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VFD/Lathe Questions

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  • VFD/Lathe Questions

    I've had enough problems with the OEM single-phase motor on my Jet lathe, and having read many good comments concerning the advantages of VFD-controlled 3-phase motors, would like to change out my lemon for this setup. I've read through part of the Westinghouse/TECO FM100's manual, and noted a section that addresses wiring in remote switching. I understand how using the original fwd-stop-rev drum switch (connected to the lever on the apron) to control the motor would result in a voltage spike to the VFD. I've run this lathe for over a year, and the habit of grabbing for the lever is pretty well ingrained by now. Perhaps removing the lever and operating the motor entirely from the VFD's keypad would be less inconvenient than I'm imagining, but wouldn't it be possible to replace the drum switch with one that's compatible with the VFD? Or would it even be necessary to replace the OEM switch, as long as it's wired into the VFD's terminals correctly? I think what's required is a double throw switch, but does it need to be double pole or...???

    The other question concerns the lathe's brake - it shuts the motor down instantly when you step on the pedal - would this cause the same sort of voltage spike as discussed above? These are primary safety concerns - if they can't be worked around satisfactorily, I'm afraid I'm going to have to give up on converting to 3-phase. I have wiring diagrams for the machine, in both single & 3-phase versions. The tough part is finding anyone within 100 miles who's had any experience with VFD motor controls - and the one guy who I have talked with is swamped.

  • #2
    You should be able to make the existing drum switch work the VFD through its control terminals. I have done just that on four different machines. Barring a wiring diagram, you'll need an ohmmeter or continuity checker to puzzle out which sets of terminals on the switch belong to "forward" and "reverse." It might require jumpering some terminals. Take all the wires off the switch while you puzzle it out.

    You should also be able to wire the lathe's foot brake switch to work the Emergency Stop feature of the VFD. Again, a circuit diagram or meter will let you puzzle out what switch closes or opens where when you step on the brake.


    • #3
      The remote switching on the VFDs are usually a control signal of 5-24 volts DC. This control section of the VFD also has terminals to connect a POT or variable resistor so you can speed up or slow down the motor. All you need are some push buttons and wire to run back to the VFD. Most models can use momentary buttons as well so you can use spring return buttons.
      Hit one button to start the motor, another to stop it and another for reverse. Very nice.

      As for your pedel stop, you can just wire another switch or use the exsisting one parallel to the other stop switch. Once the VFD see's a voltage on the stop terminal it will stop the motor.


      • #4 may have a problem if the VFD expects momentary-contact switches (mine does). You won't get that with the drum switch.

        But, I think you'll find that it's not difficult to get used to a new setup. When I put a VFD on my milling machine, I was so worried I would automatically reach for the old on/off switch for the motor, I took the handle off so I couldn't use it. But once I had the VFD pushbuttons wired up, I don't think I ever reached for the old switch, anyway.
        Try to make a living, not a killing. -- Utah Phillips
        Don't believe everything you know. -- Bumper sticker
        Everybody is ignorant, only on different subjects. -- Will Rogers
        There are lots of people who mistake their imagination for their memory. - Josh Billings
        Law of Logical Argument - Anything is possible if you don't know what you are talking about.
        Don't own anything you have to feed or paint. - Hood River Blackie


        • #5
          DB, "Emergency stopping" or "dynamic braking" too many times before a proper cooling period will fry a inverter. Some have external resistors to dissipate the energy generated by applying reverse torque. A motor can be a generator when power is applied and it is turning. This dumps energy that must be dissipated by heat.

          I set my mill up to coast down. That way the air-spindle brake will not fault it out. (until I forget to turn it off after a tool change)

          Most all inverters require dry contacts to turn them on and off. THEY Use internal power, normally 24vdc. Do not apply external power.

          Some inverters have digital speed inputs, you can take two terminals, by applying power to them in binary type mode you can step through programmed speeds. If no modifying speed is needed via a speed pot, this is easier. Two switches for speed control.

          Make sure you buy a single phase in-three phase out inverter if you need one. Not all can do.
          Excuse me, I farted.


          • #6
            Thanks to all for your replies.

            David, I'd just finished reading an older post about external braking resistors, and had decided I probably wouldn't need to program the VFD to stop the spindle any quicker than at least 2 sec. I go through a lot of start/stop cycles during the process of chambering rifle barrels (which probably has a lot to do with the problems I've had with the original motor), so it wouldn't do to overheat the VFD with needless braking. This is a 13x40 machine, with 6" 3-jaw & 8" 4-jaw chucks. So far, I haven't seen the need for running it over 650rpm, even with carbide insert tooling; however, its top speed is 1800rpm.

            At this point, soft starting is a more desirable feature, especially after listening to the single phase motor snap all the play out of the gear train at each start up.


            • #7
              I bet we can talk you through it.

              You would be surprised at how many electricians don't have a clue about anything less than 120 volts. I have met them that work with high voltage all thier life, they don't know how to wire up a 3way switch.

              Feel free to email me if I can help you.
              [email protected]

              I have seen people wire up inverters with the pushbutton controls so they can reach them easily. This allows simplification. I personally think it should be away from chips, fluids and anything else that might get inside and corrupt.short it out. That way, in-wires L1&L2, out three wires T1,T2,T3 or U,H,W. Plus of course the saftey ground.

              Inverters normally come with the faceplate controls programmed to work. THERE is keypad programming you have to do for them thou. Not complicated, each inverter is different thou. Just take the manual and use the sheet to record your settings. Current, accel time, decell time, boost start, control type.. ususally about 50 or more entries you only need about ten or so.

              Not all inverters have faceplate controls.
              Excuse me, I farted.


              • #8
                I converted a Kent 14x40 to a VFD. (3hp.)

