[SCzEngrgGroup]

Since most work is done in a vise, and you really don't end up with the fixed jaw of the vise mounted off the back of the table, having more movement in the +Y direction just makes sense... that is where the workpiece is.

And look at bridgeport mills; again, not symmetrical in motion... because the work piece (in a vise) is not mounted symmetrical to the table, so it doesn't matter where the center t-slot lies.

That argument doesn't seem terribly compelling to me. Nothing you hold in a vise is going to come anywhere near the physical limits of travel of any good-sized machine. Only a large part or fixture bolted to the table will.

For maximum flexibility, you'd really want the spindle to be forward of the center-point of Y axis travel, to allow plenty of rear over-hang. In reality, many, if not most, machines I've seen have just the opposite.

Regards,
Ray L.