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  #1  
Old 09-26-2021, 07:00 PM
stefanj stefanj is offline
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Default Centuri Fin Overbite

I restarted a long-delayed build of a Semroc Centaur. This is a reissue of an old Centuri kit.

I ran into a problem that's plagued me with a lot of Centuri designs. The double-swept fins are made of two parts, allowing a sharply angled leading edge. I round the fin edges first, then assemble them.

Despite taking care to keep things even, I ended up with the situation shown in the attached photo. There's a kind of overbite or underbite.

Any suggestions for how to even things up? I'd rather build up than sand down.

Lots of putty? Tissue wraps?
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Old 09-26-2021, 08:45 PM
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erik442 erik442 is offline
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I get around that by gluing both fin halves together first, and then rounding the leading edge.
IIRC a small amount of filler was needed, but I was able to minimize the offset by matching the edges before gluing.
If it looks like that might happen, I cut the smaller inboard half slightly oversize then sand it back to meet.
At this stage it looks like you could flatten the leading edge of the short side then add a small strip of balsa and re-round the leading edge.
Otherwise it's filler.
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Old 09-26-2021, 09:08 PM
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BEC BEC is offline
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Quote:
Originally Posted by erik442
At this stage it looks like you could flatten the leading edge of the short side then add a small strip of balsa and re-round the leading edge..


Yup, that seems to me to be the best answer, too. The scrap sheets from which the fins were cut of course can provide the necessary stock.
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Old 09-26-2021, 09:32 PM
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ghrocketman ghrocketman is offline
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I always glue them together first also.
Glue then Sand and the issue is nearly non existent.
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Old 09-27-2021, 08:06 PM
DavidQ DavidQ is offline
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A couple thoughts on your techniques:

1) If you want to sand before joining, consider aligning the leading edge instead of the trailing edge. Then, if there is overhang on one of the trailing edges, it can be sanded away instead of filling the leading edge. More specifically, I would recommend aligning the edges on the concave angle, which are the leading edge in your pictures.

2) If you join the pieces before rounding the edge, use an emery board to round the edge with the concave angle. You can get really nice boundaries where the two rounded edges meet. At least I get better results than I would get when just using sandpaper.
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Old 09-28-2021, 12:34 AM
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ghrocketman ghrocketman is offline
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+1 on that emery board tip.
I do the same
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