                Was able to convert all Controls, Brakes, Reversing Lever and everything to control the VFD.

                This was all with dry contacts (as Mr Cofer mentioned).

                It was nice to be able to remove most all the contactors and crap from the Electrical Box. (Hope I never need to put them back!)

                I made my own braking resistor.

                I often use the lathe for tapping.
                With about 6 start/stops/reverses per minute over a period of about half a hour.
                I was concerned about overheating the VFD.
                It's never been a problem.
                The Braking Resistor never even gets warm.

                I highly recommend it, just takes a little head scratching to figure it all out.

                Tom M.


                • #9
                  Hey Flatlander, this is a project that I may be interested in doing to my 13x40 sometime in the future. If you decide to go through with it could you post the project here on the board noting any problems you had to overcome. I agree with you on the apron switch, all the machines at work use them and I find them very convenient and would like to keep mine working too if I used a vfd. When I got my first lathe it didn't have an apron switch and I just never really liked it with out it.
                  Jonathan P.


                  • #10
                    What you are proposing isn't a problem, or shouldn't be. I converted one of my lathes from a DC drive, it had been severely compromised, to a 5 HP Sensorless Vector Drive. You may want to check out the VFD forum on the PM site, I'm quite sure that this has already been discussed.
                    In the pictures that follow, the first is the lathe before I modified it for apron control. The handle on the right end of the headstock is the original fwd-stop-reverse, and it is tied into the microswitch that is mounted in the case at the tailstock end of the bed. The knob at the extreme left of the QC gearbox controls the pot, which is mounted inside the base cabinet. The parts of the apron control are in the last picture.
                    The VFD has 4 add-on external braking resistors that will stop the spindle from 3950 RPM in less than 2 seconds with the 5-C collet attach mounted. It takes slightly longer with a 6" 3 jaw from 1500 RPM.



                    • #11
                      I specifically did this with my Jet lathe (13X40). I bought a three phase lathe, knowing I'd have to wire up the VFD (TECO) to it before I could run it (no three phase available at my shop). It took some figuring, but I use the lathe's forward/stop/reverse lever, emergency stop lever, foot brake, and end gear door interlock switch to control the VFD. I have been running this way for several years with no problems. I also set the VFD brake time to roughly 3 sesconds as I don't have a braking resistor. This has worked very well. The forward/stop/reverse lever on mine works via two micro switches.

                      You get an emphatic "go for it" from me.



                      • #12
                        I have a Hitachi L100 on my Harrison M300, 13" lathe. Slightly undersized but runs great.

                        The apron forward / stop / run lever operates 2 microswitches on the original electricals. These I wired to the forward run and reverse run logic level inputs. Lacking external braking resistors, I keep the deceleration time at 2 seconds and increase that if running high speeds with a large chuck.

                        One thing I have not been able to do yet is wire in the emergency foot brake. This VFD doesn't exactly have an emergency stop input.

                        What I need to do to overcome this is to have the foot brake switch open operate the forward and reverse run at the same time as this forces a stop condition.

                        The only problem that remains at that point is whether the VFD allows the motor to coast or controls the entire "ramping down". At this point, it controls the entire ramping down and will generate an error if you throw the apron lever to stop and then hit the foot brake (mechanical only at the moment).

                        The VFD is trying to drive the motor while my foot is trying to stop it. Gotta find the right set of coasting options for that

                        I'm rambling here only to perhaps leave behind some things to watch for.

                        You will love the VFD



                        • #13
                          JimH, sounds like I'm on the right track then. Which TECO VFD do you have? When you said your apron lever operates microswitches, did you mean the OEM switches, or aftermarket ones that you installed?

                          I wonder if there's any way to program a FM100 or MA7200 for an extremely quick braked stop ONLY when the footbrake is engaged, yet let the motor coast to a stop within 2-3sec. after a normal 'off' command input via the apron lever? If that could be done, it should be a way around such an emergency stop generating an error. I don't see the need for an external braking resistor in this case, since the mechanical brake would be absorbing the machine & work inertia.


                          • #14
                            NO, I have never saw two decell options on the menus of the hundreds I have installed.

                            TO avoid a error, you must set the machine inverter to "coast" to stop. It shuts the drive down immediately and does not DB at all. Lathe spins to stop normally, unless you step on a brake to "WHOA" it. The inverter holds power on two coils in the motor and dumps the generated other in DB mode.

                            I did one Allen bradley system on a 30 drive carpet machine, racked the dc bus together. The power factor usage went down so as the machinery was paid for in the first year. One would be DB'ing into the bus while another was pulling. Very little loss or inrush. The actual current load of the machine was about a tenth of the previous power consumption. Not to mention a DC 10hp motor and gearbox was about $6500, a Ac motor, gearbox, drive was about $1500. On top of that, I installed imaginary pushbuttons on a computer screen that eliminated about half the hard-wiring on the system. Now, Ac-inverter usage has went up on the machinery. A good thing gets passed around.

                            Most the inverters I have installed are in industrial enviroments, not machine tools. I have three here running my tools. I'm a Industrial electrican, not a machinist or residential wireman.
                            Excuse me, I farted.


                            • #15
                              David, based on how quickly my lathe stops after I move the apron lever to stop, and assuming there's no braking going on with the original single phase motor, I don't forsee the need to program a VFD for DB. In that case, as you stated, programming it to let the motor coast to a stop should let me use the footbrake without generating an error. It's not like I use the footbrake with any regularity - in fact, to date, I've used it only to demonstrate how it works to my dad. I don't like the idea of doing away with all the built-in safety features while in the process of installing a VFD - you just never know when you might need them. Same goes for the emergency stop button - but in that case, I think the suggestion to wire it in parallel with the apron lever stop position would work.