Counter Sink or Dimple

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Counter Sink or Dimple

Postby BucF16 » Sun Mar 06, 2016 4:17 pm

Quick Question; The manual calls to countersink the rivet holes on the trailing edge metal (both wing and Flap/aileron). I have always heard that one should dimple in AL with thickness less than .041. I tried to counter sink a sample, and to get the correct amount of "sink", the hole became irregular. Any thoughts?

Thanks,
Bruce
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Re: Counter Sink or Dimple

Postby SheepdogRD » Sun Mar 06, 2016 4:59 pm

I drilled the holes, disassembled, dimpled the trailing edge material and countersunk the capstrip. That produced a flush surface without removing metal.

I also used a rivet washer on the capstrip side to prevent pull-through.
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Re: Counter Sink or Dimple

Postby BucF16 » Mon Mar 07, 2016 8:54 am

SheepDog, Thank You for the quick response! Your method is as I intended to approach this issue. This makes me feel better about my intuition going forward. It's been a few years since I've been engaged in a project.

Cheers,
Bruce

Hey BlueMax, Get to Work :mrgreen:
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Re: Counter Sink or Dimple

Postby danerazz » Tue Mar 08, 2016 8:11 am

You countersink material that is as thick or thicker than the rivet head height, you dimple material that is thinner than the rivet head.

The main thing is if you were to countersink, it should not make the hole larger than what you drilled.
Dane

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Re: Counter Sink or Dimple

Postby CanadianSheepHunter » Wed Nov 06, 2019 6:38 pm

BucF16 wrote:Quick Question; The manual calls to countersink the rivet holes on the trailing edge metal (both wing and Flap/aileron). I have always heard that one should dimple in AL with thickness less than .041. I tried to counter sink a sample, and to get the correct amount of "sink", the hole became irregular. Any thoughts?

Thanks,
Bruce


Would this apply to a Superstol trailing edge metal(wing/flap/aileron)?...I don't recall reading about it in the Superstol build manual, and I'm pretty sure you guys are referring to the Hylander

thx
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Re: Counter Sink or Dimple

Postby danerazz » Wed Nov 06, 2019 8:54 pm

The techniques are for any application: countersink material that is as thick or thicker than the rivet head height and dimple anything thinner. If it is dimpled, the mating surface also has to be dimpled or countersunk appropriately, and obviously that countersink/dimple would have to be larger/deeper to accommodate the material thickness of the dimple.
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Re: Counter Sink or Dimple

Postby danerazz » Wed Nov 06, 2019 9:00 pm

Also, I know the original question is quite old, but countersinks that leave a jagged hole are usually due to poor seating of the tool holder on the face of the material or not using a piloted countersink (ALWAYS use a piloted countersink in a microstop holder). If the countersink is allowed to shift at all (laterally or not perpendicular) in relation to the workpiece it will auger out the hole, even with a piloted countersink. This is worse if the material is right at the minimum thickness for the required depth.
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Re: Counter Sink or Dimple

Postby gkremers » Thu Nov 07, 2019 1:01 pm

Just a follow up to what Dane mentioned.
It is also a big help if you use a drill guide on the backside of the material being countersunk. I had all different shapes and sizes made out of scrap material with #27, #30 and #40 holes as guides. It keeps the countersink centered and does not let it chatter.

Gary
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Re: Counter Sink or Dimple

Postby Tralika » Thu Nov 07, 2019 1:12 pm

The EAA website Hints for Homebuilders has several videos on both countersinking and dimpling that might be helpful.
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Re: Counter Sink or Dimple

Postby BucF16 » Thu Nov 07, 2019 7:37 pm

Yep this thread is old, and I used this forum, and EAA "Help for Homebuilders" videos for guidance.

Good Luck,
Cheers,
Bruce
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Re: Counter Sink or Dimple

Postby CanadianSheepHunter » Thu Nov 21, 2019 8:27 pm

CanadianSheepHunter wrote:
BucF16 wrote:Quick Question; The manual calls to countersink the rivet holes on the trailing edge metal (both wing and Flap/aileron). I have always heard that one should dimple in AL with thickness less than .041. I tried to counter sink a sample, and to get the correct amount of "sink", the hole became irregular. Any thoughts?

Thanks,
Bruce


Would this apply to a Superstol trailing edge metal(wing/flap/aileron)?...I don't recall reading about it in the Superstol build manual, and I'm pretty sure you guys are referring to the Hylander

thx


I called the factory today to ask if this applied at all to a Superstol they said no. I asked why is it only required on the Hylander they said "thats the way it was engineered".
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Re: Counter Sink or Dimple

Postby AV8R Paul » Mon Nov 25, 2019 11:36 am

I will concur, the Hole that you are drilling at the bottom of the C’Sink should remain the fulldimeter of the starter hole. If you run the C’Sink too deep, the hole diameter will get larger. If it does get larger it means the skin sheet metal is getting too thin to support the load, and will allow the flat head rivet to pull out. On the old Kitfox SLSA I owned, the the trailing edge of the Flaperon was both Bonded with a bead of Loctite Hysol & riveted ever 8 or so inches. When I purchased the plane, in doing the pre-buy inspection I noticed one rivet had been drilled too deep, the head of the flat head screw was .015 to .020 below the surface of the skin. I only found one that was below the surface significantly.

I was flying out for a Kitfox fly-in and landed in Lubbock, Texas spent the night. The next morning I got up to fly and as I did the walk around, I found the rivet in question had pulled through and the two adjacent rivets to either side of the rivet had also pulled completely out, they were both good rivets. I am really glad I caught it on the pre-flight, if I had missed it it could have unzipped the rivets even further due to the flight loads on the Flaperons. I did a field repair, I went to Lowe’s and bought some 1 inch wide velcro straps and wrapped them around the flatiron, spacing them 45 or so inches apart to hold the flatiron skins together), and flew home to repair the Flaperon. When I got home I found that the velcro did an EXCELLENT job of holding the Flaperon together. I also found that two of the ribs (1/4 inch Foam Ribs) had torn apart, and the trailing edge had come unglued and about 28 inches of the trailing edge had split open and a 4th rivet was ready to tear thru. It could have caused a fatal accident. Without a doubt the Head of a flat head shouldn’t be as close to flush as possible and not more than about .005 recessed from the surface of the skin.

Paul Z

danerazz wrote:You countersink material that is as thick or thicker than the rivet head height, you dimple material that is thinner than the rivet head.

The main thing is if you were to countersink, it should not make the hole larger than what you drilled.
AV8R Paul
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