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Mini Mill CNC Conversion Recommendation for limit switches

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  • Matt
    I ve finished up the bulk of my Mini Mill converversion to CNC and now I m working on the electrical part. (Wiring up the controller, motors, etc.) One area
    Message 1 of 10 , Apr 4, 2013
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      I've finished up the bulk of my Mini Mill converversion to CNC and now I'm working on the electrical part. (Wiring up the controller, motors, etc.) One area that I haven't figured out is what kind of limit switches to install. I've searched the forum and Google and I've read up on several options. Some using micro-switches, small switches with magnets and the like.

      I'm interested in a solution that will be pretty consistent for homing the machine. I've read in some places where people were using optical sensors but I haven't seen any specific part recommendations (mfg, model, etc.)

      I was hoping that if folks had some recommendations / experiences in setting this up they'd be willing to share.
    • Malcolm Parker-Lisberg
      Matt Microswitches work fine for most uses and are relatively free from on external influences such as dust or magnetic fields, unless you want to re-position
      Message 2 of 10 , Apr 5, 2013
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        Matt

        Microswitches work fine for most uses and are relatively free from on external influences such as dust or magnetic fields, unless you want to re-position a part to rework it. The fact that the reference point has shifted by a few tho' has no effect on a fresh CNC run. Slotted optical sensors are available from Mouser etc or even a dead serial Mouse. I have seen a design on the web that uses a spring loaded plunger with a hanging flag that enters the slotted sensor. Homing switches are more important than limit switches for determining the reference position and the precision of the Home also depends on how good the CNC software is at detecting it. LinuxCNC has three homing switch approach options.

        Malcolm

        I don't suffer from insanity I enjoy it!
        Mene, mene, tekel, upharsin
        The writing is on the wall.

        --- On Fri, 4/5/13, Matt <matt@...> wrote:

        From: Matt <matt@...>
        Subject: [GrizHFMinimill] Mini Mill CNC Conversion Recommendation for limit switches
        To: GrizHFMinimill@yahoogroups.com
        Date: Friday, April 5, 2013, 2:37 AM

         

        I've finished up the bulk of my Mini Mill converversion to CNC and now I'm working on the electrical part. (Wiring up the controller, motors, etc.) One area that I haven't figured out is what kind of limit switches to install. I've searched the forum and Google and I've read up on several options. Some using micro-switches, small switches with magnets and the like.

        I'm interested in a solution that will be pretty consistent for homing the machine. I've read in some places where people were using optical sensors but I haven't seen any specific part recommendations (mfg, model, etc.)

        I was hoping that if folks had some recommendations / experiences in setting this up they'd be willing to share.

      • Ebner Heating & Cooling Company
        I m really curious as to what electronics & software would be needed to convert a X2 to CNC operation. Is there any material that a guy can read to familiarize
        Message 3 of 10 , Apr 5, 2013
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          I'm really curious as to what electronics & software would be needed to convert a X2 to CNC operation. Is there any material that a guy can read to familiarize himself with the components needed and procedures that he will need to follow? I like to do the homework before jumping in with both feet and I hate purchasing something that won't work as intended.

           

          Thanks Mike

           

          Matt

          Microswitches work fine for most uses and are relatively free from on external influences such as dust or magnetic fields, unless you want to re-position a part to rework it. The fact that the reference point has shifted by a few tho' has no effect on a fresh CNC run. Slotted optical sensors are available from Mouser etc or even a dead serial Mouse. I have seen a design on the web that uses a spring loaded plunger with a hanging flag that enters the slotted sensor. Homing switches are more important than limit switches for determining the reference position and the precision of the Home also depends on how good the CNC software is at detecting it. LinuxCNC has three homing switch approach options.

          Malcolm

          I don't suffer from insanity I enjoy it!
          Mene, mene, tekel, upharsin
          The writing is on the wall.

