Okay, Jason, I been in your shoes so here's the cheapy, down and dirty method. Don't buy a drill press. Don't buy a Jacobs Chuck. Don't buy a disc sander. Buy a sheet of sandpaper and a hand-held paper hole punch.
I'm assuming you're starting off with a Slimline or some other kit that requires a 7MM hole. If not, then this tech nique may need some tweaking.
Hold your blank in the vise on your work bench or clamp it to the bench with C clamps if you don't have a vise. Drill with your electric hand drill. It you don't have one of those, go buy one.
Use big chunks of wood. They don't have to be nice, square blanks. Use whatever kind of wood you have handy - this is your learning curve. If you use nice pretty 3/4 inch squared blanks, you're likely to drill out the side of the blank. Heck, you may do that anyway. So use big chucnks. It gives you a chance to practice your turning skills. Learning to 'turn air' (getting a rough intop cylindrical shape) is important.
Use a hand saw to cut your blanks down to just a tiny bit longer than the tubes.
Sometimes I cut my blanks a whole lot longer than the tube and then (withe the tubes glued in) I turn it down to a reasonable diamter and use a parting tool to cut it down to the edge of the tube. But that's a Whole other matter.
Now, you don't have to have a disc sander and you don't have to make a jig. Buy sandpaper - I'd go with 100 grit. Measure the flat, vertical surface of your mandrell-holder, the round flat part from which the mandrel itself protrudes. Cut some little square pieces of your sandpaper that are a little bigger across than the diameter of the mandrell-holder. Cover the non-gritty side of the sandpaper squares with doublesided tape. Using a common household hole punch, punch a hole in the center of each little square. Hole punchers make a hole that is about a quarter inch in diameter which is the diamter of your mandrel!
Now, slide one little square onto the mandrell and up against the flat vertical surface. Press to make the double sided tape adhere. Slide one of your pen barrel sections onto the mandrell. (You've already glued in the tube and maybe rough turned it.) Hold the your fist around the piece and turn the lathe on - slow till you get used to this. The mandrell spins round and so does the sandpaper which is attached to it. Slide the pen piece to the spinning sandpaper and bounce it against the spinning sandpaper a coupld of time. Turn lathe off and inspect the end. Repeat till you just barely kiss the brass of the tube. ALWAYS turn the lathe off before you slide the pen part off so you're not tempted to try to slide the pen part back on the mandrell while it's turning (Don't Ask Me How I Know This - DAMHIKT).
This down and dirty technique works just fine. Some of my favorite pens were done this way. The whole point of a pen mill is to creater a surface at the end of your pen that's excatly a 90 degree angle from the tube inside. That's what you do with the sandpaper at the end of the mandrell because the mandrell's inside your tube.
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