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IndustryArena Forum > Tools / Tooling Technology > Calibration / Measurement > Chinese pancake-style make/break Z-height setter detector: how's it work? [Picture]
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  1. #1
    Join Date
    Jul 2003

    Chinese pancake-style make/break Z-height setter detector: how's it work? [Picture]

    These were all the rage a few years ago when this one was shipped with my machine. Now they're not showing up as ubiquitously in searches.

    I've used mine less than a hundred times, but it has started complaining that it's "already triggered" when a probe commences.

    I've had it apart, and it's so simple it's too hard to understand, if you get what I mean. An aluminum base (anodized?) sitting on an insulator, with a brass plunger sitting on a steel spring resting in a hollow in the base.

    It has to be a mere continuity switch (make or break), but it seems to be metal on metal at all points along the length of travel.

    If I'm right, in normal working operation, it presents a dead short (0V) to the control board until tool contact breaks the connection and a high results.

    I've seen criticisms of the design complaining that the anodized nature of the aluminum (esp. the colored versions) results in poor conductivity and recommendations for improving it involve scraping to bare metal and securing a copper wire.

    I am curious if the design of the piece "relies" on the anodized nature of some pieces at some points to insulate, and if so, whether wear-and-tear will ultimately remove it.

    Can anyone explain?

    Thank you.
    CNZ Cane
    Incidentally those crash marks in the top may not have been my fault after all, if the design of the thing every so often permits contact to go undetected.

  2. #2
    Join Date
    Jul 2003

    Re: Chinese pancake-style make/break Z-height setter detector: how's it work? [Pictur

    SOLVED. Short answer: It is NOT a "switch"--of any kind. It is the electrical equivalent of a lump of metal, connected to electrical ground.

    While it does have "moving parts," they have everything to do with absorbing impact of the cutting tool without, normally, defacing the top surface of the brass plunger (or harming the cutting edge). The moving parts have nothing to do, whatsoever, with electrical "switching." In fact, while all of the metal parts, probably do stay in contact with each other mechanically throughout the full motion of the plunger (and thus electrically in contact as well), the ONLY moment when the plunger, and the spring, and the base must be in electrical contact, is at the Instantaneous Moment the cutting tool contacts the plunger.

    At that moment, the G38 (probe) code becomes aware that contact has been made, notes it, and retracts. The spring is designed to compensate for momentum which might carry the tool further down during the time the controller is deciding contact has been made.

    IF, otoh, the electrical connection between plunger, spring, and base is so poor that tool contact is not detected--the spring-loaded travel MIGHT still protect tool-edge and detector IF G38 has been coded properly to limit maximum travel to less than what the detector can take.

    The explanation for my particular detector's mistaken report that it is already triggered, is that the controller has detected that the tool is already in contact with the plunger. The explanation for how that might be happening is what escapes me, and led me down the rabbit hole of hunting for a non-existent "internal switch" in the detector. "Plunger not returning to top of stroke," "plunger not making good connection to base," do not explain why the controller believes the tool is already in contact with the sufrace when a G38 probe command is issued.

    As reward for you patience with my trivial ramblings, I offer you these "inside views" of the tool. (Note the machine screw in the bottom center of the detector is to assist the plunger spring to stay "relatively centered" in the base, and thus set relatively flat on its end, instead of wandering off to one edge and sitting on tangent "point" contacts. And incidentally, I coated top and bottom of spring with dielectric grease before re-assembling: do not coat the outside of the plunger with the stuff or you will learn that the combination of viscosity and cool temperatures can prevent the plunger from returning.)

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