Stress crack in a #10 dimple ?

[Calvin25]

Please take a look at these photos. I have a stress crack from dimpling the bolt holes in the elevator that attach the counter weight.

Order a new part or drill?

If I drill can it be done in the dimple?
What should I use to fill the drill hole?

As always, thank you VAF.

[Kevin Horton]

If this was my aircraft, given how critical the elevator counterweight was, I'd scrap the part and buy a new one. Next time I'd drill the hole a bit bigger before dimpling it, as those large dimples force the material to stretch quite a bit, and the smaller the hole the more stretching there is.

If you really want to keep the part, I'd send the photos to Van's, and ask for an opinion from one of the engineers. No disrespect from the great guys handling customer support, but this is an area that deserves a review by an engineer who knows the loads this part carries, rather than a "looks great, build on" answer from someone who is just sticking a finger in the wind.

[vic syracuse]

I agree with Kevin's recommendations, but even if Van's says to keep it, I would be tempted to "stop drill" that crack with a number 50 drill, or anything you might have below a number 40.

Vic

[apkp777]

There's no question that the crack will grow. Get a new part. The piece of mind will be worth all the $$ and time. If that counter weight moves in flight you may have a serious problem.

That being said, you may drill a new mounting hole and the cracked one you can clean up with a uni-bit and remove the dimple/crack.

[Calvin25]

Thanks guys. $8.55, I'll start over.

Im going to use this die on some scrap and try to learn what happend. Hole size was drilled to #12 per the plans. It was a second pass as the first dimp was a #8.

The Cleavland die is CRISP!

[Kevin Horton]

Originally Posted by Calvin25

Im going to use this die on some scrap and try to learn what happend. Hole size was drilled to #12 per the plans. It was a second pass as the first dimp was a #8.

Practicing on some scrap is a great idea. That'll let you see what works and what doesn't.

I'd try using a #10 drill, and nicely deburring the hole before dimpling. Dimpling it #8, then doing it again with #10 is asking for trouble, in my opinion. I'd do it in one go, with the #10 dimple die.

[9GT]

I always use a small cotton cosmetic pad a lay a thin layer of oil on both sides of the hole I am dimpling, then clean it up with some acetone. Not sure if it does anything but I have never had a crack in any of my larger screw dimples.

[clevtool]

I agree with Kevin. #10 drill and dimple with #10 die right away.

The aluminum will harden slightly after the #8 dimple then the #10 die will essentially flatten the top angle on that hardened dimple back out creating a stressed ring. As for the crack that is likely due to the under size drill. The dimple die has to stretch that material a long way down the funnel.

Thanks for the compliments on the dies!

Mike @ Cleaveland Tool

[aerhed]

The aluminum will harden slightly after the #8 dimple then the #10 die will essentially flatten the top angle on that hardened dimple back out creating a stressed ring. As for the crack that is likely due to the under size drill. The dimple die has to stretch that material a long way down the funnel.

That's right. Every time you bend/deform it gets harder. Also, the slower you deform, the harder it gets. That's why the longest stroke rivet gun you can use is better. Longer stroke=fewer hits= softer shop head=nice barrel shaped shop heads.