          --- On Fri, 4/5/13, Matt wrote:

          From: Matt
          Subject: [GrizHFMinimill] Mini Mill CNC Conversion Recommendation for limit switches
          To: GrizHFMinimill@yahoogroups.com
          Date: Friday, April 5, 2013, 2:37 AM

          I've finished up the bulk of my Mini Mill converversion to CNC and now I'm working on the electrical part. (Wiring up the controller, motors, etc.) One area that I haven't figured out is what kind of limit switches to install. I've searched the forum and Google and I've read up on several options. Some using micro-switches, small switches with magnets and the like.

          I'm interested in a solution that will be pretty consistent for homing the machine. I've read in some places where people were using optical sensors but I haven't seen any specific part recommendations (mfg, model, etc.)

          I was hoping that if folks had some recommendations / experiences in setting this up they'd be willing to share.
           

           



          Thanks
          Mike Ebner

        • Harvey White
          ... I ve used microswitches and optical sensors. Of the two, the microswitch is a bit easier to wire, but not absolutely as accurate. The optical sensor is
          Message 4 of 10 , Apr 5, 2013
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            On Fri, 05 Apr 2013 01:37:59 -0000, you wrote:

            >I've finished up the bulk of my Mini Mill converversion to CNC and now I'm working on the electrical part. (Wiring up the controller, motors, etc.) One area that I haven't figured out is what kind of limit switches to install. I've searched the forum and Google and I've read up on several options. Some using micro-switches, small switches with magnets and the like.
            >
            >I'm interested in a solution that will be pretty consistent for homing the machine. I've read in some places where people were using optical sensors but I haven't seen any specific part recommendations (mfg, model, etc.)
            >
            >I was hoping that if folks had some recommendations / experiences in setting this up they'd be willing to share.

            I've used microswitches and optical sensors. Of the two, the
            microswitch is a bit easier to wire, but not absolutely as accurate.
            The optical sensor is mounted on a small homemade PC board (you can
            get the kind with wires if you want). A small flag interrupts the
            light beam. Non contact and pretty accurate and repeatable.

            http://www.digikey.com/product-detail/en/RPI-441C1/511-1341-ND/714719

            is a suitable part, and will not break the bank. Note that you will
            need two resistors (there's hookup information in the data sheet). I
            rather arbitrarily picked one that they had a lot of, and the price
            was under a dollar.

            Harvey
          • Malcolm Parker-Lisberg
            Mike You need: A PC with a parallel printer port to run the software, for FREE  LinuxCNC (EMC2) download the software and burn a disc.
            Message 5 of 10 , Apr 5, 2013
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              Mike

              You need:
              A PC with a parallel printer port to run the software, for FREE  LinuxCNC (EMC2) download the software and burn a disc.

              <http://www.linuxcnc.org/index.php/download>
              Run the latency test,
              <http://www.linuxcnc.org/docs/LinuxCNC_Getting_Started.pdf>
              You need about 12,000 nS and enough memory to have a good machine.
              I had problems, turned out to be the video board, reverted to the bog standard board and got 11,000 nS
              You then need a 'Break out board' Stepper driver boards, stepper motors and power supplies.
              I use a 24V 15A switching supply with an additional large capacitor and 5V supply from Hong Kong ($25 and $5) to drive 1.8Nm stepper motors.
              There is a new stepper driver, looks good, see:
              <http://www.ebay.co.uk/itm/181085195528?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649>
              This is a replacement for the TB6560 which has caused some people problems (not me)
              See:
              <http://www.ebay.co.uk/sch/cnc-parts4u/m.html?_nkw=&_armrs=1&_from=&_ipg=&_trksid=p3686> for a lot of my needs, but he is UK based. Breakout boards are available from many sources.
              The main hardware requirement is for antibacklash feed screws, of which the more yoy spend the higher the spec. Acme screws with plastic nuts work fine for most low cost requirements. Direct stepper drive or timing belt drive depends upon the table loading, if you are cutting steel, use timing pulley reduction drive to the feedscrews.

