18-05: Fuel Tank Internal Ribs (#2 - #6)

 Rinse and repeat

From here on, all the fuel tank ribs will be the same, so instead of writing about each one, I will just cover them all in one post (about a month of work probably!). The end rib is the exception - however this will be done the same way as Rib #1.

The Process

Preparation

The success of this process relies upon the preparation before hand. Prior to mixing any sealant, the following is completed (in this order or thereabouts):

• The correct rivets are selected and placed into a glass jar and covered in acetone - first thing when I walk in the shed. 
  
  
  
• White cotton rags are cut into 2-3" squares using a rotary cutter.
  
  
  
• A syringe is selected (or an old one cleaned) and tape is placed on the top of the syringe. 
  
  
  
• A plate, a large tongue depressor and a icy pole stick are placed on the scales. 
  
  
  
• A metal palette knife is ready for the mixing and putting of sealant into the syringe. 
• The compressor is turned on, the pressure set to 25psi and the gun is oiled and tested on the bench to make sure it works.
• A piece of foam is added to the bottom of the bay where I will be riveting, just in case I drop the bucking bar.
• A piece of shop towel paper is placed on the bench to put down any dirty mixing sticks etc (and the bench has been covered in plastic), and a second one for the soaking rivets to dry on. I just use paper towel - no coloured 'chux' etc as the acetone seeps the colour out of these types of cloths.
• Gloves are put on at this point and worn throughout (and the gloves are constantly cleaned or replaced as I go). I keep baby power on the bench next to the gloves box in case I can't get a new glove on. I don't really like wearing 2 pairs. 
• The rib is removed from the skin and all mating surfaces are thoroughly cleaned with acetone, including inside the skin. 

The tank is setup in the cradles, so that I will be able to access each and every rivet. I place a board on the spare end of the cradle as a work surface. 

Here you can see the tank straddling the 2 workhorses, so that I can access each and every rivet easily.

The following tools are laid out: 

• a bucket with yesterday's dirty clecos with cleco pliers
• the black bucket with the 2-3" rag squares
• the deburring tool (for removing excess sealant from the dimples if required)
• an automatic centre punch (for seating rivets properly in the dimples if required)
• a small punch, and a 3/32" punch for aligning any dimples (as required)
• the bucking bar (a small tungsten one)
• a pair of needle nose offset pliers.
• the rivet gun (tested) with the mushroom set
• a small glass jar with clean-up acetone. 
• a LARGE BIN!

Straddling the 2 cradles allows great access to the rivets. I use a lead shot bag inside the tank, right over the timber position, to make sure the tank doesn't tip. 

Sealant Mixing

At this point I am pretty much ready to go. To prepare the sealant I follow this process:

• The acetone from the soaking rivets is poured into the 'clean-up' acetone jar which is on the workhorses next to my tools. The rivets are poured out onto a paper shop towel to dry.
• The scale is turned on and tared to zero with the plate, a tongue depressor and an icypole stick.
• The sealant Part A is removed to the required weight using the tongue depressor, then i use my phone as a calculator to work out how much Part B is needed (10%). The tongue depressor is left on the plate with the sealant that was removed.
  
  
  
• The part B is removed with the icypole stick and placed on the plate (stick too). 
  
  
  
• Once I am at the correct ratio, I wipe all the black off onto the tongue depressor and use this for a rough mixing of the 2 parts. The dirty sticks are placed on the square of paper.
• I start a timer on my phone at this point (roughly mixed)
• Once it is roughly together, the palette knife is used to scrape clean the tongue depressor and properly mix it all together - careful to scrape the plate clean of all the Part A, and look for an even consistent colour. 
• Once mixed, the palette knife is used to wipe it into the syringe.
  
  
   
• I place the plunger in the syringe, and remove the sealant covered tape around the top.
  
   
• I clean the palette knife with a rag and acetone, then throw away the plate, sticks and paper on the bench. 
• I put on new gloves and clean any sealant off the outside of the syringe. 
• The now dry rivets are placed in a plastic bowl next to the tools. Edit: I learned the hard way not to use a plastic bowl - any tiny amount of acetone left melts the bowl, sticks the rivets to it and contaminated the rivets. (headslap). I now use a porcelain bowl from the kitchen (shhhh)

A half-hour in the shop and no rivets are even set yet! 

