Spar Preperation

[Seansull]

Hi Glen,

I found tapered sanding cones on a mandrel the most time efficient way to initially smooth out the tooling marks. I buy these in bulk at harbor freight, about $25 for 30 or so. After I smooth all of the marks, I come back with the scotchbrite wheel to polish up the edges.

Here is a close up of the finished product...

Hope this helps!

[psalter]

Glen,

It is always best to have a smooth surface. Small nicks and scratches can be "stress risers" especially in high stress areas, might be sources of cracks later in life. However, it is rare to have a perfectly smooth surface, typically on military aircraft we blend the area out about 10 to 1, or 10 times wider than it is deep.

One of items I like to use is a right angle air die grinder with a green scotch bright disk on it. The scotch bright pad is just enough to smooth, but not to aggressive. Like this http://www.harborfreight.com/complete-s ... 43029.html or http://www.harborfreight.com/pack-of-5- ... 99985.html. They can also be used with a drill, but that can be awkward, It leaves a nice polished edge, and can get into the large interior areas like you show. Tighter radius's are harder, use the largest radius drum you can fit, or emery paper. Small radius drums like you said can be hard to get a smooth surface.

[GlenNJ]

I'm preparing the .1875" spar doubles on my horizontal stabilizer for assembly. The edges are pretty smooth, but there is a slight ripple effect, left by the machining process. Do these surfaces have to be made perfectly smooth? I watched a EAA instructional video, and they imply that all surfaces must be smooth. On the front spar, I used a Vixon file on the outside edges, and is was pretty easy to get a smooth surface. The inside edges were another story. I spent hours getting nice edges, on one spar. Is there a quicker way to dress these edges. I tried a dremel tool with a small sanding drum attachment. It worked, but had a tendency to hop, and I had to be careful to keep it from digging in. I had more success, with a small file, then using 50 grit, to 120 grit sandpaper, and finishing with emery cloth.

Glen