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Lathe motor getting too hot

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  • Lathe motor getting too hot

    I am not exactly sure what I can do about this situation but the motor on my lathe is getting too hot and tripping the OL breaker

    It usually starts happening after maybe an hour of turning, I usually have to back off my DOC or it starts tripping alot.

    Last night I had it running for a couple hours and it was tripping. I felt the motor with my hand and it was hot!

    Currently it is connected to rotary power however it was connected to a vfd before and the vfd would fault out before the OL would trip.

    I think this is the original motor to my lathe, 1hp 3ph, 1725rpm. I took it to a motor shop to have it freshened up when i re did my lathe. Guy said it was in fine shape.

    Here is a picture, its marked as frame 54j (or 56j, can't remember)

    What do you guys think I can get away with for a replacement motor? I would REALLY like to have some more HP. I really like this lathe but 1hp just doesn't cut it for doing any real work.
    I have a brand new 1ph inverter rated motor, which is about twice the physical size. Would this have alot more TQ?

    Think the rest of the machine can handle 1.5 or 2hp?

    Feedback always appreciated!
    Last edited by legendboy; 05-01-2012, 12:43 PM.

  • #2
    What gauge wire do you have running to your RPC and from there to the lathe motor? How long/far are the cable runs for each of the above? What is the horsepower rating of your RPC.

    Don't you like it when you ask a question(s) and other people reply with more questions than answers?


    • #3
      I can't answer if your lathe can "stand" some extra horses, but if the motor is good, it is simply overworked for some reason. Easy way to check is to take amperage readings with no load, and then again while taking one of your "normal" cuts. See how it compares with nameplate rating. If it is overworked, sure enough it'll get hotter than the hinges of, well, you know.

      The other possibility is a mechanical bind of some kind. Bearings heating and beginning to seize, depth of cut too great, etc... If the machine is mechanically sound and you want to increase your work, I would indeed increase the horsepower of the motor.


      • #4
        To try to ascertain the source of your problem we probably need more information.

        If your lathe is an older one (lets say pre-carbide tooling) and you are now using carbide tooling and trying to run the machine at the higher speeds recommended for carbide tooling, while taking deep cuts it may be that you are overloading the motor. If you were using HSS you would be turning at lower speeds and the lathe would be "geared down" giving that 1 HP motor less work to do to obtain the proper speed for a given depth of cut. Gearing the motor down does two things, first the load on the motor is reduced and second the motor maintains it's required operational speed so the fan is able to cool it adequately. If your bogging the motor down to operate at higher speeds the amperage draw is much higher and the motor doesn't spin fast enough to dissipate the heat generated. If the motor is too hot to hold your hand on it it probably is overloaded.

        Electric motors will generate more than specified horsepower for short periods without harm, however if you overload them for longer periods they will overheat. I suggest using an amp probe while you are turning under load to see if the amperage draw is above what is specified on the tag. If so you either need a bigger lathe or bigger motor if you plan to take cuts at the depth you are currently using or continue to use the tooling you currently use. Some machines were given optional motor sizes when manufactured. Perhaps you can check with the manufacturer or literature from the manufacturer to find recommended maximum horsepower.


        • #5
          "Think the rest of the machine can handle 1.5 or 2hp?"

          i have a 3 hp 3ph motor on my 3 in 1. it takes 3 mm cuts in steel. i have to keep the belts pretty loose, otherwise the work starts slipping in the chuck. the bearing gets tight before the motor even warms up. (its a marathon, that weirdly enough i bought in a pawn shop in prague for 50 bucks.)


          • #6
            The ideal test would be a clamp on ammeter on each phase, both during off load and when under load, this will give you a more accurate picture as to what is going on, also the temperature rise during off load condition.


            • #7
              I have 10-3 running from my 5hp rpc however it is marreted to something smaller, maybe 16-3. Easy enough for me to fix that.

              I am running carbide dcmt tooling, running the lathe at 1500 (max) rpm. Headstock gets warm but never hot.

              I am ok taking .03" DOC (so .06" off diameter) on 1" diamater 12l14 @ .008" per rev. If i wanted to go .04" DOC it would probably trip out on me.

              At a .03" DOC the motor lags down a bit, at 0.04" it lags down quite a bit more.

              I am not too interested in using HSS tooling at this point. I have them, I know how to grind and sharpen them, carbide is just more convenient for me.

              I will collect some more info for you guys tonight, I have an amprobe kicking around somewhere...



              • #8
                Balancing three phase motor connections.

                RPC's produce the third phase and it may not be balanced with the other two. The winding that is carrying the higher load is a function of the square of the current. Mark your wires 1-2-3 and A-B-C Make you a chart and record the current rotate the connections and continue to record the currents. The best balanced connection is determined by the smallest differences.
                Byron Boucher
                Burnet, TX


                • #9
                  Originally posted by firbikrhd1
                  Gearing the motor down does two things, first the load on the motor is reduced and second the motor maintains it's required operational speed so the fan is able to cool it adequately. If your bogging the motor down to operate at higher speeds the amperage draw is much higher and the motor doesn't spin fast enough to dissipate the heat generated.
         The load is always the same, plus whatever load the gearing adds as losses. Torque and speed changes with gearing. And a 3 phase motor always turns at its maximum speed (depends on pole count), unless driven from a VFD with a different frequency than mains.

                  And how do you "bog down" a motor to operate at higher speeds?
                  Amount of experience is in direct proportion to the value of broken equipment.


                  • #10
                    The 10-3 should be more than adequate, but the 16-3 is way too light assuming it is carrying the load. The smallest I use in my shop is 12 ga.

                    I'd first try changing the 16 ga wiring, but if that does not correct the problem I would seriously consider changing out the motor. Does the rewind shop have a 1 1/2 or 2 hp used single phase motor you could try out?

                    Not to start an argument, but with the possible exception of precision grinders three phase in the home shop is not very efficient as one looses some power in the conversion. There are other arguments for using a VFD such as being able to have better control over the machine's rpm, but if you're still using the gears in the lathe for setting the spindle speed I believe you'd be better off with a single phase motor.


                    • #11
                      I will correct the mains wiring tonight before I start using the machine and see how that goes. I have about 5 hours of turning to do so it will be a good test.


                      • #12
                        Originally posted by Jaakko Fagerlund

                        And how do you "bog down" a motor to operate at higher speeds?
                        I think he means excessively higher spindle speed which would load the motor too much.

                        My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."


                        • #13
                          From the photo of the lathe I believe it is a std modern series 2000. On my 1120 the std motor was 3/4hp, 3 phase, 56 frame and TEFC. A 1hp was an alternate.

                          The motor in your photo appears to be a drip proof (?) style. My feeling is that there is not enough cooling provided for continuous full load operation, and that the TEFC style is much better suited.

                          On my lathe I have it set up with a Teco VFD and have never had it trip. Can't say that I have pushed it as hard you have but I have had the drive train "groaning" at times!



                          • #14
                            Agree with Dr Stan, that 16/3 wire is way TOO SMALL, a real bottle neck!!


                            • #15
                              Try aiming a fan at it with out some type of cooling that motor will over heat easy in a hour or so.