Jack,
There can be several scenarios at play here, and as I have insufficient information from your post, will paint more than one.
Some materials flare, regardless the surface structure these materials are tied down on. For example, hollow deer hair, tied down to a hard, smooth surface, such as a (thread covered) hook shank will still flare as the thread pressure ‘bites’ down into the material. The routine approach to curb the flaring is to first tie down with hard wraps, then a couple ‘roping in’ softer turns moving up the wing, followed by a couple hard turns at the original tie-in point. Especially on some downwing caddis patters, such as a Solomon Caddis, this approach is effective.
Tying down ‘hard’ hair, such as squirrel tail hair, will not exhibit much flare no matter how much pressure you apply with the thread wraps. Feather barbs generally fall between these two extremes, but are closer in behavior to the squirrel hair.
Material choice matters.
However, even squirrel hair will flare under certain situations. So onwards to scenario two.
Consider you are tying down this hair just in front of a fatter abdomen. The hair forming the wing will have to ‘climb’ the ridge formed by the abdomen, and as a result will angle away from the shank.
For scenario three the same hard squirrel hair is tied down on a level underbody, but in this case it is a ‘soft’ underbody, for example one which has been dubbed. The hard thread wraps needed to tie down the wing will cinch down into the dubbed body. Immediately next to the tie-in point, on either side, an impromptu ridge is formed and yet again the wing material is forced upwards.
Any of the above might apply to your situation?
Cheers,
Hans W
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