Drilled nutplates on W-423 joint plate. Dimpled #8 screws on tank skin - 3 hours

Using a nutplate jig I drilled the W-423 joint plate for the K1100-08 nutplates. I drew a line down the center of the #19 holes to provide a reference. I then used the jig to drill the holes.


Then, I dimpled them with the #8 screw dies. I was sure to use scotchbrite on the holes to be dimpled. The goal was to smooth out the hole as best as i could to mitigate the risk of cracks. After the hole was dimpled, I went over the hole with scotchbrite again to smooth the hole.

Everything turned out well. So I decided to give the tank skins a shot. I started off with the T-701/W-423 attachment holes. I repeated the process, but low and behold...I have 1 cracked dimple. Crap...
So I carried on. I completed the dimpling the spar attachment holes...About 1 hole in 10 is cracked. Crap! Not sure what to do now.

Test piece for #8 dimples - 1 hour

I've been reading about potential cracking of #8 dimples in the tank skin. I've decided to make a test piece out of material if the same thickness. I've drilled the holes #19 and some #18 to test various methods. I have chose to use my alligator squeezer to dimple the holes. I decided that it is in my best interests for a fast dimple rather than go slow. I want to avoid work hardening the dimple by going slow.

Both the #19 and #18 holes dimpled perfectly. No Sign of cracks, although the #19 holes were a smaller diameter after being dimpled.


I decided that with no signs of cracking on the #19 holes (and a smaller final hole diameter) i'll proceed in that direction.

Finished fabricating T-405 angle. Cut and finished the tank stiffeners - 4 hours

Now that the T-405 angle is roughly cut. I started running it through the sanding station. I clamped the two pieces to get an identical set.

The sanding station makes quick work and it's very easy to shape. Sand, check, sand check. rotate both pieces. Re-clamp Sand the other side, check, sand check. Once I was satisfied...I then moved on to the 3M wheels on the grinder. Then scotchbrite. My hands a black! But the pieces turned out very nice. and I am pleased with the fit on the tank ribs.

Although....I'm not sure how I am going to set those three top rivets and two bottom??? More research needed.
Still in the urge to fabricate. I cut the tank stiffeners. First cut with the band saw. Next was trimming with the aviation snips. Once that was done, I used a file to remove the shear marks on the long edges.

Next was to run each piece through the sanding station, then the fine 3M wheel on the grinder. Its a very slow process....But some good music helps pass the time. I finished up with some scotchbrite on the edges. Not a sharp corner to be found.

Started fabricating the T-405 Angle - 3.5 hours

This is not a job that I was looking forward to. On all of the build logs...I knew this was going to result and a good amount of hours.

Well. First thing first was I drew up a template in AutoCAD according to the dimensions given on the drawings. I printed it full scale and cut it out. Taped it onto the piece and traced the outline.

This give me a good reference point to work to. Using the bad saw, I cut out the pieces.

The next step was to use a file to help work down the edges. This took quite a long time. The work is slow....but its fairly precise.
 
 Next step the T-410 nose plate is used as a guide for the bottom flange of the angle. So, using a dremel, I carefully separated the T-410 and T-407 pieces.

I then marked out lines on the T-410 plate to establish the correct placement on the angle. Once everything was set, I traced a line on both pieces, and cut with a band saw. I checked and re-checked to make sure I made a left, and a right. I did NOT want to mess this one up.

More work with the files....checking, filing, checking some more. Re-traced the 1" radius for reference. More filing.
  

Match drilling and countersinking the left tank - 3 hours

Not much to report. I re-cleco'd the left tank and repeated the exact same process as the right tank. Match drilled the baffle, match drilled the skins. Countersunk the tank skin. Fitted the fuel cap.


 

Not a whole lot to write on as the process is exactly as I wrote yesterday. (Those two outside ribs just suck). I'm not happy with the holes...they've taken a beating. They look works from the outside of the skin, but look good from the inside. They just feel bad when you run your finger along them. I will have to take my time and de-burr them and clean them up.

