[preacherman]

This is a simple segmented pen design. The key is to have those segments smooth before you glue them together. The smother the ends of your segments are the better the line will look when you turn it down for the pen. If the segments are left with saw marks and globs of glue to fill the cracks it will not look very good. They would not need to be polished but sanded very well.

As far as glue I think I would try med or thick CA. I don't remember where but I saw an acrylic glue specifically for gluing acrylic blocks together.

Edit:

It is called weld on acrylic cement. Sold at PSI. I can't link it from my phone.