This article includes two short video walkthroughs (1:16 and 1:52).
Quick answer
If the cylinder removal device isn't separating the base, remove the set screws so the cylinder can spin freely, then twist it loose while lifting. On a 4-spoke base you can use the base itself as the lever. For a really stuck chair, a large pipe wrench (about 18 inches) on the cylinder gives you the leverage you need.
Option 1: 4-spoke base, Allen tool only
Raise the chair all the way up, then flip it over and tip it forward.
With the Allen tool, loosen and remove the two set screws so the base can spin freely.
Hold the chair steady with your legs and use the base like a big wrench. Turn it clockwise or counterclockwise with a little back-and-forth wiggle until it breaks free, lifting out at the same time.
Option 2: really stuck, use a pipe wrench
Get a large pipe wrench, about 18 inches. A small one won't give you enough leverage.
Flip the chair over and remove the set screw with the Allen tool so the cylinder can spin freely.
If you can, slide the collar up and out of the way. If it won't move, leave it.
Set the wrench deep in its jaws on the cylinder, grip far out on the handle, and twist. Once the cylinder spins, repeat a few times while lifting, and it comes right out.
Also called: base won't come off, stuck cylinder, can't separate the base, pipe wrench, 4 spoke base removal.
Video transcript: stuck 4-spoke base
Okay. I'm going to teach you how to take your four-spoke base off of the chair with just an Allen tool. We're going to start by making sure that the chair is all the way up in height. We're going to flip it over, tip it forwards, grab your Allen tool, and focus on these two set screws. Now, if you've been using these two and it hasn't broken apart, that's alright. Here's a cheat code for you. We're going to loosen these up and then take them out. Just get these out of the way. And now the base can spin freely.
Now, I prefer doing it this way. I get down here and hold on to the chair with my legs, and then I use the base like a big pipe wrench. You can turn it clockwise or counterclockwise, but you've just got to get it to spin freely, and it breaks free. Just a little back-and-forth wiggle. Really easy, and I lift out at the same time. It comes off just like that.
Video transcript: pipe wrench
Hi, guys. I'm going to teach you how to take your chair apart when it's really stuck, and the Allen tool and the cylinder removal device just aren't getting the job done. What you need is a big pipe wrench. I picked this one up from Harbor Freight for $8.99. Most local hardware stores are going to carry one of these. If you're going to go out and get one, don't get a little pipe wrench. You won't have enough leverage to break the cylinder from the base. Go for a bigger one. This is about 18 inches, and it's about the right size.
All you do is flip the chair over, get your Allen tool out, and bring your pipe wrench with you. We just need to take this set screw out right here so that the cylinder can spin freely. I'm going to break it loose, flip this over, and take the set screw all the way out. If this moves freely and I can get it up and out of the way, that's better. I can put the pipe wrench right here. Sometimes they get stuck, because this is a nice tight fit as well, and it just won't go up. That's fine. Leave it there.
Put the pipe wrench right here and adjust it open until you get it nice and deep into the jaws, and grab all the way out here. I've got to tighten mine a little more. There we go. Just reach way out here and give it a twist. If this part is spinning with the wrench, you're already winning. Just do that a few times and lift out at the same time, and it comes right out. $8.99. Quick fix.