I am not to expect machinist tolerances for these parts. I checked for a knife-edge and the countersinks are fine. Thanks for reminding me of that one too. The build went easy.

DSC00612.jpg


VS will be done tomorrow. This forum is quite a resource! Moving on...
 
I have a ?....

.... in the pic in post # 7 what is the rivet hole just above the 2 lightening holes? I have one on mine as well, and I can't figure out what it is for. It is not in the plans anywhere. Is it just to draw the 2 parts together better or is it used in a later stage of the build?

Thanks

Chris
 
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