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Removing material thickness 16-02 Step 6

I'm working on Section 16 - Top Wing Skins and step 6 says to remove material at the joint of W-00002 & W-00003. Before I start grinding away, does anyone have suggestions on how I should proceed?
 
Option 1 - This process that has worked for me;
-Mark the top surface of each skin "NOT THIS SIDE!". You want to sand the under side of the skins.
-Glue sand paper to a flat piece of wood (preferably 3/4" or thicker). Make a couple sanding blocks.
-Secure skin to workbench so the area you plan to sand down is on a corner of the bench.
-Protect the area you will not be sanding with a diagonal strip of tape.
-Use some pieces of aluminum the same thickness as the skin for spacers (.032 for the inboard skin, .025 for outboard skins most RV models), if for example the taper area is 1" x 1", clamp the spacer sheet 1.5" x 1.5" diagonally from the corner.
-The idea is to sand both the spacer piece and skin in the same motion. This establishes the taper angle. Light even pressure.
-Don't take too much material out, ideally about 1/2 normal thickness along the edges, avoid sanding down to a knife edge.
Of course all this happens before you dimple these skins & should be noted that care most be applied when finally dimpling these thin portions.

Option 2 -
-mark & protect skin as above
-use a big flat file & SLOWLY work towards desired taper
-finish off with fine grit sand paper block
Not as much control with this process but what ever works for you.
 
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After researching this site, I used a 2-inch Roloc pad with good results. Agree you should tape off the area to be worked but disagree about removing material from the underside of each skin (16-02 says to remove material from the top of the inboard skin and the bottom of the outboard).

This definitely is something to try first on some scrap material but isn't that hard once you practice a bit and if you take your time.
 
Scarf joint

RV7 has a similar scarf joint. I did as mentioned. I used shims to keep from cutting too much. I actually used a Vixen file to get close then various grits of sand paper on blocks to finish. Top of one skin, bottom of the other.
 
Your suggestions all sound good but I'm not sure about sanding the bottoms of both skins. The instructions say to remove material from the bottom of the top skin and the top of the bottom skin. Is there a reason for sanding the bottom of both skins?
 
My suggestion for tapering bottoms was for the plan to polish crowd. Have done this method on a number of wings with great results. Just requires a very slight bend introduced along the diagonal taper line on the underlying skin.
 
As in folks that like using products like Rolite, Met—All, Blue Magic, Maas, AP or similar to make shiny mirror like planes without having different results in shine between the 2024T3 top pure aluminum layer compared what can be achieved in the alloy layer in the core of the sheet.
So read it as referenced to polish (aircraft finish), not Polish (friends)
 
I clamped the skin to the corner of the work bench using a piece of angle aluminum at the diagonal I wanted. Used a combination of file and hardwood sanding block. Go slow and check the edge frequently to avoid getting it too thin. I also used a caliper to check thickness on the first go at it but ditched that afterwords. I did as the plans state top of the bottom skin and bottom of the top skin.
 
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