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  • Stepper Motor Power feed for Single Axis

    I am putting back together my 7” x 30” Kao Fong mill after a complete tear down and going through. I want to eliminate the behemoth gear box power feed for the x-axis and replace it with a stepper motor feed and maybe prepare for a multi axis cnc setup. I figured I would start with the x-axis and provide simple power feed capability with the stepper motor and keep in mind the future expansion to all axes. The x axis lead screw is a 1” OD 5 tpi acme thread. It will be much easier to physically fit a stepper motor to drive the lead screw vs a “servo brand” style power feed hanging off the end of the lead screw.

    So my first question is: What would be the appropriate power or torque level be for a stepper motor for this axis? FYI I will belt drive it and have the capability to go from a ratio of 1:1 to probably 3:1 or so.

    Second question: What are appropriate “operator interfaces” or controllers to run the driver board? I saw one guy home built one and programmed a chip to run it, I also saw some cheese ones on ebay, I am also considering putting together a PLC to control and run the driver board / stepper motor. Not really interested on using a PC at this point for this initial phase.

    Last question (for the moment) is: A stepper motor holds position when idle right? So just power it down when you want to use the axis manually?

    For reference:
    My project:
    http://www.flickr.com/photos/[email protected]/

    My Mill:



    Similar Mill:


    Thanks for your input
    Brian

  • #2
    I would rather have a normal power feed unit than some cobbled together mess.

    If you really want to do it loose the stepper and use a gear motor with a clutch.

    If you are planning on converting to cnc, reconsider. The cost to do the conversion correctly is more than the machine will be worth in the end. Find some shops old bridgeport boss with a dead control and start from there.

    Comment


    • #3
      >I would rather have a normal power feed unit than some cobbled together mess.

      Obvious enough, ohh and I don't cobble anything, noting more that I hate than cobbled up junk

      >If you really want to do it loose the stepper and use a gear motor with a clutch.

      I have a motor driven gearbox for a power feed that needs recycling.


      >If you are planning on converting to cnc, reconsider. The cost to do the conversion correctly is more than the machine will be worth in the end. Find some shops old bridgeport boss with a dead control and start from there.

      CNC is an option, not likely though depending on how boring life gets. A Bridgeport would be nice, but not really an option for me.

      Any help on the questions I asked?

      Comment


      • #4
        Then stick with the gear motor and a pwm speed control. Less likely to stall out. Easier.

        Comment


        • #5
          rakort,

          If you are headed towards converting it to CNC then I think this is an excellent opportunity to experiment with a stepper motor drive on the transverse axis. Selecting the size would be a function of how clean the existing lead screw and nut are, plus how hard and fast you would intend to drive the table as part of a CNC set-up. I am sure that the folks in the cnczone.com and other like groups would have some suggestions for the size of the stepper motor. You will also need the driver board, and power supply plus a circuit to create the stepping pulses. Most of that if sized correctly would easily become one of the 3 axes in your CNC conversion.

          Stepper motors are permanent magnet poly-phase motors that draw the most power when they are energized but stopped (the holding position). With no power applied to the phases they turn relatively easily though with a definite cogging motion. If the controller for some reason (and I don't think they do) shorts the individual phases it will be fairly difficult to turn especially at any speed. If you are concerned about the extra effort to manually operate the table through a stepper motor, than adding a clutch might be considered. There are several articles in past issues of the Home Shop Machinist about adding a power feed to a mill. Some of them are fairly clever.

          Judging from the attention you are putting into restoring the mill, I see no reason that you would end up with a cobbled up mess. I would view it as a good way to dip one's toe into the CNC waters, get a power feed on your mill, and learn a great deal. Depending on your scrounging ability, luck, and determination, the economics of it could be on the plus side.

          I say "gofer-it". I would be quite interested if you choose to go this route.

          Comment


          • #6
            Thanks for the input. Your comments are inline with what I was thinking.

            I will do some more digging around on the sizing issue.

            I am interested in building a circuit or buying a controller for generating the pulses to run the motor. Not really interested in it running with with a laptop and breakout board and this point (maybe later if I go down the cnc road)

            After a little research I also learned that a variable reluctance (also referred to as hybrid motor) turn freely with no power, but a permanent magnet will cog when turned manually. Looking around I don't see many people specing their motors one or the other.....more research needed guess. Yes a clutch is an option, but that would over complicate it in my mind.

            Any idea what issues of HSM have those power feed articles?


            Originally posted by ironnut
            rakort,

            If you are headed towards converting it to CNC then I think this is an excellent opportunity to experiment with a stepper motor drive on the transverse axis. Selecting the size would be a function of how clean the existing lead screw and nut are, plus how hard and fast you would intend to drive the table as part of a CNC set-up. I am sure that the folks in the cnczone.com and other like groups would have some suggestions for the size of the stepper motor. You will also need the driver board, and power supply plus a circuit to create the stepping pulses. Most of that if sized correctly would easily become one of the 3 axes in your CNC conversion.

            Stepper motors are permanent magnet poly-phase motors that draw the most power when they are energized but stopped (the holding position). With no power applied to the phases they turn relatively easily though with a definite cogging motion. If the controller for some reason (and I don't think they do) shorts the individual phases it will be fairly difficult to turn especially at any speed. If you are concerned about the extra effort to manually operate the table through a stepper motor, than adding a clutch might be considered. There are several articles in past issues of the Home Shop Machinist about adding a power feed to a mill. Some of them are fairly clever.

