These are the reasons I chose the 9 x 20 over the 7x12 firstly the drive system is all belt driven for the speed changes and not motor driven with a speed controller card that burns up if you get a major turning jam up. Next the tail stock can be set over for taper turning, but more importantly you can adjust the tailstock laterally for true parallel turning over the full length of the bed. My machine will cut imperial and metric threads though not the complete range of each but enough to get along with. The lathe has fine feed and threading leavers that work independently of each other. I have mentioned that the machine is in many ways more robust than the 7x12 and the extra size is very useful, because we all aske our machines to handle larger items that they are really not designed to undertake. The cross slide does have an adjustment to remove back lash, but the top slide does not. One not so good thing the feed screw nuts on the slides are Aluminium, but on my lathe the threads are a standard and available in engineers tap sizes though one is a left-hand thread, so I remade each using bronze. The head stock has number 3 Morse taper so you can purchase off the shelf collets that do not cost an arm and a leg. The spindle nose is threaded so changing from a 4 jaw to a 3 jaw chuck is quicker than undoing screws, and just for my personal liking I can fit a six inch 4 jaw chuck on the lathe for those larger projects. There are aa number of flaws with the machine all of them correctable and there are a number of web sites that go through all the modification that you can make to improve its overall working, but none of the mods are rocket science. As for taking back lash out of slide feed screws there are many methods from having two nuts and adjusting the timing been each along the thread of the feed screw found on expensive lathes, my 9x20 cross slide uses the nut tilt method using a separate screw to perform the tilting action. Another method is to cut the nut half way through and squeeze it length wise by doing this you alter the screw timing this can also be found on lathes made to look good on the second user resale market. Split nuts are found in the lathe apron used for engaging and disengaging the apron from the lead screw or the fine feed lead screw if the lathe has one.
