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Re: Mini Mill CNC Conversion Recommendation for limit switches

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  • 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 1 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 2 of 10 , Apr 7, 2013
      • 0 Attachment
        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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