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Carbon fiber boom mounts
This is a small series of photos detailing how to make carbon fiber boom/tube/rod to sheet, block or other flat surface interfaces from balsa. This is exceptionally useful when you're trying to mount tail feathers on a carbon fiber boom, something a lot of DLG builders need to do.
NOTE for the best mount, sand the groove across the grain, not with it. If you make a mount with the grain it'll tend to split.
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You'll need a balsa stripper, I like the MasterAirscrew one, a cutoff or sample of your desired carbon fiber boom. Some 150 grit sandpaper or what ever you have handy and of course some suitable balsa.
For the sake of this photo series, we'll be matching 6mm carbon fiber boom with 6mm soft Balsa.
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Start by wrapping the sand paper over the carbon fiber boom (just once, don't try roll it up). Now, hold down that sand paper really hard so that it basically forms a friction hold with the carbon fiber boom. The carbon fiber boom and sandpaper will not be moving.
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Now, move the balsa block back and forth sanding it down until you get a reasonable scallop. I suggest then turning the block over and doing in the opposite direction, this will help counter any thickness/offset issues induced by the sandpaper being wrapped around the boom.
Keep going, nearly there. It doesn't take long to do this, typically 30 seconds to 2 minutes, don't rush it. When you sand the block down, make sure that it keeps constantly against the carbon fiber boom.
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Okay, we're done. Take a breather, have a cup of coffee or a beer... or some water. Admire your work.
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Now here's where the 'smart' bit comes in. Line up the carbon fiber boom + balsa block again, this time without the sandpaper. They should fit together reasonably well.
Wind out your balsa stripper so that it's going to cut wide enough for the carbon fiber boom (6mm) and what ever offset you want the balsa to be (ie, 3mm) (total of 9mm).
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Once again, no moving of the carbon fiber boom or the cutter, just move the balsa block through the blade, holding the cutter and boom steady (my other hand doesn't show because I had to hold the camera)
If you're using the balsa in the cross-grain configuration you will have to do multiple passes of the balsa stripper at ever increasing cut-depth.
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Bravo! You've done it, look at that nicely sliced boom->sheet interface.
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Look at it a bit more. You'll notice there appears to be a bit of uneveness with the placement of the groove relative to the center of the balsa, don't fret! The purpose of this whole interface is to ensure that the boom is parallel to the surface that we're trying to mount it to, this block will do that despite the slightly non-centered goove.
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Finally, take your new boom interface block of balsa and place the sample piece on it and check that it does indeed sit parallel to the surface - as you can see, it is.
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