Rudder deburring and priming

Over the last two weeks I’ve spent about 13 hours working on the plane. It was mostly tedious work since I had to final drill all of the holes in the rudder skins and skeleton, and then I had to debur all of those holes. Deburring is the least exciting task I’ve had to do while building the rudder so far but it is important so I’ll continue to do it.

I actually had a couple things happen that gave me some stress over the last week so here they are:

First, I had some trouble deburring holes.  You want to debur the holes because the burs leftover from drilling can potentially prevent the parts from fitting together properly when it comes time to rivet (or prevent the rivet from fitting properly) and can create places where stress can concentrate which could lead to cracks in the metal. I have a couple different tools that I use to debur the holes but they both work the same way. Basically you stick them into the top of the hole and spin them once, or twice and they are supposed to remove all of the burs.  They way I am using them (I’m assuming it’s user error), neither one of them seem to completely remove the bur around the edges of the holes without risking removing too much material away from the holes. Almost every time I use either of them, I can still catch my finger nail on a bur around the edge. This leads to using the tools a little more, and then a little more, and before you know it you are starting to countersink the hole rather than debur it and that’s something you really want to avoid. If the aluminum is really thin, like the skins are, then you risk enlarging the rivet hole and that’s not good either.

Since I didn’t want to risk ruining the rudder skins I did one or two rotations with the deburring tool and left it at that. There were still burs that I could feel but I didn’t want to risk it so I went ahead and dimpled the skins anyway. This lead to even worse burs on the bottom of the dimple. I worried about this for a day or so and then tried to clean up the dimples by running a file along them which may have worked well if I was more patient but I was worried about taking away aluminum that wasn’t a bur. Then I tried sandpaper and that worked pretty well. Finally I tried a maroon scotchbrite pad. This actually worked really well! Since I plan to prime all of the parts, and scuffing them with a scotchbrite pad is part of the prep process for priming, I decided to just leave them alone and make sure I went over all of the holes really well with the pad before I primed them. This created nice smooth dimples and I feel a lot better about them now. I think I may start to use a scochbrite pad to do most of the hole deburring from now on. I just need to figure out if I should clean the aluminum before I use the pad because I seem to remembera post on the Van’s Airforce forums that mentioned that you could be embedding oils and dirt in the aluminum if you don’t clean it before you scuff it and maybe I’m just overthinking this and shouldn’t worry about it so much. I tend to do that.

The other big mistake I made was when I was putting the edge break in the rudder skins. It’s a very slight bend you put in the metal at the trailing edge so that the skin will lay flat against the other piece that it will be riveted to. Well I have this edge forming tool that does just that. It’s basically vice grip pliers with some rollers on the end that have a slight bend in the top one. You put it on the edge and pull towards you and you’re done. Unless you’re me. Then you screw it up even after you’ve practiced on some scrap parts. The thing is, while you pull it towards you, you’re supposed to push it towards the skin at the same time so that it doesn’t roll off the edge. Well I’m apparently too strong for my own good because I pushed it right up onto the skin, past the flange on the roller that’s supposed to keep you from doing just that. This put a much larger bend in the skin than should have been there. Now a proper edge break is almost imperceptible unless you are looking at the right angle or have a light reflecting off of it, but here’s what I ended up with:

img_20170121_114540

And to add insult to injury, I did the exact same thing a little farther along on the skin. I did the best I could do to bend it back and smooth out the skin but there was only so much I was able to do. Here is the worst section of it:

IMG_20170123_060737.jpg

I haven’t decided yet if I’m going to replace it. I keep thinking well it’s probably just a cosmetic issue and I may be the only one who notices it so it’s not worth it. It’s a $45 part and will put me back a week or two while I wait for it to arrive, not to mention the work I will have to redo. But then I worry that it will affect the feel of the airplane (the plans do mention how important a straight trailing edge is after all), and heck $45 isn’t that much to fix a cosmetic issue since I just started building. To help me decide I went ahead and started a post on the forums asking if it will be more than a cosmetic issue and if there is anything I can do to clean the edge up.

I also got a bunch of priming done. I did everything except for the skin with the bad edge since I may end up replacing it, and I’m waiting on a new stiffener for that side that I will have to match drill anyway. It got countersunk while it was being deburred. I plan to add a post or a page sometime that will go more in depth in my decision to prime and what I am using but for now I am using Stewart Systems EkoPoxy. It’s water based, non-toxic, and easy to clean up. The problem is that it takes several days to fully cure so I’m not going to start riveting the rudder until it has had some time to harden.

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