It would help if you would identify which type you are referring to.
The first style pen I made was the American Classic by Woodcraft.I made a jig to pull out some components while others could be "pressed" out and still others required a long punch, good grip and friendly persuasion.
Slim lines are easier but still require a good grip and "friendly persuasion"
Take a slime line and separate it at the middle.
Go to a "real" hardware store and find a rod that will slip through the top of the transmission and is log enough to reach the tip(nib)
Here's wher the good grip and friendly persuasion come in.After inserting the rod through the transmission grasp teh pen barrel firmly and whack the top of the rod till the nib flies off usually across the table.(also to the floor)
Once the nib is off insert a 1/4" bolt or rod through the nib end and using a block with a 1/4" hole you can press the transmission out on the Dp,lathe or pen press.
USe the 1/4 rod or bolt to whack out the cap stud and clip.
There are pen dissassembly tools available through most kit suppliers but I found a set of long punches at Harbor Freight at a much lower cost.
Euro style pens or any other that have glued components are trickier because the center rings are sometimes glued on.
As you need to take more pens apart it gets easier and you will probably find short cuts.
