Hi everyone,
I was lucky to have today off and I started to work on my Comet Chaser when I noticed that my balsa fins (in the sheet) were cracked on the ends. I have not cut them out, nor have I sanded them. I was wondering what would be the best way to fix this. I'm thinking of cutting them out, gluing them with wood glue, and then doing the sanding. anyone had this happen before, comments, opinions, suggestions?
Thanks for the help!
These are laser or die cut correct??
In the old days when you traced a paper pattern on the sheet and then cut them out with the hobby knife, you just avoided the 'bad spots' in the balsa. Not an option for you I take it.
My advice is to paper the fins. Pop them out of the sheet, sand in any airfoil you desire, then grab a few sheets of regular printer paper and the white glue. Lay the fin with the leading edge toward the center of the paper, about 1/2 inch from the edge of the paper. Hold it down and gently trace around it with a pencil (this gives you a glue application guide). Once traced, CAREFULLY roll the fin over its leading edge (make sure it doesn't slip on the paper if you can!) so the opposite side is facing down. Trace it lightly again onto the paper. Remove the fin.
Now you should have two mirror images of the fin outline, spaced a little bit (maybe 1/4 inch) apart on the paper. Grab your white glue, put some on the paper inside the silhouette of the fin, and spread it VERY thin... as in as thin as you can get it. It's ok to smear it outside the lines, just make sure EVERYTHING inside the outline is completely coated with a THIN layer of white glue. (you can do both outlines at once or one at a time-- I usually do one at a time because spreading the glue that thin reduces the working time). Stick the fin down inside the outline, press it down firmly, and if you haven't already, go ahead and spread a THIN layer of glue on the other outline, and be sure you get a thin layer on the space between the two outlines as well (over the leading edge). Now, carefully roll the fin and paper over the leading edge and press the other side of the fin down firmly against the glue-coated paper (folding the previously glued paper side over with the fin of course). Now, grab a round cylindrical object (a Sharpie marker works GREAT for this step!) and using it like a rolling pin, starting from the leading edge of the fin near the center, start burnishing the paper down tight to the fin. Basically you're squeezing out all the excess glue, and firmly bonding the paper to the fin. This will remove any wrinkles or air pockets as well (though if you have wrinkles you probably used too much glue-- it's amazing how little glue this actually takes-- just a "big drop" is usually enough for most fins!) Use the sharpie marker like a rolling pin or simply slide the barrel of the pen across the fin, working from the center of the leading edge toward the trailing edge, and out towards the root and tip edges of the fin. Flip the fin and repeat. I use the rounded end of the Sharpie pen to "outline" the fin and burnish the paper down to itself all the way around the fin (other than the leading edge of course which is where the paper folds over) and this basically glues the paper to iself. With scissors, cut out the fin from the paper, about 1/2 inch of paper all the way around it (don't try to cut right to the edge of the fin... let it dry first!) You can usually get at least 2 fins on a sheet of printer paper (depending on size you might get all four!)
Let them dry overnight. Next day, use scissors to trim the fins down to within about 1/4 inch of the edge of the balsa fin cores. Then, using a SHARP hobby knife, carefully trim the paper along the edge of the fin down to the very edge of the balsa wood. This will remove any extra glue that was squeezed out as well. Once the fin has been trimmed of all extra paper, you can do a final "shave" of the fin to remove any stray paper 'hairs'... hold a piece of 220 grit sandpaper down firmly on your work table, and gently draw the fin across it with the tip, trailing, and root edges against the sandpaper, one at a time. Hold the fin at a SLIGHT angle from vertical and draw the fin across the paper toward you a time or two, using light pressure. This will "shave" any remaining paper "hairs" off the edges of the fin along with any stuck on extra glue. Flip and repeat.
This doesn't take much longer to do than it did to type... about maybe 30 minutes or so to paper the fins, and then another 30 minutes or so to cut them out and dress them against the sandpaper. The fins are now ready to glue on the rocket, just like normal. The nice thing is, they're practically bulletproof now, and for VERY VERY little weight gain, and you don't have to fill balsa grain when you're ready to paint... just prime, sand, and paint like you would the rest of the rocket. In addition, folding the paper over the leading edge ensures that it cannot come loose over time from the slipstream of air trying to rip it off during flight...
Once you try it, you'll never go back!
Later and good luck! OL JR
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