Tell me if I'm crazy. I have a D1-3 4 jaw chuck but my lathe is D1-4. There's plenty of meat in the chuck to locate the D1-4 pins and screws, but the cut for the new taper will break into the old D1-3 pin holes. I do not want anything that will harm my lathe spindle. I think I have 5 options:

1. let the break out occur and assume there is still plenty of meat around the taper to support the chuck
2. fill in the old holes with machinable titanium epoxy ($100 for about 1/2 cup of this stuff, but I already have some)
3. weld in the old holes. I don't like this since I don't think it would be a great idea to put that much heat on the chuck body.
4. get a D1-4 plate and mount the 4J chuck to that. I would remove the pins and through bolt it, but I'd just as soon not stick it out an extra inch to do this.
5. forget this idea.

What do you think? I know I could buy an adapter, but right now I have more time than money (and I don't have much time).

On another note, the 4J chuck taper seems to be closer to 2" dia rather than the 2.125" standard for a D1-3 mount. What's with that?

Thanks.