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Horsepower for South Bend 13" lathe?

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  • #16
    Originally posted by boslab View Post
    Most of the machines in work had ammeters, even small ones, how hard would it be to fit one, at least you can see when your maxed out, single or VFD, I've not looked into it but it occurs to me
    Mark
    My Teco 7300 VFD will display current.

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    • #17
      Originally posted by boslab View Post
      Most of the machines in work had ammeters, even small ones, how hard would it be to fit one, at least you can see when your maxed out, single or VFD, I've not looked into it but it occurs to me
      Mark
      Not too hard, really, easiest is with a "current transformer" set up for mains current. Most have a 5A output @ max rating, but they vary. Most old type meters you find for AC current will probably be 5A full scale

      The current transformer is safer than any other means, as the meter and wiring is not "live". The live wires just go through an insulated hole in the middle of the "donut" core.

      If you do that, and put any sort of a switch on the output to the meter, such as to read 3 phase on all legs, you need to SHORT the transformer output when not using it. Never let it be "open" with current on the wire going through the middle. Otherwise it can get a very high voltage on it and cause failures.

      The other way is either direct through the meter for low currents (maybe 10A), or with a special "shunt resistor". The meter must be made to use that value of "shunt resistor". However, the shunt, the meter, and all the wires for them will be "live" with mains voltage.
      CNC machines only go through the motions

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      • #18
        Hi chuckster. My SB13 was made in 1968 and came with a 3 phase 2HP motor. While I love my SB13 there are a couple of draw backs. It will only cut standard threads, unless you have a 100 tooth and 127 tooth conversion, witch is very expensive. The other draw back is the exposed gear train. It can get very noisy. There are better lathes out there. Just say'n.

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        • #19
          You guys arguing flat belt width Vs motor HP are missing the point. This is a machine tool drive whose demand is all over the map not a constant HP process drive where all factors are optimized for reliability and bang for the buck.

          Remember: I advocated using a VFD in conjunction with a three phase motor. Three phase induction motors when run at 10 Hz from a VFD stop and reverse almost instantly (provided the parameter settings are optimized,) a great aid for tapping and spindle reverse threading. The object of low motor RPM's for some operations is to minimize kinetic energy in the spindle drive.

          Anther point is: recall I suggested HVAC junk piles as sources for free (or nearly free) thee phase induction motors? 3 HP motors and below are the most common sizes installed in air handlers serving commercial spaces. My suggestion is based more on operability, utility, and availability than as a suggested drive requirement.

          Any motor over 1 HP may be considered "suitable" for a 12" lathe of a certain age but 2 HP gives your motor agility and "torquey-ness" for stops and reverses at low motor RPM.

          I apologize for not making my points clearer. I usually don't write out every little detail because I'm usually too wordy.
          Last edited by Forrest Addy; 03-23-2017, 12:21 AM.

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          • #20
            Originally posted by Forrest Addy View Post
            You guys arguing flat belt width Vs motor HP are missing the point. This is a machine tool drive whose demand is all over the map not a constant HP process drive where all factors are optimized for reliability and bang for the buck. ....
            OK..... AND?

            The point about torque is really the whole reason FOR the issue of belt width.

            The belt drive IS INHERENTLY TORQUE LIMITED.

            The reason for the HP limit IS a torque limit, So low speed on the VFD for high torque operations like tapping is almost the opposite of the good way to go (and you have even said so yourself), unless you are counting on the torque limit as protection for the tap.

            The right way to get torque is to run the belt fast, and gear down AFTER that. So you would do better to run the smaller motor faster, using back gear, than to run a big motor slow in direct-drive. You'd get 5+ times more torque capability, WITH the slow speed.

            The reverse could be more motor revolutions long. But it would be 5+ times FEWER than that at the tool.

            The worst case for the torque problem is when running the slowest non-back gear speed. Smallest pulley on the drive side, largest on the spindle, slowest belt speed, with the drive torque limited and the small pulley turning that into the least possible foot-lb (N-m) of torque.
            CNC machines only go through the motions

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