              That is just one option, Mach3 is commonly used software, but you have to pay to be able to use larger files than can be used in the demo version.

              I will not enter the LinuxCNC, Mach3 turf war..

              Malcolm



              I don't suffer from insanity I enjoy it!
              Mene, mene, tekel, upharsin
              The writing is on the wall.

              --- On Fri, 4/5/13, Ebner Heating & Cooling Company <mike@...> wrote:

              From: Ebner Heating & Cooling Company <mike@...>
              Subject: Re: [GrizHFMinimill] Mini Mill CNC Conversion Recommendation for limit switches
              To: GrizHFMinimill@yahoogroups.com
              Date: Friday, April 5, 2013, 12:54 PM

               

              I'm really curious as to what electronics & software would be needed to convert a X2 to CNC operation. Is there any material that a guy can read to familiarize himself with the components needed and procedures that he will need to follow? I like to do the homework before jumping in with both feet and I hate purchasing something that won't work as intended.

               

              Thanks Mike

               

              Matt

              Microswitches work fine for most uses and are relatively free from on external influences such as dust or magnetic fields, unless you want to re-position a part to rework it. The fact that the reference point has shifted by a few tho' has no effect on a fresh CNC run. Slotted optical sensors are available from Mouser etc or even a dead serial Mouse. I have seen a design on the web that uses a spring loaded plunger with a hanging flag that enters the slotted sensor. Homing switches are more important than limit switches for determining the reference position and the precision of the Home also depends on how good the CNC software is at detecting it. LinuxCNC has three homing switch approach options.

              Malcolm

              I don't suffer from insanity I enjoy it!
              Mene, mene, tekel, upharsin
              The writing is on the wall.

              --- On Fri, 4/5/13, Matt wrote:

              From: Matt
              Subject: [GrizHFMinimill] Mini Mill CNC Conversion Recommendation for limit switches
              To: GrizHFMinimill@yahoogroups.com
              Date: Friday, April 5, 2013, 2:37 AM

              I've finished up the bulk of my Mini Mill converversion to CNC and now I'm working on the electrical part. (Wiring up the controller, motors, etc.) One area that I haven't figured out is what kind of limit switches to install. I've searched the forum and Google and I've read up on several options. Some using micro-switches, small switches with magnets and the like.

              I'm interested in a solution that will be pretty consistent for homing the machine. I've read in some places where people were using optical sensors but I haven't seen any specific part recommendations (mfg, model, etc.)

              I was hoping that if folks had some recommendations / experiences in setting this up they'd be willing to share.
               

               



              Thanks
              Mike Ebner

            • Matt
              Thanks for the input. I m going to put on my lab coat and try a set of magnetic switches using the SS441A and optos from Optek OPB930W51Z and see which works
              Message 6 of 10 , Apr 5, 2013
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                Thanks for the input. I'm going to put on my lab coat and try a set of magnetic switches using the SS441A and optos from Optek OPB930W51Z and see which works better. It will be a week before the parts arrive but I'll post what I find.

                One other question I had, can't the limit switches also be used for homing? I've seen people distinguish between the two but a limit switch can be the same as a home, no ?

