Such is the case with most modular tooling systems. You start with the bar or holder, for either lathe or mill, then select the currently needed head. It's a money saver in the long run. One bar, for example, to set up the one 4" head I have, is about $3k, last I checked. It was about 4 feet long. That sounds like a lot, but if you see it the way Sandvik wants you to, you will see that one bar as capable of being used to bore, thread, groove, face, etc. without having to have separate bars. Just swap heads when you need to run a different operation. Naturally if they are all on the same part the money logic fails, but for many production jobs, a single function is all you need at one time. So you can save some money. Often though, you have to consider the fact that if you have a turret style CNC lathe, it has to be able to swing that 4 foot bar around without colliding with anything. Not many lathes can swing it. So there's little use in mounting up 2, 3 or 4 of these bars in the first place. Same deal on a slant bed with a turret. Rarely do you hang a bar out as far as you can, but on that style turret, there isn't a lot of clearance behind the toolholder, so you can't just choke up on the bar like you'd want to to minimize the overhang. Most shops discourage sawing off the excess just to get a tool to index. So what are you going to do with all that extra bar hanging out the front? Chances are it would run all over stuff while the other tools were in the work anyway.
If/when I do need to use the head I have, I haven't decided whether to go the whole dovetail route, or simply weld it onto a bar. I probably won't be buying alternate heads for it. Then again......
