The folly(?) of scratch removal
Will these factory-installed scratches kill you?
I don't know, maybe I'm an idiot, but the front of the manual talks at great length about how scratches in aluminum can lead to cracks, and cracks in the wing ribs sound like the sort of thing that could really ruin your day. It is hard to instill, they say, "the importance of proper finishing technique" in novice builders. And so I start sanding and grinding, taking those words to heart.
To: support@vansaircraft.com From: Paul Hi guys, I'm getting frustrated. All of the ribs in my kit so far (RV-9 HS and wing ribs) have come from the factory with lots of nicks on the inside webs and flanges. I don't know if they are happening during manufacturing or shipping (nesting the ribs together seems to cause some of them), but they are pretty deep and removing them is a pain. They are deep enough to feel easily with a fingernail, and most come out with some scrubbing with 330 grit. Some are deeper and require more drastic measures. The inside flanges are the worst since I can't get any sort of power tool on them. My question to you is this. The manual says to "remove all scratches, no matter how deep", but no builder I know actually does this. Some say to remove anything you can feel with your fingernail and that is what I have been doing ... to the tune of 6 hours for one wing's worth of ribs. Others only smooth out the deepest gashes. If the ribs came "clean" from the factory I can understand your position, but when I receive parts with so much apparent damage I've got to wonder what you really mean by scratch removal.
From: "Scott Risan " (scottr@vansaircraft.com) To: Paul Paul, unless the scratch is really deep, light sanding to remove any 'high' material is sufficient. "High' being any material that is above the flat rib material....normally takes very little work. No need to remove the scratch completely. If it's really deep....say 20- 30% of the material thickness, then consider a replacement part. van'sWell, that's nice, but I may keep on removing scratches anyway. Several A&Ps (online) and other builders (in person) have advised me to keep sanding. I wish Van's would just improve their production and/or shipping of these parts so I don't have to worry.
just prior to this in the manual, it says that the solution to knowing if a scratch is deep enough to be concerned about is to simply remove ALL scratches. In the real world, this is not very practical as there will be light scratches on most surfaces of the plane by the time you're done and ready to paint. It is a bit of a gray area but common sense can be used in most cases...is the scratch on an edge or a corner?....if so, spend a bit more time cleaning that one up. If there is a question as to whether its too deep to use the part, call us or send us a photo and we'll help out. Van's