Okay experts, what is the difference between a drill-mill ans a mill ?
My round column allows me to swivel the head completely away from the bed and use it as a drill press or to mill something too big for the bed. I can groove tires with it(as an example).
I can fly cut some very large things with it.
I don't have a square column machine but imagine with a LOT of work and lifting they would do the same...or maybe they have a pivot in the base somewhere....
These 2 topics (mill-drill vs mill and round column vs dovetail square) are very closely related.
Expert, feel free to correct me. A mill-drill has a fixed table and the head and quill move up and down for Z-axis adjustments
(full sized machine have a fixed head and the table moves up and down). Typically, there is a coarse and a fine hand wheels for Z-axis movement. The coarse typically moves the whole head up and down while the fine moves the quill within the head.
The head is mounted on a column, either cylindrical or square w/dovetails. The cylindrical column allow the head to be rotated to either side so that if there is clearance next to the mounting stand, your "table" is the floor. Handy especially for woodworking projects where work piece might not fit between the quill/collet/chuck and the table and vice.
Some mill-drills can tilt their column left or right 45°. With people have actually use this feature and going back to 90° takes some work to make certain it is square to the table.
The complaint about the round columns is variability every time you move the head
(not the quill) up or down. The square columns with dovetail have much less variability as you raise and lower the head.
Digital read outs (DROs) are optional on all of these machines. Many have been converted to CNC. Some people have done customization for larger tables and/or more X and/or Y travel.