Sometimes when I wear a raglan-sleeve sweater or dress I have made, a fellow knitter will remark on the lack of bunching at the underarms. They will then go on to explain that, whenever they try the raglan construction, they are always plagued by this unsightly problem. Do I know why that is?
Without seeing the garment they'd made, I could not really say, other than perhaps a too-shallow yoke depth could be the culprit (this post from Fringe Association explains this pretty well). However, a recent encounter made me aware of another possibility.
A few days ago, I was chatting with a local knitter and she mentioned the raglan-bunch. Frustratingly, she's had this same issue with several sweaters now, and making the yoke deeper did not seem to help.
Curious, I asked to have a look at the patterns she was using. And in terms of the raglan shaping (top-down), the instructions in all of them read something like this:
. increase for the raglans every other round, until so-many body and sleeve stitches are attained
. then, work in pattern (no longer increasing) until the yoke is deep enough to separate the sleeves
I looked at the instructions, then looked at the knitter, and finally it dawned on me what the problem was.
These instructions, while perfectly typical of raglan construction, result in a yoke shape that favours broad or squarish shoulders - that is, shoulders which widen fairly rapidly.
Unfortunately, for those who have narrow, or sloping shoulders, this shaping will result in too much fabric being created too high in the yoke - leading to bunching.
If you suspect that this might be the problem for you, try re-writing the yoke instructions given in the pattern as follows:
. increase for the raglans every other round, until 75% of the suggested body and sleeve stitches are attained
. then, increase for the raglans every 4th round until the full suggested number of stitches are attained
. finally, work in pattern (no longer increasing) until the yoke is deep enough to separate the sleeves
This will result in a more gradual raglan increase, favouring those with sloping or narrow shoulders.