I didn't realise how bad it was. I thought maybe one cut, somewhere close to under the chuck. But having two, so far apart puts a different light onto it.

A gap bed just isn't feasible, due to the way the lathe is actually made. My new lathe, even though massively built compared to the Atlas, has a gap bed, but as soon as it is removed, all guarantees are down the river, as they can't ensure it will go back in exactly the same position as it came out. The Atlas would just bend like a banana in the middle.

The first option would be the best bet in the beginning, but you would need to ensure that you got a bed to match either the 42" (rather rare) and not have to cut the leadscrew or the 36" version and hope that the person selling has retained the leadscrew to go with it, or you will end up cutting the one you have. If you can find a 48" one with leadscrew, then great, snatch his hand off. The price of a new leadscrew (about 10 years ago) was around £125. I daren't even consider the cost of a new bed. Clausing USA still stock most new spares for these machines. Putting a wanted ad on John Stevensons site would be one option, or trawling ebay for "Atlas 10F" will eventually come up with something that might be OK. I got a lot of bits off there, and even in the last few months, I have noticed a few.

For a repair job, and now having seen it in the flesh, I would cut it off at the weld under the chuck, leaving the cast in bridge next to it intact, then dress the remaining cut off end to the same as the end you have cut off, and put in all the required holes

Doing it that way, you could dress the welded part of the bed under the head down to or below level of the main bed. You can then easily shim up the head to get it back into the right position if you had to go low. Anyone with a mill with a largish table should be able to machine that for you.

With regards to putting in linear rails. I personally don't think you could get a lathe of this size rigid enough with just rails. It would be nowhere as near as rigid as the girder. Once you get over a certain diameter of cutting on a lathe, the cutting forces required can get very large indeed, and do require large masses to keep everything stable.

You said over on the minilathe post that I make it sound so easy. In fact in my eyes, it is a dead easy fix to do, IF you have the machinery to do it, and the experience of fixing large items such as this. I can't help it if I have both. The main problem is I am not there to do it for you, so I, and hopefully other people, will have to try to give you as much info that is required, so that at least you stand a chance of completing it.

John