The first step was to nibble away the flange on the end plates between the Cleco tabs. My first plan was to nibble with the outside of the flange up so I could easily see what I was doing. The nibbler would stop against the plate to control how much of the flange was left for welding.
I cut little notches and then cleaned them up. The Clecos act as stops to assure I don't cut off the tabs.
It worked fine and left just the amount of flange I wanted for welding, just to the edge of the radius. The idea is to make an easy fusion weld and the penetration behind the weld would fill the corner making it easy to clean up any flux inside the tank to prevent future corrosion. A corner weld should also make the bending loads on the weld joint less than at the end of the 1/2" flange.
The problem I found was that the chips come out the bottom of the nibbler and scratched the end plate as it rubbed against the nibbler, bad plan.
I made a new end plate in about 45 minutes. I'm getting too good at this.
I'll nibble this with the outside of the flange down this time so the chips are free to fall. I also put strips of Gorilla tape along the radius to protect it and to control the depth of the nibble.
Again the Clecos act as stops for the tabs.
It was a little more awkward to do this but it worked. I first did the perpendicular cuts as I did previously. It worked but it was slow. I have a lot of notches on the flanges and then on the skin.
Next I tried cutting notches at each end and then driving the nibbler along the plate. I couldn't make it work well.
Next I tried the same end cuts and then just a sideways motion using the back of the nibbler as a guide along the edge of the aluminum. It took 3 passes and it was done, and they went quick.
It did take some practice to hold the edge touching the nibbler housing to make a nice straight cut.
In the end this was how I did the remaining cuts.
Once the notches were cut I cleaned up the corners around the Clecos to reduce the chances of cutting myself on a sharp corner. It did work, I never cut myself.
The edges and tabs came out well.
I then assembled the end plates on the skin and used the end plate as a stop for the skin notches. It was much more awkward to do this with the whole tank in hand but it worked. It doesn't cut as deep because the cut edge of the end plate hits the housing of the nibbler. It's a small difference, about 0.020", and my experiments say it should not cause a problem welding.
Again I cleaned up the tabs on the skin just like the end plates.
The top seam was done the same way and everything is Clecoed back together ready to tack weld. So far the plan is working.
There are 2 or 3 tack weld between every tab. I found that a tack every 1/2" - 3/4" was needed or the skin will pucker out creating a slight gap when the torch heats it. Oh yeah, I'm Oxy-Acetylene welding the tank.
Some of the things I've learned Oxy-Acetylene welding 0.040" Aluminum are:
- You only need to flux the edges of the assembled parts to weld,
- It's easier to weld aluminum that is fit very tight, the aluminum is thin and gaps lead to holes, even more so when you are trying to fusion weld a corner,
- You can almost gas weld steel in the dark because it makes so much light, You need bright light at the weld for Aluminum,
- Use the biggest tip you can control, you want to minimize the size of the heat affected zone to prevent holes forming, if the metal doesn't quickly puddle you are using to small a tip,
- The rod can be used as a heat sink and to stir metal to get it to flow together,
- With these 2 pieces of sheet aluminum at 90 degrees to each other start the torch at the outer edge, flame parallel to the outer skin, it will take more heat to get the outer skin to flow than the piece which is perpendicular to the flame, which will easily heat enough to make a hole,
- If a gap opens either stop and hammer it shut, or quickly get the rod into the puddle to cool it while you use the rod to run the bead in the area of the gap, then you can go back to doing the fusion weld.
- If a hole opens get out of there and let it cool, work your fill puddle in steps around the edges,
- If the weld is not smooth and well bonded it might be strong enough but it will leak.
The tabs were easily cut off with the snips leaving a nice tight spot for a tack weld.
A nice looking section of welding.
While washing and scrubbing the inside of the tank to get rid of the flux I found a few leaks where the water sprayed through. Those were a quick fix.
I then used Gorilla tape to seal the access panel. I also had some tape on the inside which the air pressure blew down tight. I found before that the blower end of my vacuum will only put out 2 psi so it's a quick way to pressurize the tank. Put a pressure gauge, or water manometer, on the outlet of the tank and use a dimmer control on the vacuum to slowly bring it up to pressure.
Bubble solution quickly finds small leaks. I still plan to pressurize the tank and let it set to see if there are any leaks so small I missed them with the bubbles. You can't do that with the vacuum blowing.
With the leaks fixed the tank was treated with Alodine to give a little better corrosion protection and the access panel was screwed on.
I applied sealant around the screws and with 2 beads between them.
I started the assembly with 4 screws in position through the clamp ring and carefully started them before starting all the others. I didn't want the sealant smeared, just compressed to make a good seal. Once all the screws were started I put some more sealant under the edge of the tank opening. With the screws tightened I used the round end of a craft stick to clean up the sealant.
The front and back of the finished tank. The weld on the forward seam is the best and it's the one I did first. I had a lot of gaps open on the aft seam. I eventually figured out that if I kept the rod close and in motion, even though I didn't use it in the fusion weld, I could more quickly get it into the puddle at the start of a gap, if it formed, and keep on welding. The gaps this worked for were only about 0.010". When the gap opened you suddenly had a small puddle going on the edge of each piece but not enough metal to bridge the gap without getting the rod quickly in the puddle. Any hesitation and the skin, being perpendicular to the flame, would form a hole.
The square bottom and tapered top of the tank can be seen here.
The outlet fitting turned out to be easy to weld. The small welding lip on it fused easily with the flange on the tank.
In the fuselage setting on the supports. I need to make the straps which will hold it in place.
There are some bolts in the front which limit how far forward the tank can go as well as the forward struts of the Cabanes.
The straight edge shows the cowling line. It looks like the filler will be out of the cowling. I may need a slight bump in the cowl. Once the tank is strapped in place I can put the filler neck hole in the cowling and work out any bump needed.
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