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Re: [diy_3d_printing_and_fabrication] Digest Number 398

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  • Roger Hamlett
    ... Yes, I d begun to suspect this was the case. So you actually need not just removal of pressure, but positive _subtraction_ at the tip, to prevent ooze.
    Message 1 of 3 , Feb 2, 2011
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      > Heterogeneous fluids (as in suspensions and pastes) are usually
      > non-Newtonian fluids so there will be a certain "elastic" tendency.
      > Pneumatic control must be quite a difficult design to implement. In any
      > case I would rather use oil pressure rather than air to actuate it.
      > Screw drive plungers are more reliable and solid, also quicker to revert
      > direction.
      >
      > On Tue, 2011-02-01 at 07:56 -0500, Boman33 wrote:
      >
      Yes,
      I'd begun to suspect this was the case. So you actually need not just
      'removal' of pressure, but positive _subtraction_ at the tip, to prevent
      ooze.
      So if you have a 'pushed' syringe, feeding to a simple nozzle, with
      control of the feed, but then have a short length of pipe between the
      syringe and the nozzle, that is slightly squeezed at the side by an air
      piston, when the feed is on. Cut the feed, and at the same time, the
      feed piston stops pushing, the side pressure is relaxed (spring),
      actually creating a small suction at the nozzle, and 'pull back'.
      Not too complex, and seems to handle the likely problems.
      Have ordered some pipe, nozzles, and syringes, and going to play with this.

      Best Wishes
    • Boman33
      In principle it would work with the extra air plunger but I think you are unnecessarily making it more complex, creating several new variables and making it
      Message 2 of 3 , Feb 2, 2011
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        In principle it would work with the extra air plunger but I think you are
        unnecessarily making it more complex, creating several new variables and
        making it harder to control. For example, the flexible hose will flex and
        it will vary with temperature, consistency of the medium and so on. It will
        affect both the dispensing cycle and the off cycle.

        Why not just use the rigid syringe and plunger as I suggested. Today it is
        easy to get a backlash free linear actuator that in software can accurately
        be controlled and if needed also reversed.
        Bertho
        =============================

        From: Roger Hamlett Sent: Wednesday, February 02, 2011 11:50

        > Heterogeneous fluids (as in suspensions and pastes) are usually
        > non-Newtonian fluids so there will be a certain "elastic" tendency.
        > Pneumatic control must be quite a difficult design to implement. In any
        > case I would rather use oil pressure rather than air to actuate it.
        > Screw drive plungers are more reliable and solid, also quicker to revert
        > direction.
        >
        > On Tue, 2011-02-01 at 07:56 -0500, Boman33 wrote:
        >
        Yes,
        I'd begun to suspect this was the case. So you actually need not just
        'removal' of pressure, but positive _subtraction_ at the tip, to prevent
        ooze.
        So if you have a 'pushed' syringe, feeding to a simple nozzle, with
        control of the feed, but then have a short length of pipe between the
        syringe and the nozzle, that is slightly squeezed at the side by an air
        piston, when the feed is on. Cut the feed, and at the same time, the
        feed piston stops pushing, the side pressure is relaxed (spring),
        actually creating a small suction at the nozzle, and 'pull back'.
        Not too complex, and seems to handle the likely problems.
        Have ordered some pipe, nozzles, and syringes, and going to play with this.

        Best Wishes
      • Michael Couch
        All of this discussion seems to be the hard way when one considers the ease and accuracy of the projector forming a whole plane on each step. Why would you
        Message 3 of 3 , Feb 3, 2011
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          All of this discussion seems to be the hard way when one considers the ease and accuracy of the projector forming a whole plane on each step. Why would you still be working with this method?

          Michael Couch

          --- In diy_3d_printing_and_fabrication@yahoogroups.com, "Boman33" <boman33@...> wrote:
          >
          > In principle it would work with the extra air plunger but I think you are
          > unnecessarily making it more complex, creating several new variables and
          > making it harder to control. For example, the flexible hose will flex and
          > it will vary with temperature, consistency of the medium and so on. It will
          > affect both the dispensing cycle and the off cycle.
          >
          > Why not just use the rigid syringe and plunger as I suggested. Today it is
          > easy to get a backlash free linear actuator that in software can accurately
          > be controlled and if needed also reversed.
          > Bertho
          > =============================
          >
          > From: Roger Hamlett Sent: Wednesday, February 02, 2011 11:50
          >
          > > Heterogeneous fluids (as in suspensions and pastes) are usually
          > > non-Newtonian fluids so there will be a certain "elastic" tendency.
          > > Pneumatic control must be quite a difficult design to implement. In any
          > > case I would rather use oil pressure rather than air to actuate it.
          > > Screw drive plungers are more reliable and solid, also quicker to revert
          > > direction.
          > >
          > > On Tue, 2011-02-01 at 07:56 -0500, Boman33 wrote:
          > >
          > Yes,
          > I'd begun to suspect this was the case. So you actually need not just
          > 'removal' of pressure, but positive _subtraction_ at the tip, to prevent
          > ooze.
          > So if you have a 'pushed' syringe, feeding to a simple nozzle, with
          > control of the feed, but then have a short length of pipe between the
          > syringe and the nozzle, that is slightly squeezed at the side by an air
          > piston, when the feed is on. Cut the feed, and at the same time, the
          > feed piston stops pushing, the side pressure is relaxed (spring),
          > actually creating a small suction at the nozzle, and 'pull back'.
          > Not too complex, and seems to handle the likely problems.
          > Have ordered some pipe, nozzles, and syringes, and going to play with this.
          >
          > Best Wishes
          >
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