Finally we are ready to use the sealant. I use the syringe to place a bead along the rib flange, circling each dimple. Where there is a flute, more sealant is applied along the flute to make sure this gap gets filled. I am looking for an even squeeze out along the rib flange. A tongue depressor is then used to smear this into a flat, even thickness film (maybe 1/32 - 1/16" thick). 

The rib is carefully pushed down into the skins, aiming to align the bottom holes first. I then cleco the bottom 4 holes on both sides, then work my way to the top. This method has resulted in almost all the clecos going in first time. 

To actually rivet, I start at the TOP of each rib, and I do 3 rivets in a row on one side, alternating back and forth between the top and the bottom. For every single rivet the following process is followed:

• Clean your fingers and the bucking bar from the last rivet set, using a fresh rag dipped in the acetone jar, then clean the just set rivet shop head a bit to check it is acceptable. 
• Remove the cleco and keep it pulled with the pliers - clean with the same rag. Release the cleco, and clean again. Throw the cleco and pliers in the bucket. 
• Take a look at the dimple and check for excess sealant - a little is fine and not worth cleaning out, but since I haven't used tank dimple dies I don't want too much. If there is a lot, use the rag from above and twist it in the hole using the deburring tool. 
• Use a pair of needle nose offset pliers to pick up a rivet and use these to place it in the hole. This GREATLY reduces the mess from sealant on your fingers, plus putting a rivet in the hole wearing gloves is a challenge.
• Check the rivet is in straight - sometimes the dimples are not completely aligned and this is where the punches are used. I used a combination of the thin and 3/32" punch to align the dimples so the rivet sits flush. I use the automatic punch to make sure it is pushed down hard into the dimple if needed. If it is not in flush before you rivet, it will not become flush during riveting. Sometimes, all it needs is some side pressure on the inside of the rib to push the dimples inline a bit better, and once the rivet is seated properly, it holds the parts aligned. 
• Use the needle end of the pliers to hold the rivet in the hole and wipe the sealant off the shop head of  the rivet on the inside (using the same rag as above). After this, throw away the rag. 
• Grab the gun and centre the mushroom set on the rivet head to hold the rivet in place. 
• Set the rivet. 
• Clean your fingers and the bucking bar from the last rivet...... and just keep going like this!

Occasionally, I need to clean the mushroom set face and/or the skin as a little bit of sealant makes its way around the heads of the rivets onto the skin.

These are the tweezers which have worked well for me

The rivets after setting

Once I have set all the rivets, I do a little clean up around the shop heads and 100% make sure I am happy with what I am seeing with regard to rivet quality. If any are dodgy, now is the time to take them out. 

After this, it is a matter of checking my phone to make sure I am still within the 2 hour window for the sealant remaining in the syringe. In all cases so far, I have been around the 50 mins to 1:15 mark. Clean sealant off the phone!

I then proceed to place a dollop of sealant on each and every shop head, in a swirling motion. If there gets to be too much sealant on the syringe tip, I wipe it on the tape inside the tank. 

After all the shop heads are covered, I do an inspection of any areas where there is not enough squeeze out around the flange and add some additional sealant in those places. 

Finally an icypole stick is used to tool the sealant along the edges of the tape. What I am after is a nice smooth fillet along the rib flange edge, which feathers to zero next to the tape edge. By doing this, the tape can be removed without lifting any of the sealant up along the flange edge. I used a bright torch to visually inspect the entire flange fillet on both sides of the rib for any voids - and add sealant and re-tool if necessary.

This is after tooling and before tape removal.

Finally, the tape is carefully removed and any stray little bits of sealant is cleaned up with acetone. This is the end result:

Here is what the outside skin looks like:

At the end, all tools are wiped clean and the 'dirty' clecos are just left until the next day to be reused again. I have not seen any issues so far with them having any old sealant still attached etc. 

All in all, it takes about 2.5 hours to do one rib and around 40g of sealant using this method. 

So, only 13 more ribs to go!