Spar Preperations Prior to Riveting

[mayo3808]

Great job Ron your spars are really looking good.

[RonFranck]

I added another photo to the end of the album showing my spar drilling setup using a bench-top drill press.
The support blocks on each end have a thin, white piece of plastic stapled to the top surface. This allows the spars to slide freely back and forth as the spar is positioned for drilling hole to hole. The plastic can be cut from the side of a empty plastic jug.
Handheld drill motors, no matter how steady you hold them just don't produce quality equal to the drill press, at least not in these tired, old hands.....

Cheers, Ron

[GlenNJ]

Ron,
I did my spars the long, tedious way with files, sandpaper and scotch brite pads. Your techniques looks a lot easier and quicker. If I had to do them again, I'd finish them like you did.
Glen

[woolleys]

Ron, outstanding information. Excellent post.

[RonFranck]

I have not seen a lot of detailed, close-up photos on prepping the spars prior to riveting so I thought I'd try my hand at posting a few. First, a few words.....

The 1/4" spar plates have a lot of machined surface that needs some attention. The radii are pretty good right out of the box but still they need some attention to remove anything that might become a stress riser. I considered a Dremel motor tool with a small sanding drum but early trials were less than optimal. The drums wore out quickly and plugged up with aluminum debris, and they are a bit expensive to replace often. There seemed to be very few commercially available options so I decided to try make something of my own. I took a section of 3/8 wooden dowel and cut a slot in one end to hold a strip of sandpaper. To keep the sandpaper from unwinding I wrapped a few short pieces of tape around each end. I made two of these, one with 220 grit paper, the other with 320 grit paper. If you use two drill motors it will save you time and effort changing out drums as you progress with finishing each radius.

The other commercially made item I tried were the small discs that are used in a die grinder, both fine grit sanding pads and the Scotchbrite fabric pads. I found the sandpaper type too aggressive. Using the Scotchbrite style pads, the fabric seemed to fuse or melt together. I needed something better. After some experimentation I happened to come across a 3-M Scotchbrite product made for metal. I cut out a couple of circular pads from the 3-M product and hot glued them to a few used discs. Although they do wear out faster than the commercially made discs (possibly due to the many sharp edges on the spar webs,) they do not fuse or plug up and leave a very pleasing finish to the aluminum. When they wear out I use a heat gun to soften the old hot glue and the old fabric lifts right off. The disc can then be renewed with a fresh bead of hot glue and a new pad. The pictures tell the story.

To clean up the tool marks on the spar webs I use a short piece of 1" x 1" solid aluminum bar stock wrapped first with 220 grit paper, followed by 320 grit paper and finally free-handing the surfaces with 400 grit for the final polish.
This might sound to some that I'm taking this finishing thing a bit too far, but that is where my level of comfort took me I have peace of mind that I did a proper job of eliminating any chance of developing a stress crack. It takes a liberal application of elbow grease, but the results are worth the effort.
I hope these meager, few photos help other builders as they progress through the early stages of construction.

I hope this link works....

https://photos.google.com/share/AF1QipN ... hxQ3V6dFNB

I also recommend using a benchtop style drill press to up-drill your holes. Much easier than anticipated and better results are obtained over that when using a hand held drill motor.

Good luck, Ron