Uke makes a fist and sticks his arm out to his side (kind of like someone thumbing a lift), nage touches or cups uke's fist and 'makes a line' to uke. I asked Ikeda sensei a number of times to explain what make a line meant, he kept telling me it was just a line.
"Path". Like in "groundpath". No slack in that path (i.e., a good firm connection) or the connection between centers is not there.
So, once I've made my line, I then move my center which displaces uke's center and I can usually see a small movement in my partner as if I've just 'bumped' him a little. Once this has happened, I can move him around, make him fall over etc. How do I move my center? Well, again, finally this year I got some help on that one from Ikeda sensei. I'll try and explain...
You stand kind of relaxed, neutral. You move your stomach in a circular direction, up and forward and slightly down (forward) then reverse (center) then up and back (back) then reverse (center) then up and left (left) then reverse (center) then up and right (right) then reverse. I can't really explain this that well, but after doing this a good few times you feel slightly strange inside... Ikeda sensei said you need to do this everyday, practice, you don't need a partner. I find it great to do when driving, and I had hold of the steering wheel, I *think* I can feel my center moving around and I feel heavier on one side etc. It's almost like the movement body poppers used to make way back when, that line, squiggle, wave form shape.
He's also done the same exercise with him sat in a chair to me...
This is all probably badly explained but it's all I've got to work on at the moment, again, I'll say I can get this to work on my students and visitors to my club but I'm really not sure exactly how it's working. I've tried to explain what's in my head when I'm doing it based on talking to Ikeda sensei.
Great descriptions. I think that by putting your thoughts on paper, it's helpful for everyone.
In a way, you can think of Uke as a, say, tubular-steel sculpture and you are a tubular-steel sculpture. A "good connection" or "unity" means that the two sculptures have just become welded together into one sculpture. Think of that now welded-together sculpture as having only one flexible/movable place .... the hara. So it's the hara you have to move in order to affect the two (now one) frameworks. Depending upon the angles that are determined by how and where the bonding of the two scuptures is, where the weak-points in balance for the Uke part of the sculpture, and so on, the hara has to be able to, ummmm, 'motivate' things in that direction. Because there are a number of possible directions you may need to move the hara/dantien/tanden, the hara is going to have to be exercised and trained *as part of the unit*. Just being able to move a dantien in isolation means nothing, in reality.
I can't understand exactly from your description how you're practicing the hara/dantien/tanden movement, but it's one of those things that is almost impossible to convey in writing anyway, so I'll show the traditional method to you in Edinburgh, lord willing and the creek don't rise.