Scratches in sheets while plans building

[FlyingPilot]

So I am plans scratch building a Sonex and saved by going local for material such as 4x12 .032 sheet and angle. I am sorry I did for the sheets. None of the sheets (the 3 required) came with any protective coating on it. Rolled it, put it in the back of the truck and came home. The bottom sheet which was on the outside of the roll has some pretty good scratches on it (some fine, some more noticeable). Was able to rough cut most parts from the top two sheets, but still some fine scratches here and there. I've looked at pictures of other's builder logs and noticed many have scratches on their material while working with it as well. What is the standard on this? When to use the metal, when not to use it? Blue 2 inch painters tape worked well on long cuts with the jigsaw. A lot to be said about the Wiss Model # W14L lightweight hand shears, these things leave a 1/16 ripple on the edge of the cut. Good enough for rough cut outs of parts. I'd like some suggestions on scratches (read somewhere about finger nails catching on a scratch. If it does can it be buffed out. This stuff seems to scratch pretty easily. Any tips on making long cuts on sheets for basic shape channel parts.I see homebuilthelp videos tossing around the aluminum unprotected like nothing. What is the standard, and how fussy do i need to be with it? I'll be primimg and painting the plane. I can't see getting a nice mirrored finish with scratches in it. Please share some of your experiences. Thanks

Thanks,
Rob L

[kevinh]

I used to really freak out about scratches until I saw how effective a hand scotchbright pad was at removing them (and a small amount of other material). The nice thing about the 6061 in the sonex is that it is the same all the way through (as opposed to 2024 alclad where if you scratch through the alclad it you need to at least use primer). I'd say test a piece and see if you can get rid of it with scotchbright and I bet you'll be happy. There is some FAA pub with specific guidance but I don't remember the number right now...

I too am painting and I when I painted my previous aluminum plane, step one was to go at everything with scotchbright anyways...

[Bryan Cotton]

The FAA guidance from 43.13 is you can remove 10% of the thickness. This is in the chapter on corrosion. Still a good guideline for scratches in my opinion. I have seen minor yet ugly scratches buff out with F9 and some determination.

[FlyingPilot]

Thanks for your replies, I will have a look at the guidelines. I don't think the scratches are anywhere close to being down 10% of the thickness. Going to pickup some grades of scotch-brite and give it a try. Btw Kevin, your Waiex photos are great, she's coming along nice. I got most of my .032 parts rough cut, the only .032 part left to cut which has me actually scratching my head on it's layout, is the root/walk wing doubler. Trying to figure out the layout and dimensions for that. Fun Stuff.

Rob

[kmacht]

If you are painting the fix for those minor surface scratches is easy. Not so much if you plant to polish. I scratch built and dealt with cratches by putting a piece of scorch brite in a 1/4 sheet palm sander and going over the parts with it after I finished all my cuts, bends, and holes. A quick wipe down with acetone takes all the aluminum dust off after you finish. The palm sander saved me a lot of hand rubbing. Buy a cheap one though. The scotch Brite will eventually wear away the rubber pad on the sander. I went through three over the course of my build. Harbor freight usually has them on sale for about $10. The other advantage of the scotch Brite method is that the aluminum takes paint really well after.

Keith
#554

[FlyingPilot]

That's a good idea, I do have 2 old junk palm sanders i could use. Which grades (color) scotch-brite do you suggest. I'm picking up some red/maroon tomorrow from Adavanced Auto. I haven't been able to find the other colors, white or gray locally. I tested with green and it is to course. originally wanted a keep weight down with mirrored polished exterior because I might go the corvair route but i don't see it happening with all the extra material handling that happens during a scratch build.

Rob

[wlarson861]

Rob;
I suggest you experiment with a maroon scotch bright on some scrap . put some scratches in it that look like the worst on your skins. You will be surprised how much of the scratch goes away. if you can borrow a little Nuvite F-9 and a buffer from another homebuilder, see how that scratch disappears with a few passes of polish. After getting first hand experience with finishing then you will be in a better position to decide between paint or polish. Also if you get to Oshkosh bring a sample of a badly scratched piece and stop by the Nuvite booth. They can tell you if it can be polished and how much work it may take. They have several methods for restoring deeply corroded and surface damaged metal with some pretty amazing results.

[Bryan Cotton]

Rob,
You are a true Scratch Builder!

[FlyingPilot]

lol Bryan, literally to the sense of the word :). Scratching my head, my material etc. My main reason for this post was the concern for stress risers on the .032 sheet which is mostly used for the airframe's structural strength where required. I've realized that most of the .032 will be under .025 skin with the exception of the fwd fuselage sides. I was able to use some decent looking .032 with minimal scratches for the sides which is good. I might be able to pull off a polished finish after all as long as I get protected .025. I'll work out the scratches from the .032 parts the way you all suggested, prime, assembly and be done. Thanks for all the suggestions! Great site!

Thanks,
Rob