                --- In GrizHFMinimill@yahoogroups.com, "Ebner Heating & Cooling Company" <mike@...> wrote:
                >
                >
                >
                >
                > I'm really curious as to what electronics
                > & software would be needed to convert a X2 to CNC operation. Is there
                > any material that a guy can read to familiarize himself with the
                > components needed and procedures that he will need to follow? I like to do
                > the homework before jumping in with both feet and I hate purchasing
                > something that won't work as intended.
                >  
                > Thanks Mike
                >
                >
                >
                >
                >
                >  
                >
                >
                >
                >
                > Matt
                >
                >
                >
                > Microswitches work fine for most uses and are relatively free from
                > on external influences such as dust or magnetic fields, unless you
                > want to re-position a part to rework it. The fact that the
                > reference point has shifted by a few tho' has no effect on a fresh
                > CNC run. Slotted optical sensors are available from Mouser etc or
                > even a dead serial Mouse. I have seen a design on the web that
                > uses a spring loaded plunger with a hanging flag that enters the
                > slotted sensor. Homing switches are more important than limit
                > switches for determining the reference position and the precision
                > of the Home also depends on how good the CNC software is at
                > detecting it. LinuxCNC has three homing switch approach
                > options.
                >
                >
                >
                > Malcolm
                >
                >
                >
                > I don't suffer from insanity I enjoy it!
                >
                > Mene, mene, tekel, upharsin
                >
                > The writing is on the wall.
                >
                >
                >
                > --- On Fri, 4/5/13, Matt wrote:
                >
                >
                >
                >
                > From: Matt
                >
                > Subject: [GrizHFMinimill] Mini Mill CNC Conversion Recommendation
                > for limit switches
                >
                > To: GrizHFMinimill@yahoogroups.com
                >
                > Date: Friday, April 5, 2013, 2:37 AM
                >
                >
                >
                >
                >
                >
                >
                > I've finished up the bulk of my Mini Mill converversion to
                > CNC and now I'm working on the electrical part. (Wiring up the
                > controller, motors, etc.) One area that I haven't figured out
                > is what kind of limit switches to install. I've searched the
                > forum and Google and I've read up on several options. Some
                > using micro-switches, small switches with magnets and the
                > like.
                >
                >
                >
                > I'm interested in a solution that will be pretty consistent
                > for homing the machine. I've read in some places where people
                > were using optical sensors but I haven't seen any specific
                > part recommendations (mfg, model, etc.)
                >
                >
                >
                > I was hoping that if folks had some recommendations /
                > experiences in setting this up they'd be willing to share.
                >
                >  
                >
                >
                >
                >
                >
                >
                >
                >
                >  
                >
                >
                > <style type="text/css">
                > -></style>
                >
                >
                >
                >
                >
                > Thanks
                >
                > Mike Ebner
                >
              • Barry Young
                When I did my minimill conversion I chose Cherry brand roller equipped micro switches, but for you I would recommend these  from Parts Express Model Number
                Message 7 of 10 , Apr 6, 2013
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                  When I did my minimill conversion I chose Cherry brand roller equipped micro switches, but for you I would recommend these 

                  from Parts Express Model Number 66-4002

                   
                  060-606 : SPDT Snap-Action Standard Micro Switch with Roller Lever

                  Roll over image to zoom
                  060-606
                   

                  SPDT Snap-Action Standard Micro Switch with Roller Lever

                  Brand: Parts Express   |   Model: 66-4002


                  Reviews

                  Product Q&A


                  Overview
                  Standard micro switch. Specifications: • Current rating: 10A @ 125 VAC and 250 VAC • Housing dimensions: 28.8 mm L x 15.8 mm W x 10.3 mm D • Contacts: 3 • Approval: UL.
                  Part #:  060-606     Weight:  0.01 lbs.  


                  cause they are way way cheaper. 

                  Barry

                  From: Matt <matt@...>
                  To: GrizHFMinimill@yahoogroups.com
                  Sent: Thursday, April 4, 2013 6:37 PM
                  Subject: [GrizHFMinimill] Mini Mill CNC Conversion Recommendation for limit switches

                  I've finished up the bulk of my Mini Mill converversion to CNC and now I'm working on the electrical part.  (Wiring up the controller, motors, etc.) One area that I haven't figured out is what kind of limit switches to install.  I've searched the forum and Google and I've read up on several options.  Some using micro-switches, small switches with magnets and the like. 

                  I'm interested in a solution that will be pretty consistent for homing the machine.  I've read in some places where people were using optical sensors but I haven't seen any specific part recommendations (mfg, model, etc.)

                  I was hoping that if folks had some recommendations  / experiences in setting this up they'd be willing to share.



