I have posted some information on this forum before about my machinery and have made many modifications to the mill, but this article is specifically about addressing the problem of keeping the X on a round column bench mill when changing the head position. My particular "King" mill has a 19.2" X, 8" Y and 5 3/4" quill travel plus the head travel on the column. This capacity meets all my hobby machining needs. I dreamt of having a universal turret/ram/ knee mill but space and money dictated my choice. I saw this used bench mill on Kijiji and within driving distance. Mill looked a little scuzzy so did a full teardown, cleanup, repaint. Also started plans to make improvements. During operations I find I often raise and lower the head to keep everything as short as possible for rigidity sake and to get room for the boring head, chuck and drill etc. Redialing or edge finding after each head change was required. The question of keeping an accurate X during these changes kept bugging me. Other owners of this style mill have posted opinions on this subject indicating we all want to make one of these basic mills do more than they were originally designed to do - in other words make a silk purse out of a sows ear - well why not! I went through a lot of "what ifs". I established several parameters relative to what I needed my mill to do. First: I don't do work big enough that I need to rotate the head to reach far corners of a work piece, or, even to get it out of the way; Second, if you do rotate the head you relatively loose some of your Y travel range not having a "ram" to compensate (even in a commercial machine shop I seldom had to rotate the head and when I did I always needed to use the "ram" to offset the change in Y reach): and, Third, I do have to raise and lower the head often during machining operations thus a desire to control the X accuracy setting if possible. Having accepted this, it was just a matter of what way to do it. Others have made made very good stand off frames to control the X which also retain a head swing capability but I'm not sure what guarantee of accuracy you will have when you swing the head back and clamp everything up again. Based on my personal "parameters" I chose the non rotating head solution. I know others have thought of fixing the gear rack to the column and using guide blocks (I presume) on the head, so thought I would give it a try. It could always be undone with no harm done. Also the whole mod is basically invisible so the aesthetics of the machine are not altered which is a personal preference. The attached series of photos shows the results of my effort. Subsequent up and down tests show an accuracy of .001". If on occasion I am really paranoid, I can always edge find or dial indicate for that particular operation. First photo shows the purchased condition just for interest. Photo 2 - pinning the rack moving up the column with the assist of a dial indicator as in photos 3 and 4. Photos 5 and 6 show the top and bottom guide blocks bolted to the head - this was done with the head on the column, in position, and using the pre drilled holes in the guide blocks to drill the head and then tap. The last 3 photos show the test results. First with the head at the bottom and after a X and Y edge find setting the DRO to zero. The second to last photo is with the head raised 5.5",quill extended, and table brought back for X and Y edge find to see how it would compare to the DRO - .001", and last photo is with quill retracted and head back down and another edge find comparison to the DRO - .001". I,ve added one photo of the top guide block showing the slightly modified middle pulley bracket to accommodate the movement of the bracket when loosening and tightening the belts. I welcome any comments.