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- Dec 25, 2011
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The rated or recommended horsepower for the Atlas 10" and early (3/8" bed) 12" was 1/2 HP. For the later 1/2" bed 12" it was 3/4 HP. The only thing that running a larger single speed motor will buy you is additional grief if you ever did have a crash. The machine will not work any better and your electric bill will be higher. There is some justification in going to 1 HP on the Commercials if running a VFD. But I wouldn't go any larger.
Avoid the 3600 RPM motors. For one thing, they don't last as long. Although some of the information is a little dated (as far as specific alloys are concerned). the Atlas MOLO contains a fair amount of information on speeds, feeds depth of cut (DOC) and surface speeds for machining metals and some plastics. All of the 10" and 12" Atlas metal lathes have a rated speed range of 28 to 2072 RPM. I suspect that this chart is based on a motor RPM of 1740 (the old standard) but 1800 or 1725 differ by only about 1%, not enough to worry about. You cannot get that speed range with satisfactory operation out of a variable speed motor without keeping the back gears and at least a 2-step motor pulley. The motor will overheat at the slowest speed you would have to run it at. Also, motors over 1 HP usually have a larger frame size than the 56 which fits the Atlas lathes and a larger than 5/8" shaft diameter. So before you rush out and buy your dream VFD system, be sure to check the fine print.
Optimum cutting speeds vary with the material being worked and are usually specified as surface feet per minute (SFM). Spindle RPM required to achieve the desired surface speed varies inversely with the diameter of the work piece (or of the milling cutter or drill). There is a chart in the MOLO showing the nearest standard Atlas RPM versus diameter for various surface speeds. It covers 30 to 500 SFM. The smallest diameter at which the standard Atlas lathe can hit 500 SFM is 3/4". For reference or feel, most steels are machined at speeds between 50 and 150 SFM, and aluminum at 300 to 500. If you use carbide cutters, you may be able to run higher SFM (the figures in the MOLO are based on high speed steel (HSS) cutters) but you do not have to. The machine will last longer if you don't. And is more comfortable to operate (you don't have to think so fast
).
Avoid the 3600 RPM motors. For one thing, they don't last as long. Although some of the information is a little dated (as far as specific alloys are concerned). the Atlas MOLO contains a fair amount of information on speeds, feeds depth of cut (DOC) and surface speeds for machining metals and some plastics. All of the 10" and 12" Atlas metal lathes have a rated speed range of 28 to 2072 RPM. I suspect that this chart is based on a motor RPM of 1740 (the old standard) but 1800 or 1725 differ by only about 1%, not enough to worry about. You cannot get that speed range with satisfactory operation out of a variable speed motor without keeping the back gears and at least a 2-step motor pulley. The motor will overheat at the slowest speed you would have to run it at. Also, motors over 1 HP usually have a larger frame size than the 56 which fits the Atlas lathes and a larger than 5/8" shaft diameter. So before you rush out and buy your dream VFD system, be sure to check the fine print.
Optimum cutting speeds vary with the material being worked and are usually specified as surface feet per minute (SFM). Spindle RPM required to achieve the desired surface speed varies inversely with the diameter of the work piece (or of the milling cutter or drill). There is a chart in the MOLO showing the nearest standard Atlas RPM versus diameter for various surface speeds. It covers 30 to 500 SFM. The smallest diameter at which the standard Atlas lathe can hit 500 SFM is 3/4". For reference or feel, most steels are machined at speeds between 50 and 150 SFM, and aluminum at 300 to 500. If you use carbide cutters, you may be able to run higher SFM (the figures in the MOLO are based on high speed steel (HSS) cutters) but you do not have to. The machine will last longer if you don't. And is more comfortable to operate (you don't have to think so fast
).