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                • Harvey White
                  ... The limit switches can be used as homing switches. Typically, with separate limit and home switches, the home switches are within the limit switches and
                  Message 8 of 10 , Apr 6, 2013
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                    On Sat, 06 Apr 2013 02:38:58 -0000, you wrote:

                    >Thanks for the input. I'm going to put on my lab coat and try a set of magnetic switches using the SS441A and optos from Optek OPB930W51Z and see which works better. It will be a week before the parts arrive but I'll post what I find.
                    >
                    >One other question I had, can't the limit switches also be used for homing? I've seen people distinguish between the two but a limit switch can be the same as a home, no ?

                    The limit switches can be used as homing switches.

                    Typically, with separate limit and home switches, the home switches
                    are "within" the limit switches and at one end of the travel.

                    In some installations, limit switches (IIRC) are wired in series and
                    are normally closed. Any limit stops the machine, it's up to you to
                    figure out where you were when you were doing that.

                    Home switches have an individual connection and are typically normally
                    open.

                    You can be in X home and then seek (validly) Y home and then Z home.

                    Some of the CNC packages (I cannot speak for all) such as Turbo CNC
                    allow (again, IIRC, been a while) the limit switch on one axis to be
                    the home switch for the same axis. It's a software setup.


                    Harvey

                    >
                    >--- In GrizHFMinimill@yahoogroups.com, "Ebner Heating & Cooling Company" <mike@...> wrote:
                    >>
                    >>
                    >>
                    >>
                    >> I'm really curious as to what electronics
                    >> & software would be needed to convert a X2 to CNC operation. Is there
                    >> any material that a guy can read to familiarize himself with the
                    >> components needed and procedures that he will need to follow? I like to do
                    >> the homework before jumping in with both feet and I hate purchasing
                    >> something that won't work as intended.
                    >>  
                    >> Thanks Mike
                    >>
                    >>
                    >>
                    >>
                    >>
                    >>  
                    >>
                    >>
                    >>
                    >>
                    >> Matt
                    >>
                    >>
                    >>
                    >> Microswitches work fine for most uses and are relatively free from
                    >> on external influences such as dust or magnetic fields, unless you
                    >> want to re-position a part to rework it. The fact that the
                    >> reference point has shifted by a few tho' has no effect on a fresh
                    >> CNC run. Slotted optical sensors are available from Mouser etc or
                    >> even a dead serial Mouse. I have seen a design on the web that
                    >> uses a spring loaded plunger with a hanging flag that enters the
                    >> slotted sensor. Homing switches are more important than limit
                    >> switches for determining the reference position and the precision
                    >> of the Home also depends on how good the CNC software is at
                    >> detecting it. LinuxCNC has three homing switch approach
                    >> options.
                    >>
                    >>
                    >>
                    >> Malcolm
                    >>
                    >>
                    >>
                    >> I don't suffer from insanity I enjoy it!
                    >>
                    >> Mene, mene, tekel, upharsin
                    >>
                    >> The writing is on the wall.
                    >>
                    >>
                    >>
                    >> --- On Fri, 4/5/13, Matt wrote:
                    >>
                    >>
                    >>
                    >>
                    >> From: Matt
                    >>
                    >> Subject: [GrizHFMinimill] Mini Mill CNC Conversion Recommendation
                    >> for limit switches
                    >>
                    >> To: GrizHFMinimill@yahoogroups.com
                    >>
                    >> Date: Friday, April 5, 2013, 2:37 AM
                    >>
                    >>
                    >>
                    >>
                    >>
                    >>
                    >>
                    >> I've finished up the bulk of my Mini Mill converversion to
                    >> CNC and now I'm working on the electrical part. (Wiring up the
                    >> controller, motors, etc.) One area that I haven't figured out
                    >> is what kind of limit switches to install. I've searched the
                    >> forum and Google and I've read up on several options. Some
                    >> using micro-switches, small switches with magnets and the
                    >> like.
                    >>
                    >>
                    >>
                    >> I'm interested in a solution that will be pretty consistent
                    >> for homing the machine. I've read in some places where people
                    >> were using optical sensors but I haven't seen any specific
                    >> part recommendations (mfg, model, etc.)
                    >>
                    >>
                    >>
                    >> I was hoping that if folks had some recommendations /
                    >> experiences in setting this up they'd be willing to share.
                    >>
                    >>  
                    >>
                    >>
                    >>
                    >>
                    >>
                    >>
                    >>
                    >>
                    >>  
                    >>
                    >>
                    >> <style type="text/css">
                    >> -></style>
                    >>
                    >>
                    >>
                    >>
                    >>
                    >> Thanks
                    >>
                    >> Mike Ebner
                    >>
                    >
                  • oldstudentmsgt
                    Matt, my experience is in satellite systems, aircraft, and such, not mini-lathes and mills, but a limit switch is intended to prevent you from hitting a
                    Message 9 of 10 , Apr 7, 2013
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                      Matt, my experience is in satellite systems, aircraft, and such, not mini-lathes and mills, but a limit switch is intended to prevent you from hitting a mechanical limit, and damaging the machinery. One of the satellite vans I worked on, the AN/MSC-46, was originally designed to track non-synchronous satellites. Even modified for synchronous satellites, as it was when I worked on it, that 40' dish could MOVE! Hitting a mechanical stop would have thrown the dish, and its multi-ton counterweight, right across our satellite site. BAD IDEA! ;)