Counterskinking the right tank skin - fitting and match drilling the left tank - 8 hours

Been doing a ton of reading on the subject. Some folks countersink as per the instructions and some dimple. But there is a division. it's not all one sided. Personally I have chosen to go with the instructions if in doubt. Especially since this is my first build and I am not aware of the pro/cons of each decision.

What I did find from my research is that if you choose to countersink, there is no need to countersink extra deep to allow for a thin layer of proseal between the rivet and the skin (unlike using tank dimple dies for the rib/skin connection) This lead me to a debate on the forums just having the rivet set flush with the skin. Seems that a flush 3/32 rivet will result in a knife edge condition in the slightly thinner 0.032" material. According to the forums this knife edge condition is not wise. I was surprised to read that Vans technical support is not keen on the knife edge condition in this area. The instructions call to machine countersink the rivet, with no red flag on making sure to avoid a knife edge condition.

Oh well....that why there's forums called plans "Gottcha's"   

According to the information in the forums leaving a flush rivet slightly proud will help avoid the knife edge condition. I have chosen to follow this method. The question of the day...is what is the correct dimensions to proceed.

According to the forums and rivet Mil-Spec MIL-R-47196A. The maximum head protrusion for rivet shaving is 0.006"  and a minimum head diameter of 0.161". Therefore if my goal is to countersink to a diameter of 0.162" this will meet the minimum specification for maintaining rivet strength if the rivet is shaved or sanded down flush. Although, my goal will be to leave the rivets proud in this area to maximize strength. Maybe the gap left is a fillet of proseal? That would be ideal!

Here is the countersink diameter on my test piece.

Here is how the rivet sits proud with that diameter. Really minor!



I had posted on Vans Airforce my findings and let it sit for a bit before I took action , just in case someone had chimed in that it was not a good idea. So while I waited I devinyled the left wing skin. 

After an hour I checked back on the post, and all was good. I also double checked with my buddy mike who is an aircraft mechanic and air accident investigator to see what his thoughts were. After consulting with him, I decided that my findings were correct and I completed the riveting on the right wing skin.

The rivet sits slightly proud.

I then removed the baffle and decided to fit up and match drill the fuel cap. I took my time to make sure it was centered and everything looked good. I marked the holes. Clamped it to the skin and re-checked.
 
All was good so I drilled. I'm very happy with how it turned out.

Once that was done, I disassembled the right tank, and cleco'd the left tank. Holy crap those two outside (blank ribs) are awful to get aligned and cleco'd in. I managed to make it work....finally, but the holes are taking a beating. Once the tank was cleco'd I set it on the Left wing and the fit was perfect.



I repeated the same steps as the right tank. Used straps and clecos. Everything fell into place. So I match drilled the joint plate. First to #30 then to #19. I  match drilled the inboard z-bracket.
 
Disassembled the left leading edge to gain access to the outboard leading edge.  
  
 I started to match drill the baffle, but it's getting quite late and I've put in a huge day. So that's it for tonight.

Re-releco'd and match drilled right tank - 3.5 hours

I planned on working a bit longer today than I did. But that's how weekends go. First order of business was to remove the baffle and look at the z- brackets. The holes turned out really good.
(I will remove the primer that is on the z-bracket where proseal makes contact.....its just easier to prime the whole thing at once).

Then I set up the tank skin back in the cradle and clecoed the assembly back together. Oh what a pain. Again, those two outside (blank) ribs are just mean. Once I had everything back together. I started things off by match drilling the baffle/rib holes.

One of the things that I didn't do was drill the joint plate to #19. I did drill them to #30 though. So I re-cleco'd the joint plate back on. Everything was perfect so I match drilled the holes to #19..one by one.

Then I proceeded to match drill all the right tank skin/rib/baffle holes.


Now I am ready to countersink the wing skin. I started to research what the course of action is here, and It's not a simple answer. Time to call it a day.