LE Prep Episode 3

Edit 6-9-17 - I revised some of this post to make it more readable, and also to correct a gross oversight on my part.  I previously used the term "kerf" to describe the process of applying a small bend in the edge of each skin so that it provides some spring back when riveted in place to prevent the edge from curling upward and creating a gap between the two surfaces. This was not the correct term to use, as kerfing is an entirely different procedure for a different reason.

The other problem with this is that in previous posts from long ago when working on my rudder I may have also referred to this process as "rollling" the leading edge, which is also an entirely different procedure for a different purpose. The problem is with the way the edge forming tools is contructed. It is basically a set of modified locking pliers with a set of custom-positioned rollers welded on to the ends of the pliers at a pre-determined angle. The "rollers" on this edge forming tool can be confused with the term "edge rolling," and thus the confusion.

SO let me stand corrected - the official name of the tool that I am about to use is an EDGE FORMING TOOL. It uses a set of rollers to force a small bend in the edge of the skin. This process has NOTHING to do with kerfing, which is a procedure that awaits me whenever I get back to working on the main wing skins. There, now I feel better..... ----------End edit.

No pics tonight. One other thing I almost forgot about was the outer edges of the LE skin. So I went out last night and ran my finger across the edges, and it took less than a second for me to discover the same small bumps about 3 inches apart from each other along the edges. These are the separation points where the skin is still attached to the metal blank that is placed into the CNC machine to perform the initial cutout of the LE skin. Vans does not remove these seemingly minor bumps from the skins. They can, however, act as stress concentration points, and could cause metal fatigue and cracking if they are not smoothed out.

So, like everything else with this kit, all these little bumps along the edge need to be filed and smoothed. I used my flat jewelers file and a piece of 320 aluminum oxide sand paper glued to a 1/2 inch wood dowel to file and smooth all of the bumps. I also had to residual scratches that needed a bit more work to smooth those out before priming everything.

A call to Vans also revealed two more things. I need to slightly round the corners to get rid of the sharp corners - another potential stress concentration point on the skin. They also confirmed that I will want to slightly bend the edges of the LE skin where they attach to the wing spar flange. So now I have to find my edge bending tool, practice with it on some scrap metal, and hope like heck that I don't screw up the edges on the LE skin. I think I will need to clear off a large area on my work bench so I can clamp down each skin edge so I can use both hands to draw the edge bending tool along the skin edges.

As I recall, one problem many builders were having with applying this small bend to the edge of the skin was that they were using the tool incorrectly. They close the pliers too tightly so it is extremely hard to run the rollers across the skin to achieve the small bend. Then, when they start to apply the bend the rollers slip off the edge, messing up the edge of the skin along the way. Only slight pressure is needed on the skin while the tool is drawn toward you to create a very small and barely noticeable bend on the edge of the skin.Cleaveland Tools now has a video on their website that demonstrates how to set this tool up and use it properly.

Tomorrow I will probably scuff and clean the subskin, apply the bend to the edges, and on Thursday I should be ready to prime a bunch of metal again. Then more assembly, measuring, disassembly, cutting, deburring, etc., etc.

And to think I was going to have my fuel tanks done by the end of this summer - yeah right!

KPR.