                      Not quite so much of a problem with a small mill or lathe, but broken gears and such are still a PITA.

                      Switches are relatively cheap. I'd have a homing switch AND a limit switch far enough from the mechanical limits to prevent such crashes were I the one doing the building.

                      Even on a tight budget, like I'm on. ;)

                      Bill in OKC


                      --- In GrizHFMinimill@yahoogroups.com, "Matt" <matt@...> wrote:
                      >
                      > Thanks for the input. I'm going to put on my lab coat and try a set of magnetic switches using the SS441A and optos from Optek OPB930W51Z and see which works better. It will be a week before the parts arrive but I'll post what I find.
                      >
                      > One other question I had, can't the limit switches also be used for homing? I've seen people distinguish between the two but a limit switch can be the same as a home, no ?
                      >
                      > --- In GrizHFMinimill@yahoogroups.com, "Ebner Heating & Cooling Company" <mike@> wrote:
                      > >
                      > >
                      > >
                      > >
                      > > I'm really curious as to what electronics
                      > > & software would be needed to convert a X2 to CNC operation. Is there
                      > > any material that a guy can read to familiarize himself with the
                      > > components needed and procedures that he will need to follow? I like to do
                      > > the homework before jumping in with both feet and I hate purchasing
                      > > something that won't work as intended.
                      > >  
                      > > Thanks Mike
                      > >
                      > >
                      > >
                      > >
                      > >
                      > >  
                      > >
                      > >
                      > >
                      > >
                      > > Matt
                      > >
                      > >
                      > >
                      > > Microswitches work fine for most uses and are relatively free from
                      > > on external influences such as dust or magnetic fields, unless you
                      > > want to re-position a part to rework it. The fact that the
                      > > reference point has shifted by a few tho' has no effect on a fresh
                      > > CNC run. Slotted optical sensors are available from Mouser etc or
                      > > even a dead serial Mouse. I have seen a design on the web that
                      > > uses a spring loaded plunger with a hanging flag that enters the
                      > > slotted sensor. Homing switches are more important than limit
                      > > switches for determining the reference position and the precision
                      > > of the Home also depends on how good the CNC software is at
                      > > detecting it. LinuxCNC has three homing switch approach
                      > > options.
                      > >
                      > >
                      > >
                      > > Malcolm
                      > >
                      > >
                      > >
                      > > I don't suffer from insanity I enjoy it!
                      > >
                      > > Mene, mene, tekel, upharsin
                      > >
                      > > The writing is on the wall.
                      > >
                      > >
                      > >
                      > > --- On Fri, 4/5/13, Matt wrote:
                      > >
                      > >
                      > >
                      > >
                      > > From: Matt
                      > >
                      > > Subject: [GrizHFMinimill] Mini Mill CNC Conversion Recommendation
                      > > for limit switches
                      > >
                      > > To: GrizHFMinimill@yahoogroups.com
                      > >
                      > > Date: Friday, April 5, 2013, 2:37 AM
                      > >
                      > >
                      > >
                      > >
                      > >
                      > >
                      > >
                      > > I've finished up the bulk of my Mini Mill converversion to
                      > > CNC and now I'm working on the electrical part. (Wiring up the
