something to consider, how you raise your sword up affects how you cut down. the amount of muscle you use to raise your sword, is the same amount of muscle tension you have to overcome while cutting down (muscle fibers always pull, not push). tension often what is causing the wobbliness in the cut. that means the less muscle you use to raise, the less you have to deal with when you cut down. one other thing to consider, folks tend to think about stopping the blade while cutting, and usually trying to stop the blade with the right hand which contributes to the wobbliness. imagine that you have a third hand (won't use the third leg image
) ) that sticks out from your hara to stop the blade.
so starting and stopping are, for me anyway, the things that make the blade wobble during the cut. interesting isn't it that the beginning and ending messing up the middle.