            Judging from the attention you are putting into restoring the mill, I see no reason that you would end up with a cobbled up mess. I would view it as a good way to dip one's toe into the CNC waters, get a power feed on your mill, and learn a great deal. Depending on your scrounging ability, luck, and determination, the economics of it could be on the plus side.

            I say "gofer-it". I would be quite interested if you choose to go this route.

            Comment


            • #7
              Stepper Motor

              Remember when you rotate a stepper motor, it becomes a PM generator and will feed power back into the drive circuit. Not all controls can handle this operation.
              JRW

              Comment


              • #8
                Yes I have been duely warned and understand the issue...thank you for your feed back.

                Rak

                Originally posted by J. R. Williams
                Remember when you rotate a stepper motor, it becomes a PM generator and will feed power back into the drive circuit. Not all controls can handle this operation.
                JRW

                Comment


                • #9
                  Mill-drill power drive article in Machinist Workshop

                  Rakort,

                  I found one of the articles, actually a multi part one spanning 7 or 8 issues starting in April 1999 (volume 12 number 2) by Ed D. Cox. There was another one which was not as elaborate but I haven't run across it yet.

                  I still like the idea and I may build one for my Grizzly floor mill. If I ever get my Bridgeport project going again it will definitely need some sort of power feed.

                  I found this web site/blog. The author is using/mounting servo motors. Not suggesting that you use servo motors, but his mounting system may give you some ideas.

                  http://www.cnccookbook.com/CCBlogJan2009.htm
                  Last edited by ironnut; 08-24-2011, 12:33 PM.

                  Comment


                  • #10
                    If you are going to CNC it later on and want to use steppers to drive it I would consider building the mechanics into the machine now and housing a control box that will ultimately have enough room for all of your drives and power supply needs. When I've done this type of thing [professionally but not with machine tools] I lay out the panel and drill it for the extra drives and wire them in ahead of time using the one drive that we bought as a template. Judging from your restoration work you seem methodical but I dont know how well you are with electronics.

                    So now you have a control box that can accept your Mach3 parallel port input for 2-3 axes that is mounted to your machine and wired to your one stepper. All you need now is a box that will output the step and direction signals to the parallel port as an intermediate stepping stone until you get your PC running.

                    You can use a microcontroller to do this easily and I'd recommend an Arduino since they come with free software and are USB programmable. There is huge community support as well. Write a program that takes in a Potentiometer input via analog and converts it to a scaled pulse train, and then gate that with a "Fwd-OFF-Reverse" switch and you are done. You could do it with a 555 timer and some logic gates too, but I'd only do that if you are more into electronics than programming. I'd do the microcontroller myself but I like to program in C/C++.

                    I need to do a power feed on my lathe and this might be a good solution for that until I CNC the beast.

                    KEJR

                    Comment


                    • #11
                      Agree, plan for the future, I haven't selected a drive / power supply yet, but if possible will make an enclosure suitable for three axes. I'm an engineer in a heavy industrial environment and we put together a lot of drive and control packages....and they always grow over time. Leave room, I hear ya.
                      Methodical is one way to put it! Some may say compulsive, some anal....LOL Electronics I taught myself years ago, but tabled that hobby...am picking it back up now...it came back fast.

                      Arduino was the answer I have been searching for. I was thinking about a PLC, but knew that was too expensive and overkill. I have since purchased an UNO and a few parts from radio shack, dug out my electronics parts box and bread board and I am styling. I will post a video on my flicker page to show you my learning / demo package. I am running a small dc motor to prove the concept, but it has close to all the functionality and more that a typical power feed. I will just update the code accordingly when i bring the stepper into the mix....which wont be too hard.

                      Couple of things I am exploring now is an LCD display for the Arduino. It will be for information display and I am looking into a photo reflective sensor that I can sense the spindle speed and display it. Should work nicely with the vfd.

                      thanks for the advice KEJR. Arduino is the hot ticket.

                      Rakort

                      http://www.flickr.com/photos/[email protected]/


                      Originally posted by KEJR
                      If you are going to CNC it later on and want to use steppers to drive it I would consider building the mechanics into the machine now and housing a control box that will ultimately have enough room for all of your drives and power supply needs. When I've done this type of thing [professionally but not with machine tools] I lay out the panel and drill it for the extra drives and wire them in ahead of time using the one drive that we bought as a template. Judging from your restoration work you seem methodical but I dont know how well you are with electronics.

                      So now you have a control box that can accept your Mach3 parallel port input for 2-3 axes that is mounted to your machine and wired to your one stepper. All you need now is a box that will output the step and direction signals to the parallel port as an intermediate stepping stone until you get your PC running.

                      You can use a microcontroller to do this easily and I'd recommend an Arduino since they come with free software and are USB programmable. There is huge community support as well. Write a program that takes in a Potentiometer input via analog and converts it to a scaled pulse train, and then gate that with a "Fwd-OFF-Reverse" switch and you are done. You could do it with a 555 timer and some logic gates too, but I'd only do that if you are more into electronics than programming. I'd do the microcontroller myself but I like to program in C/C++.

                      I need to do a power feed on my lathe and this might be a good solution for that until I CNC the beast.

                      KEJR

                      Comment

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