Practicing safety wire

My buddy Mike came over to put some work in on his Stewart S-51 Mustang. we mad some good progress and hit a small roadblock. The usual story for a build.

After we wrapped up, Mike showed me the ropes on how to use safety wire.
Step #1

 Step #2

 
 Step #3

 Step #4

Here is my go at it. My very first safety wire job. I still need practice.

And here is Mikes attempt with just using his hands to twist the wires...No Pliers!

Researching dimpling 0.032" thick material for #8 screws

I was floored by yesterdays outcome. Really took the wind out of my sails. I really hate the taste of defeat. It's easy to dwell on the negative I suppose. But...The bright side is that I did not rivet anything yet. So...Not a complete loss.

I called Vans this morning to talk cracked dimples. The conversation was...interesting. The answer is not black and white. Start over, or build on. Vans thinking is this....Its your choice what to do. Replace, or keep going. At the end of the day, what are you comfortable in doing.

One way to look at it is that cracks are not a good thing. But....this area in particular is prone to develop cracks, due to how much pressure the skin is under to form the dimples. So as far as Vans was concerned....Its up to me how to proceed. He did indicate that in his personal observations he hasn't seen a crack propagate out of the screw hole. Not to say it doesn't happen, its just that he hasn't seen it yet.

So...Now. Personally what do I want to do. Well, as much as it sucks... New skins are on order.

The question is how do you avoid cracks. Again...I asked Vans how they felt about the various options that some of the forums discuss. I asked about drilling to #18 or #17, then dimpling. I was surprised that he did not feel this was a wise course of action. His opinion was that opens the door for the dimple and hole to be out of alignment. This could cause the screw to sit improperly in the hole, which in turn can cause issues of their own. He didn't say no, but I could tell if it was him, that's not his choice. He did feel that the #19 hole was the correct course of action. I had also asked him about quality of dies and he did not feel that this was important. As long as the dies are cleveland, avery, plane tools, etc. I should be fine.

He did say that hole preparation is the key. He recommended polishing the hole....Really do my best to alleviate potential stress points before I dimple.

In talking with friends, some mention drilling the hole larger, some don't. One suggestion that seems very logical is to lube the dies to help the skin from being "grabbed" by the die. Mineral oil is suggested. Maybe WD40 will work.

Well...I know this. I have a TON of material to practice on with two botched tank skins. I think mentally I have to be prepared that I may end up with a crack. My goal....is to minimize this as much as possible.

New skins are set to arrive on Wednesday and a #19 reamer will come shortly as well. So I will do every sort of dimpling scenario in efforts to prove to myself how to dimple the thick material and not crack it. When the new skins come...I will dimple first, and then worry about all the match drilling and countersinking that I have to redo.

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. 

Fitted the right wing tank - 4 hours

I work up in the morning and put in another order for cleco's.....Another 325. I'm not going to run out of clecos again. The total count is now 1150 (3/32) clecos plus 50 (3/32) stubby clecos. 

So while at work I came up with the idea that I could screw a 2x4 across the bottom of my wing stand and use that as a means to anchor my straps to. This would ensure that I would not damage the top wing skin as well as give a solid piece to ratchet the tank down.

 
It worked pretty good. I managed to decrease how high the tank wanted to sit proud of the leading edge. It was nearly flush.

Looking around i still could see that the tank skin was not sitting completely tight against the top skin. I could get a fingernail between the skins. The ratcheting action has a tenancy to pull the front, but doesn't want to pull the back as much, hence the gap. I pondered dimpling the skins for the #8 screw attachments now and using them to help align the tank....this is a bit premature in the build stage, and I was concerned that it might trip me up later. I asked the question on Vans Airforce and the suggestion was to go ahead and use #30 celcos in the holes for the #8 screws. I was a tad worried about possibly damaging the threads on the nut plates but that was quickly squashed.
So I began to cleco.



Using both clecos and straps did the trick. I had really nice alignment on the skins and tips as they are now flush. I then match drilled the W-423 joint plate to #30 and cleco'd.

I was now set to drill the baffle to the z-brackets. I started with the inboard end and drilled to #30 with my super long drill bit and cleco'd as I went.

Drilling the inboard end took some thinking. I decided to remove the leading edge assembly, but the W-408 rib is cleco'd to the spar, and there is no way to get to it. So, I simply removed the the W-408 rib and W-423 joint plate from the leading edge assembly and removed the leading edge.



Then, the clecos where accessible so I could remove them. I then removed the W-408 rib and W-423 plate leaving the inboard baffle mounting holes accessible.

Match drilled and cleco'd

Then....I uncleco'd the tank skin and inner ribs from the baffle so I could match drill the baffle to the z-brackets.