                      > > controller, motors, etc.) One area that I haven't figured out
                      > > is what kind of limit switches to install. I've searched the
                      > > forum and Google and I've read up on several options. Some
                      > > using micro-switches, small switches with magnets and the
                      > > like.
                      > >
                      > >
                      > >
                      > > I'm interested in a solution that will be pretty consistent
                      > > for homing the machine. I've read in some places where people
                      > > were using optical sensors but I haven't seen any specific
                      > > part recommendations (mfg, model, etc.)
                      > >
                      > >
                      > >
                      > > I was hoping that if folks had some recommendations /
                      > > experiences in setting this up they'd be willing to share.
                      > >
                      > >  
                      > >
                      > >
                      > >
                      > >
                      > >
                      > >
                      > >
                      > >
                      > >  
                      > >
                      > >
                      > > <style type="text/css">
                      > > -></style>
                      > >
                      > >
                      > >
                      > >
                      > >
                      > > Thanks
                      > >
                      > > Mike Ebner
                      > >
                      >
                    • trainliker
                      A limit switch and a homing switch can most certainly be the same switch so long as the home osition is reasonably outside of the operating range. It simply
                      Message 10 of 10 , Apr 7, 2013
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                        A limit switch and a homing switch can most certainly be the same switch so long as the home osition is reasonably outside of the operating range.  It simply saves a switch and it is common to see a single switch tied to both the home and a limit input of a servo controller.  Not doing this merely needlessly adds another switch (and with each item added, system reliability is reduced.)
                         
                        In some systems, if you hit a limit switch, the controller will still allow movement in the direction away from the tripped limit to get back into the safe operating zone.  after movement back into the operating zone, then you can move again in either direction.
                         
                        Some systems also have overtravel switches in addition to limit switches.  This may seem like a "distinction without a difference" (as a lawyer might say) but the over travel switches can be even further out than the limit switches meaning you have something very serious going on.  If an overtravel event occurs, there is typically no recovery and the system will no longer run and require user attention as opposed to a limit switch where it might be automatically possible to move back into the operating range.
                         
                        Chuck K. 
                         
                         
                        ----- Original Message -----
                        Sent: Sunday, April 07, 2013 9:46 AM
                        Subject: [GrizHFMinimill] Re: Mini Mill CNC Conversion Recommendation for limit switches

                         

                        Matt, my experience is in satellite systems, aircraft, and such, not mini-lathes and mills, but a limit switch is intended to prevent you from hitting a mechanical limit, and damaging the machinery. One of the satellite vans I worked on, the AN/MSC-46, was originally designed to track non-synchronous satellites. Even modified for synchronous satellites, as it was when I worked on it, that 40' dish could MOVE! Hitting a mechanical stop would have thrown the dish, and its multi-ton counterweight, right across our satellite site. BAD IDEA! ;)

                        Not quite so much of a problem with a small mill or lathe, but broken gears and such are still a PITA.

                        Switches are relatively cheap. I'd have a homing switch AND a limit switch far enough from the mechanical limits to prevent such crashes were I the one doing the building.

