Touching the tool on a piece of silver steel is unlikely to get great accuracy as it doesn't account for the runout of the chuck. It's also hard to judge when the tool is just touching.

You could make a light test cut with the tool, measure the diameter of what it just cut and use that value to set the tool distance from the centerline. The problem with that is, as you say, once you change the tool you need to do it again. That's why people get accurate toolposts which allow you to change the tool holder, go back to the first one and still have the tool in the same position to within a decent tolerance. Clearly you need one holder for each tool.

Another option is clamp lots of tools to the machine on a plate, then move/offset to each tool position. It's probably only worth it if you're making lots of the same part.

You might be interested in my CNC lathe build log here:
http://www.mycncuk.com/forums/lathe-...onversion.html

One day I might actually use it!