I enjoy do-it-yourself projects, so I decided to cut a bottomless portafilter for my Faema. When I got the machine there was an old, nasty, beat up portafilter in the parts pile. Once I finished rebuilding the machine, I ordered a proper portafilter and basket. Problem here is that I have become accustom to using the bottomless portafilter as a learning tool. That tool is especially helpful when dialing in a new machine. So I decided to chop the bottom off of this old reached PF.
I wrenched off the old busted handle and soak the PF head in some Joe-Glo to clean it up and then off to the garage for a lobotomy. The first step is to mount the head on a secure working platform. You do not want this to wiggle around while you are cutting on it.
There are several ways you can go about chopping the bottom off a PF, but what I find easiest is to drill around the bottom of the PF. This easily removes excess material and makes sure you do not cut to close to the inner edge. As you can see from the photo, I ended up using a rubber-padded clamp to securely hold the PF to my work surface.
Next, I put a tungsten carbide cutter in my rotary tool and commence to connect the dots. The closer you drilled your holes, the quicker you will be able to cut between them. Keep that in mind as you drill the base.
A word of caution. Using this type of cutter produces an incredibly fine shaving. Experience has taught me to wear gloves and long sleeves while doing this. Some eye protection would be a good idea as well. This fine metal 'hair' will float on the breeze created by your working tool. It gets on everything and without gloves; you will end up with dozens of these fine shavings stuck in your hands and arm.
Once the base is off, clean up the shavings and move to a ruff grinding stone. Round out the jagged edges but do not get to close to the inside wall of the PF.
Now switch to a medium or fine stone to remove the remaining excess material. This is where you want to make the final shaping of the hole and make it nice and symmetrical.
You could stop here but I like to go one further. I use a polishing stone to remove the mill marks left by the fine grinding stone. This polishes the inside edge and gives it a professional appearance. This is also when you want to remove any burrs around the outer edge. You do not want a sharp base, it will cut your table to pieces when you tamp on it.
Now you have turned that spare old portafilter into working piece of equipment that should provide you with years of service. Just remember to take your time. You can always grind a little more, but you can never put back. Total start to finish, about one and a half hours.