Round 2 - Making a new removeable section and Fitting it to the LE

Weather and holidays kept me from getting much done on the plane. Finally got some warmer weather and started to work on another removeable section to see if I could get it to fit better. To recap a bit, I had use a file folder template and a very inaccurate and un-scientific approach to use a drill bit to pre-mark the #30 hole locations from the subskin, so that I could then transfer those holes from the template to the metal. So basically this approach was designed to create a template with pre-marked hole locations that SHOULD line up correctly with the cutout section of the LE.

Unfortunately after bending the part around the LE and securing it with clecoes, there were some gaps along the bottom section that I was just not too satisfied with, and I also mis-marked one of the hole locations. So I knew I was going to need to make another one and try again.

Here is pick of the old paper template the first attempt at making the removeable section after removing it from the LE. The amount of spring back on the metal was really amazing to see. The part barely has any kind of permanent bend in it after I wrapped it around the top an bottom of the LE. nd left it clecoed that way for several days.

The first thing I decided to do was to use the existing paper template and part to draw out dimensions on my .025 metal sheet and make the edges slightly larger than before to ensure that all the gaps would be taken care of. I drew another border, using one of the factory edges of the metal to ensure that one side was truly straight. The other 3 edges were not from the factory cut, and so I had to ensure that these 3 sides would confirm to the cutout section and would not leave unwanted gaps. I think I added about 1/16th of an inch more material than previously, and I knew that this would most likely mean that I would need to spend a lot more time trimming the edges down to their final sizes to get everything to fit.

Here is the second piece of metal without any holes added:

I felt that the reason for the gaps was because the drilled holes were just off the mark enough to cause the edges to separate from the LE skins a little too much - so how to solve that problem?

I decided that for this second attempt I did not want to predrill the holes using the same paper template approach as last time, and instead I id some research, and ended up ordering anew tool that I had never used before - a #30 strap duplicator show below:

This is a rather interesting tool to say the least, and I ended up having some really good and some not so god experiences with it. The purpose of this tool to provide a way for you locate a hole of an overlapping or top side piece of metal (my fabricated part) that sits on top of another piece of metal underneath (my subskin #30 screw hole) that already has a hole in it that you are trying to match with the part on top. The bent end on the right is tapered to allows you to insert it between two pieces of metal to pry up the top piece if necessary, just enough to allow you to then insert the #30 pin on the other side into the hole in the bottom piece of metal. The top part of the tool then rests on the top piece of metal. The top flange has hardened steel knob on it with a #30 hole. The top part of the bottom flange of the tool, directly above the pin, is also hardened, and has a small recess where your drill bit ends up after you drill the matching hole through the top skin. IOW, the drill bit goes through the hole in the knob on the top, and drill the hole in the top skin, but is not allowed to continue drilling all the way through the bottom skin. This ensures that the hole that is already drilled on the bottom skin is left untouched by the drill bit. The end result is that you are able to drill a hole in a top skin that perfectly lines up with a hole in a bottom skin without ever being able to see the hole on the covered up bottom skin.

Before I could use this tool to drill the matching screw holes, I needed to work on the short edges of the metal that rest on the rear edges of the top and bottom part of the cutout in the LE. I started with the bottom rear edge first, and made sure that the factory edge on one of the long sides was truly straight and butted up against the LE skin.  I would trial fit the straight edge to the bottom side of the LE cutout, remove the part, use my scotch brite wheel to remove some material, and then repeat the process. All I kept thinking at this point was how much I truly appreciate the precision of tools like laser cutters and CNC computer driven cutting and punching machines. Unfortunately I did not have any of that, so this part fabrication exercise was going to be truly freehand.

Amazingly I was able to get  a pretty patch of both radiused corners and the three sides along the bottom half of the LE cutout. Once I knew that the edges were fitting the way that I wanted them to, the next step was to start locating and drilling the screw holes by using the strap duplicator tool. the one MAJOR problem was - with no holes already drilled in the part, how was I going to secure it to allow me to use the tool and the drill to drill the necessary holes. 

The answer: GORILLA TAPE!!!

I decided to use DUCT tape to position and hold the metal in place  so that I could then start using the strap duplicator tool and hold it in position with my left hand while holding the drill in my right hand. I have to say that this process worked out very well, but it was rather involved process that I had to kind of figure out as I went. The first challenge was how to drill the first hole. Critical to that process was deciding exactly where to place the duct tape so that it left enough flexibility to allow me to slip the tool into position and then be able to re-secure everything in pace to make sure that the hole was drilled in precisely the right spot. Here is a shot of the part taped about half way up the bottom of the LE, with the pin of the tool already inserted into the hole in the bottom skin, and the top of the tool in position over the top skin - ready to drill the first hole.

This was most nervous moment for me, because I knew that only the duct tape was the ONLY thing keeping the top skin of the part from moving. The tool does not secure the top skin at all, until you apply pressure on it like you would a pair of tweezers, which is basically what this tool is, which then helps hold the top skin in position while you drill the hole. One thing I realized very quickly, even with everything locked down as much as possible, is that the thickness f the tool itself is going to force the top sin to bend upward slightly, away from the bottom skin. I was concerned that this might cause the top hole to become slightly misaligned with the bottom hole. However, after I drilled the first hole I was very pleasantly surprised to see the top and bottom holes seem to line up almost perfectly. Here is the pin inserted into the bottom skin under the top skin shown above, which effectively locates the position where the hole in the top skin needs to be:

And here is the drill bit inserted into the pilot on the top part of the tool. It only took a second or two to drill the hole in the top skin. As I said earlier, the drill bit hits the top part of the bottom flange of the tool and does not penetrate the bottom hole at all. SO my first experience using the tool was quite pleasant.

This next pic is a little bright, but it shows the freshly hole in the top skin aligning perfectly with the hole in the bottom skin. Mission accomplished.. One down, 19 more to go. I purposely decided to drill the bottom rear edge holes first, because I needed these in pace to serve as anchors to hold the bottom edge in place while I continued to drill the other holes along both edges.

After this first hole was drilled,  developed a process where I would insert a cleco in the new hole, and then repositioned the tool for the next hole. IN this case I decided to drill the other corner hole instead of moving in a line from left to right. This way I could secure both corners to prevent the part from slipping out of position as the skin was raised to insert the tool into the next hole. This kept the side edges and the rear edge of the part in place exactly where I wanted it as I drilled each new hole along that edge.

Here is the second new hole on the other side of the rear edge of the part:

And continuing on, here the two corner holes are now clecoed, and I am finishing up the two remaining holes along that edge. This was done very quickly and worked great. Yo can also see that the edges of the part are almost perfectly aligned with the edges of the LE skin:

I did have to keep removing other surrounding clecoes to make room for the long handle of the tool. It was just another very common repetitive exercise in airplane building of clecoe removal, tool insertion, clecoe replacement, drill the hole, wash, rinse, and repeat. I'll finish the rest of this up tomorrow, as the side edge holes a presented a bit more of challenge and required some slightly different procedures to complete them all. Then there were some problems with the tool that I will discuss as well.