Scratches in Aluminum ...

Post by **Spike** » Tue Oct 26, 2004 9:57 pm

In reading through the documentation, etc. in the preview plans and the builders sites it seems that aluminum scratches are a worth adversary that a builder must do battle with. But as a new builder I ask to what extent ? Where do you draw the line between a non-perfect surface and a scratch that must be dealt with. Working on some aluminum tonight ( skin stiffners from the training kit) I noticed that the bed of the table sander slightly mars up the surface of the alclad. Yes, you can feel it a bit with your finger nail, but its not like I would really consider it a deep scratch. Its more like the surface finish has been knocked off. Heres an example of a stiffner, and the slight marking on the backside of it :

Stiffner:

And the backside of the stiffner:

So the question is how would you deal with that ? Would you deal with that ? Obviously you could hand sand it with some sand paper.

Since this is not going to be an aircraft part I decided to play with this type of problem a bit and tried to buff out the surface with a scotch brite wheel on the table grinder. The wheel burnished the surface and smoothed it out, though not nearly to the point that the alclad was from the factory. You can barely detect the burnishing with your finger nail, but overall its fairly smooth.

Heres a picture:

So the question is, is using the wheel a valid "fix" for such scratches ? Is this being over paranoid ? What's your opinion ?

-- John

captain_john · Post by **captain_john** » Sun Oct 31, 2004 9:48 pm

Get one of these babies:

They are Scotchbrite wheels on a 3M Roloc arbor. You can buy them at any autobody supply place or Sears. The maroon pads are the most versatile.

They are absolutely MAGICAL!

CJ

Post by **Spike** » Wed Nov 03, 2004 12:44 pm

Captain_John wrote:Get one of these babies:

They are Scotchbrite wheels on a 3M Roloc arbor. You can buy them at any autobody supply place or Sears. The maroon pads are the most versatile.
CJ

Point of clarification, are you saying the arbor or the pads are available at Sears or an autobody supply place ?

-- John

captain_john · Post by **captain_john** » Wed Nov 03, 2004 8:24 pm

Both and all. You can get the kit and kaboodle from Sears if you like.

The autobody store will have the best price though. I use the maroon pads almost exclusively.

CJ

Post by **Spike** » Wed Nov 03, 2004 8:29 pm

Well, you see, I was making an order with Avery today anyway, so I kind of ordered theirs. Im a sucker for convenience

So, the next question is, what are you spinning it with ? It looked like a harbor freight angled die grinder. Is that true ? Thanx for the help

-- John

captain_john · Post by **captain_john** » Wed Nov 03, 2004 9:07 pm

Cool, yah... Avery is great!

I really do not like Harbor Freight. I had a hard time placing the order and totally lost confidence in them as a company. I told them I can buy cheap tools anywhere and not to send me anymore catalogs.

That said, yes, it is an angle grinder. $30 or less is a great price. I have seen them for $50 - $60 as well. Mine is an Ingersoll Rand I picked up at Lowes for $30.

Any way you slice it, It is my most used tool!

CJ

Post by **Spike** » Wed Nov 03, 2004 9:36 pm

I can understand. My rule of thumb concerning Harbor Freight is to only by inanimate objects there. They are great for things like bench vices, clamps, and such, but I dont buy anything that takes electricity or air power.

-- John

Akroguy · Post by **Akroguy** » Mon Nov 08, 2004 5:15 pm

For inside the airplane, shoot it with some primer. The scratches on the bottom of the stiffeners are going to be mated to the skins. It's generally considered good practice to prime mating surfaces to reduce the chance for galvanic reaction to electrolyte (water). For outside, don't sweat it if you're going to paint the airplane. You WILL rash your airplane parts during the years it takes to build one of these. For all but nasty scrapes and gouges that kick up a burr of aluminum cladding, polish it out with the scotchbrite wheel or die grinder pads, shoot it with primer if you want, and JUST BUILD THE PLANE. (Typical response from Van's tech support. Why? BECAUSE THEY'RE RIGHT!)

So there.

Brian

Post by **Spike** » Wed Nov 10, 2004 10:30 am

Thanx for the recommendation of getting scotch brite pads and the ROLOC arbor. I received mine last night from Avery, chucked it up in a die grinder and took it for a small test drive. What a great combination. This will be perfect for taking scratches out of flat surfaces such as skins. Kudos to you

-- John

728GD · Post by **728GD** » Wed Nov 10, 2004 11:24 am

Spike - Look at a 6-in scotchbrite wheel and mount it on your drill press. These are great for deburring edges and makeing smooth round corners. The smaller 3-inch you have now will get into the small places, but you can really put some effort into the 6-inch on a drill press. Avery will also have the parts.

Post by **Spike** » Wed Nov 10, 2004 11:25 am

Ill put that in my back pocket. I need to slow down with Avery though if you know what I mean

Post by **Spike** » Sat Dec 18, 2004 11:43 am

Captain_John wrote:Get one of these babies:

They are Scotchbrite wheels on a 3M Roloc arbor. You can buy them at any autobody supply place or Sears. The maroon pads are the most versatile.

They are absolutely MAGICAL!

CJ

Well, its been a few months John and you dont know how much I want to kiss you for that bit of advice. Prepping parts with this thing is awesome. They have saved so much time on the HS spar doublers it isnt funny. I will disagree with you though on the maroon pads. I think the blueish green pads are the best. The maroon pads eat up the material too fast for my taste. Boy has this tool made life so much better.

-- John

captain_john · Post by **captain_john** » Sat Dec 18, 2004 12:03 pm

Hahaha, I will be sure to stand at arms length when you come up for a visit!

I am glad you like the rolocs!

CJ

guycole · Post by **guycole** » Thu May 19, 2005 12:00 am

I am finishing up my HS and I also see scratch marks on the skins where my rib tips made it through the vinyl. I'm not sure how deep these are.

I read all the comments, I'll try the various flavors of scotch brite. Thanks for the tip.

My question is what happens after the scotch brite? The Vans assembly book says (end of 5b) "Any area that has been sanded for scratch removal must be primed."

Does this mean I must now prime the entire skin or can I simply spray on some self etching primer over the sanded area and move on?

Post by **Spike** » Thu May 19, 2005 7:37 am

just spray some primer over the area. Alternatively, you could wait until you paint the plane if you are comfortable with the amount of time that may be and the moisture content of the air.

-- Spike

Does this mean I must now prime the entire skin or can I simply spray on some self etching primer over the sanded area and move on?

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