Inspired by asc2 asking on my homemade tamper instructable if my bottomless portafilter was a DIY project I grabbed a spare portafilter and headed to techshop to see if I could successfully lop the bottom off. This is a pretty simple project if you've got access to a metal lathe. I don't have one at home so I made it at techshop.
Start by clamping the portafilter in a vise and unscrewing the handle. The factory was nice enough to use loctite or something similar so it was a pain to disassemble it. I was worried that I would ruin the handle so I brought along a rosewood handle that I made a few months ago. I think if the plan was to keep the same handle I would clamp the body of the portafilter in the vise with a scrap of wood on each side to prevent it from getting all banged up.