Dumb question from me. If you have a lathe, why not make a bush? You wouldn't need to ream the hole, just bore it to size. But First check the shaft, perhaps clean it up with a cheap diamond lapping stick from the 'pound shop' or fine file and emery cloth. Do this and you will appreciate your lathe more as it will have become part of you.
BobH

there should be a small hole at base of the shaft to allow oil to get between the shaft and the key bearing bush – suspect too little oil in past and maybe ran dry – and thus hot -with luck + oil should be salvageable

If it was mine, I would refit the stub shaft in the arm, secure the arm in a vice with the stub pointing upwards, replace the big gear on the bush with the key in place, then soak the bush with Plus Gas and try to turn the gear back and forth. The extra leverage gained by gripping the rim of the gear could be enough to start it moving, then it's just a matter of time and perseverance . . and plenty of Plus Gas . . to get it spinning freely.

If that doesn't work first time, leave it overnight to soak and keep trying. I've freed up many old bits of machinery using similar methods. I would only use heat as a last resort.

Mike.

Other penetrating oils are available

Just be careful if you use the sector arm as a wrench – Its probably made of cast iron (or even aluminium) and will easily shatter.
BobH

I mistakenly assumed that it wasn't from a Sieg because as Neil has pointed out the banjo is different from that on my SC3. Apologies.

Martin

I had the same problem on my Sieg a while ago. Like Mick I was able to get it all apart. After cleaning it all up I greased it all. Obviously needs to be lubricated every few hours of running, particularly if the run is fairly continuous as the bush and shaft appear to be similar metals ie steel..

Mick – the hole for the screw shown in your photo – does it connect to the cross drilled hole? If so maybe you could make an adapter with same size thread as the screw to go on your oil or grease gun. That way you could pull out the screw and give it a fresh shot of oil or grease periodically. It will probably never seize again if you did that.

If the holes do not connect maybe you could drill end hole through to cross hole so it does, or drill and tap the other end to do the same idea.

To prevent recurrences in the future, why not remove the gear from time to time and lubricate the shaft and bore?

Any time that you are changing the gear train, for screwcutting, this provides an ideal opportunity.

If you do make a new bush, why not use brass or phosphor bronze? Running steel on steel, or any other like on like materials) is asking for a seizure.

Howard