I am doing bushings on an NPK 210 this week. Here is the way I have always done it. To remove it I use a fairly aggressive straight demo torch and make two cuts 180*s off and finish with a pretty petite straight torch to take out the stragglers. I choose my cut locations by bushing wear and retaining pin positions. Sometimes I cut 3 times at 120* but that is usually if two cuts didn't work as smooth as id like on the first bushing. The problem with that is that sometimes I end up scarring the case a little. This isn't always the case. I have worked on breakers with brass bushings ( I think they were Indeco's). And a few hammers that didn't seem to be such a hard press in. I had a tramac 501 mg a couple of years ago that the lower bushing pins came out of and the bushing just fell out during operation. That was an expensive repair. The reason I ask is because this breaker belongs to one of my primary clients. Well, its a little hard to explain. It used to belong to him and was sold off more than twenty years ago with a PC200. And the twenty years is just a guess. That's when I started working for them and the only reason I knew they used to own it is because there has been a few wear parts in their parts room. Anyway, the excavator it was sold with became scrap and the owner just gave the hammer back. We ran it for about six months and it started puking oil so it came back to me for a reseal and bushings since it both needed them and I have been looking at them on the shelf for twenty years Anyway, ran into a bit of trouble with the disassembly when one tie rod came out halfway and then stopped dead. I noticed that that tie rod was a little different than the other three. So I called up the original owner(who retired a few years back) to see if he remembered any weird maintenance with the hammer. He didn't, but while we were chatting he told me that the way to remove a hammer bushing is to weld rings around the inside of the bushing to shrink it. Like you might to remove a bearing race. I have a hard time believing that would be effective. Just too much meat to try to pull in with beads of weld. But, I don't everything so I thought I would ask. Just in case you were wondering, I toyed with the idea of trying it today. But, I get payed to fix things, not experiment. So I just cut them out with the torches. Did pretty good, one tiny little oopsey scar on one cut, one out of five isn't bad. And could tell that the bushings had been done once before ( most likely when it belonged to the company in the first place) and torched out... Lots of scars in those cuts. By the way, that stuck tierod took most of yesterday to get out. But that process would take far too many paragraphs for me to care to type this evening. So, just asking if anybody has a better way of getting them out. Since I did put (and install) in the title, on the bushings that are torched out I always have the same process. Bushings get packed in dry ice and stored in my freezer overnight. In the morning I take my trusty rose bud and heat (one spot only) the outside of the chuck housing until the inside is at 500 degrees F. And then have just a few seconds to drop the bushings in.
So you did NOT try the weld on the inside trick ? Maybe do your 3 cuts at 120 deg. but don't go all the way thru (just gouge) and then weld. So the bushing can collapse easier. Not in the gouges, in between.
The weld trick is what we used many years ago. I would weld a circle around the inside of the bushing one and half times and then wait an hour or so. Usually they would tap out with an eight ounce hammer. That was too slow for some people so I started using a carbon arc with the small rods. As long as the air pressure is up high when you get close to going through, it leaves less of a mark than a cutting torch. Going back in for most of the stuff back then I had access to a 100 ton press. Only used liquid nitrogen when in the field and couldn't bring something back to the press.
You should try the welding trick. The arc is about 10,000 deg's. So there can be a lot of shrinkage on the cold bushing. As for cutting with a torch it helps to preheat the bushing on the inside till it starts to glow. Then you can pull the torch back a little bit and hit the oxygen lever to blow the orange hot steel away. You'll be able to see when you're close to edge easier and just blow the red hot steel out. Gouging with an air arc you can see pretty good but it takes practice. Easy to make a mess if you've never done it. Very loud and a big shower of sparks though. Need to have a clean cutting tip with a torch especially the center hole so it's a nice straight cut. I've left a little bit of the bushing and then used a chisel to turn the bushing and it came out.