Filing the Edges and Corners

Spent about an hour or so tonight filing the edges and the corners of the cutout area of the LE. It was finally warm enough in the garage again to work on the plane. This was basically a repeat of the same effort I used to fabricate the new inspection panel cutout from long ago. The only difference is that the edges are longer and are on a curved surface instead of a straight one. I used the same tools that I used for the access panel job to file down the metal edges of this cutout. I used a standard flat file, a curved rasp, a round rasp, a small jewelers curved file, my small metal ruler to check for edge straightness, and the SafeAir inspection plate that already has the 1/2 inch-radiused corners so that I can use it to test the shape of the corners and adjoining straight edges on either side for a true square fit. Here is the pic of all the tools as I started to file the edges on the top of the LE skin:

I had to once again reposition and re-clamp everything several times so that each edge was supported properly as I started filing. I had to position the edges of the cut section just off the end of the table allow enough clearance for the files moving back and forth, and allow enough room to reposition them as needed. Every time I work with the files I am amazed at how precise you can be with them. The key is to have patience, work slowly, only remove small amounts of material at a time, and CONSTANTLY check your progress against your drawn lines to make sure you are not going to far and removing too much material, which would be devastating at this point. 

I started with the edges and corners on the top side of the LE skin. I worked on those first, so that I could get those shaped properly. Here you can see the "fit" of the inspection plate on the unfinished edges of the LE skin before I started removing material with the files. the edges and the corners all had extra material that needed to be removed. I filed a bit and then kept re-fitting the inspection plate until I was satisfied that both edges were straight, and the 1/2 inch radiused corner was also fitting correctly. Both of the following pics show that there is still some filing to do.

I used the curved rasp to remove the material in each corner by slowly removing the metal and checking the curved line drawn on the skin. The goal was to just meet the sharpee line as well as each edge on either side of the radiused corner, and repeatedly check the fit with the inspection plate until I was satisfied with the fit.

After a few minutes, this side was finally starting to look pretty good:

I have this tendency to try to make everything fit almost perfectly. Some folks would say I have OCD in that regard, but the truth is that I enjoy the craftsmanship part of this project so much that it gives me sense of accomplishment when I am able to form metal with a degree of precision that I used to think could only be accomplished with wood. The reason why it is so important for this to fit together well is that any gaps around the edges will cause the airflow to be disturbed, adding drag to the airplane, and this will just slow me down or rob me of extra performance that could otherwise save me some fuel or allow me to fly faster or to reduce my stall speed considerably. This is where airplane building separates itself from other types of building. If it ain't "perfect," it will most likely deprive you of something, and it may even put your life at risk.

One problem with a "perfect" fit is that I am not allowing much room for primer and paint to be added to the parts later on, so it is very likely that the edges on some of these removable or tight-fitting parts may have to be "reduced" just enough to allow for several mills of that stuff to be applied and still fit together nicely. I'll deal with that later.

Here is the top after most of it has been filed to my satisfaction:

Then I flipped it over and started working on the bottom half. I was able to file the edges out to the tip of the bend so that I would have a good enough reference to match it against line from the other side as much as possible.

Here is a shot of how I would apply the flat file to the edges

Getting closer to completing the bottom corners with the curved rasp

And the last two pics I took of each bottom corner after fitting the access panel to each of them and finally being satisfied with the fit.

I was a little concerned that I may have messed up one of the edges by cutting too close to the edge with the cutoff wheel, but after checking it closely I think everything worked out fine. I used the metal rulers to check the straightness of each of the edges, and even though some optical illusions started messing with my eyes to make me think that the edge was not straight, the ruler sitting flush up against it was proof enough that I should stop filing and walk away before I really messed it up.

SO overall this did not take very long to do - certainly not as long as I though I would, and I am ready for the next step which is to sand all the file marks off of the edges, especially in each of the corners. If I do not manage to remove all the burs and potential stress risers from these edges, they will most certainly start to crack at some point, so proper deburring is an absolute must.  I will sand each corner and each edge until ALL the file marks are gone and the corners are smooth. There are a lot of burs from the Dremel cuts on the inside of the skin, so I will need to make sure that those are removed as well.

So it was a good session tonight with no surprises or issues. Now I'm just working down the remaining list of To-do's I posted previously to get this finished as soon as possible. The part of this that has me nervous is when I fabricate the removable section and start drilling screw holes in that and then start attaching it to the subskin and checking to see f that part will lay completely flush with the rest of the LE skin. Personally I don't think it will for a number of reasons, but I have been pleasantly surprised by my workman before - may be I will again. I sure hope so.