Originally Posted by rockm

If you want a thicker trunk, the tree shouldn't be pruned anywhere at all for a year or more. THe more growth, the thicker the trunk will become. A larger container would also aid trunk development, as would refraining from root pruning.

In other words, put the tree in a container a third bigger than the one it's in now and let it alone for a year --or more--to get some size on the trunk.
Pruning is working at cross purposes if you're after a larger trunked tree. Branches on smaller trees are usually removed completely and new branches regrown after the trunk is developed to the size desired. Branches are expendable and renewable. Trunks are not. A good bonsai IS a good trunk. Branches are secondary concerns.