Just to add to this that before i start on the finish of the pen i sand off the edges to be certain that they are as square as possible so that they come together correctly when assembling the pen .. Here is how i do it ..
I use two old mandrels, one that i have had squared off and stuck velcro to it to hold the sandpaper, the one in the tailstock holds a rod that fits tightly in the 7mm tubes
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