I've been told - you really really want to have a cover for precision machine tools if the workspace is mainly a welding and metal-fab. space.
Best wishes to you all and a happy Christmas, Rich S
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I'd look at the diameter and length of parts of the ore processing equipment you might be building or repairing. My 10" diameter capacity lathe is too small to refinish its own speed reduction pulley, or my brake drums and rotors.
Unless you need to turn long solid rollers a lathe with some bed wear might be acceptable. Usually the tailstock end has less wear and could turn each half of a roller or thread the end of a shaft. My little lathe had over half a mm wear in the ways near the chuck which didn't affect the small tools I made with it.
The spindle bore is important when turning the ends of long shafts to fit salvaged or rebored pulleys or gears. The slowest turning, highest torque shaft on my sawmill calculated to 1" OD for mild steel fatigue life at 10HP. That happened to be right for the metric chain sprocket I turned and splined the shaft to fit.
The precision slides are bare steel. Machines left outdoors rust quickly, I was lucky with the surface grinder because its ways are shielded from grinding grit (and rain) and it could clean up the top of its magnetic chuck. I still had to buy or make some replacement parts.
A lathe and mill are necessary, a surface grinder not so much but for $100 I couldn't resist. It's probably saved several times its cost by resharpening high quality endmills and large taps I bought dull and cheap. For me the other essentials are a horizontal bandsaw and a bench grinder which shapes and sharpens HSS lathe bits, my old, slow, worn lathe isn't happy with carbide. The vertical mill is a fine drill press. Many have found the 4" x
6" bandsaw too troublesome and bought larger though mine is OK with some changes. The 4x6 with a very coarse blade cuts 150mm (6") square timbers neatly enough to expose the cut ends in a retaining wall.I also have a horizontal mill which is less versatile but more rigid and cuts considerably faster, and an abrasive chop saw for harder steel such as rebar and tubing too thin-walled for the bandsaw until I found a 32 TPI blade. A belt sander is handy for deburring sharp edges, a small portable 1" x 30" model is enough for me and claims no permanent bench space, like the chop saw (and often the bandsaw) I use it outside.
A 4 jaw lathe chuck will do everything, including hold a smaller chuck that grips small rods or even a drill chuck for very fine work. Centering a shaft in one is slower but more precise than a 3-jaw, especially a worn one. Part of my qualification for optical work was showing I could center a 4-jaw to 1 micron, another was hand writing my name 0.5mm high. I can carve straight strokes but not curves 0.1mm high, to label an IC bonding pad on the silicon wafer.
1 micron is 0.4 divisions on an indicator graduated to tenths of 0.001". I have a B&S BesTest graduated to 0.00005", 1.25 microns, $25 at a second-hand tool store.5C collets are very nice, partly to avoid the danger of spinning chuck jaws. You need only the collets for standard sizes of rods and shafting. Work held in them can be moved between the lathe and milling machine for indexed cuts. My small 3, 4 and 6 jaw chucks are on 5C mounts for that purpose.
The lathe makes circular and rotating parts, power transmission, the mill sliding or stationary ones, the frame. A lathe can be rigged to cut keyways, flats on small parts or splines before you find a mill. Either can cut mathematically defined curves or tapers by making an X-Y table with a spreadsheet and then filing to the bottom of the cut marks.
A digital readout isn't essential especially for one-offs and repairs. My home machines don't have them, I measure how far is left to go and cut most of it by the graduated dials. This minimizes the effect of wear and shows if I need to resharpen for final surface finish. jsw