                        Even on a tight budget, like I'm on. ;)

                        Bill in OKC

                        --- In GrizHFMinimill@yahoogroups.com, "Matt" <matt@...> wrote:
                        >
                        > Thanks for the input. I'm going to put on my lab coat and try a set of magnetic switches using the SS441A and optos from Optek OPB930W51Z and see which works better. It will be a week before the parts arrive but I'll post what I find.
                        >
                        > One other question I had, can't the limit switches also be used for homing? I've seen people distinguish between the two but a limit switch can be the same as a home, no ?
                        >
                        > --- In GrizHFMinimill@yahoogroups.com, "Ebner Heating & Cooling Company" <mike@> wrote:
                        > >
                        > >
                        > >
                        > >
                        > > I'm really curious as to what electronics
                        > > & software would be needed to convert a X2 to CNC operation. Is there
                        > > any material that a guy can read to familiarize himself with the
                        > > components needed and procedures that he will need to follow? I like to do
                        > > the homework before jumping in with both feet and I hate purchasing
                        > > something that won't work as intended.
                        > >  
                        > > Thanks Mike
                        > >
                        > >
                        > >
                        > >
                        > >
                        > >  
                        > >
                        > >
                        > >
                        > >
                        > > Matt
                        > >
                        > >
                        > >
                        > > Microswitches work fine for most uses and are relatively free from
                        > > on external influences such as dust or magnetic fields, unless you
                        > > want to re-position a part to rework it. The fact that the
                        > > reference point has shifted by a few tho' has no effect on a fresh
                        > > CNC run. Slotted optical sensors are available from Mouser etc or
                        > > even a dead serial Mouse. I have seen a design on the web that
                        > > uses a spring loaded plunger with a hanging flag that enters the
                        > > slotted sensor. Homing switches are more important than limit
                        > > switches for determining the reference position and the precision
                        > > of the Home also depends on how good the CNC software is at
                        > > detecting it. LinuxCNC has three homing switch approach
                        > > options.
                        > >
                        > >
                        > >
                        > > Malcolm
                        > >
                        > >
                        > >
                        > > I don't suffer from insanity I enjoy it!
                        > >
                        > > Mene, mene, tekel, upharsin
                        > >
                        > > The writing is on the wall.
                        > >
                        > >
                        > >
                        > > --- On Fri, 4/5/13, Matt wrote:
                        > >
                        > >
                        > >
                        > >
                        > > From: Matt
                        > >
                        > > Subject: [GrizHFMinimill] Mini Mill CNC Conversion Recommendation
                        > > for limit switches
                        > >
                        > > To: GrizHFMinimill@yahoogroups.com
                        > >
                        > > Date: Friday, April 5, 2013, 2:37 AM
                        > >
                        > >
                        > >
                        > >
                        > >
                        > >
                        > >
                        > > I've finished up the bulk of my Mini Mill converversion to
                        > > CNC and now I'm working on the electrical part. (Wiring up the
                        > > controller, motors, etc.) One area that I haven't figured out
                        > > is what kind of limit switches to install. I've searched the
                        > > forum and Google and I've read up on several options. Some
                        > > using micro-switches, small switches with magnets and the
                        > > like.
                        > >
                        > >
                        > >
                        > > I'm interested in a solution that will be pretty consistent
                        > > for homing the machine. I've read in some places where people
                        > > were using optical sensors but I haven't seen any specific
                        > > part recommendations (mfg, model, etc.)
                        > >
                        > >
                        > >
                        > > I was hoping that if folks had some recommendations /
                        > > experiences in setting this up they'd be willing to share.
                        > >
                        > >  
                        > >
                        > >
                        > >
                        > >
                        > >
                        > >
                        > >
                        > >
                        > >  
                        > >
                        > >
                        > > <style type="text/css">
                        > > -></style>
                        > >
                        > >
                        > >
                        > >
                        > >
                        > > Thanks
                        > >
                        > > Mike Ebner
                        > >
                        >

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