Don't pinch. That is for developed trees. Right now you're working on trunk. So I wonder - what's your objective? Are you trying to grow a bigger tree or a smaller one?
Scott
I was going to try to thicken that top 1/8th or so. are u suggesting chopping it lower? it would take a few years to establish continuous taper if so, yes?The problems I see with the current image of the trunk are a lack of taper in the center 2/3 and a poor nebari. Are you happy with the trunk as is, or are there any issues that you would like to address?
Scott
It really depends on whether or not you're happy with the present form of the trunk. If it were mine, I'd probably not be satisfied with it and would chop it lower to generate movement and taper. It really depends on your vision for the tree.
If you decide to chop lower, I plant my tridents in the ground while I'm developing trunk and in the pot to develop branching. While in the ground, these trees will put on 10' of growth in a single season (at least in Houston). I cut all those way back - that 10' of growth might only generate an inch of trunk that I keep. Have a look at Smokes post on trunk chop 101 - that set of posts does a great job teaching the technique.
Scott
Everyone always wants to chop everything..... This is not a bad trunk. I wouldnt chop this and even if I did, I wouldnt chop it now.
I assume you just got this tree(?) You have no idea how strong it is. Chopping it now might kill it.
Maples back bud easily if they are healthy. It needs to grow.
In any case I wouldnt chop it because you can develop a new leader from the top branches extending out.
I would let to grow wild this year and let it get strong. Maybe wire some of those branches and new leader when they are enough. Next year you can select which branch and leader you want, cut back and work on developing taper and branching.