inboard ribs to main spar

vickruis · Post by **vickruis** » Tue Feb 06, 2007 8:01 am

After rivetting some inboard ribs to the main spar I noticed that around the rivet you can see some cracks, as you can see on this picture:

At a certain angle you cannot see the cracks, but in this picture they are VERY visible.

Do I have a major problem now? In some messages I've read that this is caused by the hardness of the anodizing, and the softness of the inner aluminium, but I'm not sure if this is harmful. Replacing the spar is not a job I'm looking forward to...

[Edit by Spike: Fixed the image. "Disable BBCode in this post" was accidentally turned on.]

Post by **Spike** » Tue Feb 06, 2007 8:43 am

Welcome to RB

Glad to have you stop in.

The cracking that you are showing there is perfectly normal. Most all of the spars that have been annodyzed do that. Mine did. Carry on!

- Spike

cjensen · Post by **cjensen** » Tue Feb 06, 2007 2:49 pm

Yep, totally normal. The anodizing creates a very brittle surface layer that will show radial cracks around shop heads. You can stop holding your breath now, and keep goin!

(BTW...the pic isn't working for me...)

Post by **Spike** » Tue Feb 06, 2007 3:35 pm

Yeah, looks like it was taken down off of its server.

vickruis · Post by **vickruis** » Wed Feb 07, 2007 12:42 am

Luckily I only had to hold my breath for a few hours. And the pic is up again.

captain_john · Post by **captain_john** » Wed Feb 07, 2007 6:47 am

...what they said.

They look well shaped, but if I were to criticize... maybe a tad overdriven.

Certainly NOT drillers, though!

Nice work!

CJ

TomNativeNewYorker · Post by **TomNativeNewYorker** » Wed Feb 07, 2007 3:55 pm

If those where on the planes I work on at work, I would be stop drilling the cracks and putting a lap patch repair doubler on it.

Post by **Spike** » Wed Feb 07, 2007 3:58 pm

How do you stop drill a few hundred tiny cracks in the coating?

cjensen · Post by **cjensen** » Wed Feb 07, 2007 4:01 pm

TomNativeNewYorker wrote:If those where on the planes I work on at work, I would be stop drilling the cracks and putting a lap patch repair doubler on it.

Not sure what you are seeing Tom. These are not cracks in the AL. They are cracks, but only in the anodized surface. Nothing structurally wrong here.

TomNativeNewYorker · Post by **TomNativeNewYorker** » Wed Feb 07, 2007 4:47 pm

OK gotcha, looked like cracks in the metal from the picture posted.

Wicked Stick · Post by **Wicked Stick** » Wed Feb 07, 2007 9:52 pm

Perhaps it might be possible to reduce the anodize cracking by setting the pressure of the gun slightly higher and bucking them using less time. In theory, the more/longer you buck, the more you work-harden the rivet.

Even squeezing them sometimes causes the formed head to produce those spider/stress cracks on the anodized surface.

If you have the rivet gauges handy, check them to see if they fall in between the tolerances for that size rivet. It's my opinion that if the bucked rivet has to lean towards one side of the range, let it be slightly overdriven than underdriven.