A good point here. To duplicate a shaft I measure at tip, joint, and every two inches in between. Perhaps one inch in areas where a parabolic arc is used. When designing my shaft I found the action of a shaft to be very sensitive to slight changes in this area.
The amount LC3 is wanting removed is on the fifty yard line between cutting then sanding or just sanding. Easy to end up with a shaft that isn't round with the slight taper desired. The shaft needs a measurement in the bridge area before making any changes when I think about it, just cleaning and polishing, normal treatment of a shaft, may have it down to 12.75mm or less in places. I have compressed some shafts more than that with just a very firm polishing. New shafts, not something I do to a customer's.
There is an issue we haven't touched on here since the original conversation was just reducing the bridging area. When talking about duplicating a shaft joint to tip there is a question of ethics in some cue builder's minds. I could have easily copied a quality shaft when I was starting out. I spent several months and went through over a dozen cue blanks before I had a shaft that delivered my hit starting with a good blank and designing my own taper. I suspect that my shaft profile is very close to what some others use but I copied nobody.
If a cue builder is still active and another shaft is desired with the same profile as one of theirs getting the shaft from them is something I recommend. There can be good reasons not to, but this should be first consideration. As a general statement, I don't copy shafts unless a cue builder is no longer available.
Hu