Question about crooked star and & disk cal results

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  • Question about crooked star and & disk cal results

    Ive been searching around for the forum for this, and ive found alot of threads about calibration, but nothing really that answers my question.

    I have a disk thats 10mm in diameter. I calibrate it and it seems to measure the sphere fine and i get good STD values(around 0.002).
    But the diameter of the disk is usually around 10.015 - 10.02, where as all the other ruby balls are usually abit under the nom. diameter, (which i read it should be). But should the disks diameter be bigger than the nominal or is it fine as long as the STD is good?

    Another question about star probes: I have a star probe with 3: 1mm tips. from A0B0 perspective they're pointing west, north, and east. The star got loose one day from the stem, so we had to screw it back in. Now its a little bit angled, so that ex. the north tip that nominally points 0.1.0, in reality points 0,001. 0,92. 0.

    So when i calibrate this star i get good STD, but bad diameters, and they all vary depending on the angle. Nom is 1mm, and i get all from 0.997 to 0.970. Will this be a problem for my measurment or should i try to straighten out the star tip more or buy a new one?

  • #2
    For the disc stylus, what probe, module, extension length are you using? Also what is the thickness of the disc and what angles have you set for qualification in the Measure Probe settings.

    For the star probe, you would be best getting them as square as possible. You could also try using a start angle of 10 in your Measure Probe settings to avoid the tip shanking.


    • pcdmisstudent
      pcdmisstudent commented
      Editing a comment
      Disc style is diameter 10mm, thickness 1.2, (had to custom make this in probe.dat) + extension 50mm . Start angle -4.8 to 4.8, 3 levels.

      And regarding star probe: how would i get it square? Just eyeball it?
      Start angle is already at 15 degrees so no shank hits occur

    • WM321
      WM321 commented
      Editing a comment
      Personally I just eyeball it, screw in the bottom piece lightly and leave the star offset slightly, then when you tighten it with the tools, the star section should move slightly counter clockwise. usually takes a couple of goes.

  • #3
    if i remember correctly the angle for disk should be 7 deg


    • gibsonridge
      gibsonridge commented
      Editing a comment
      my bad, (mondays!!) yes it does depend on thickness. , there is a formula out there / i just don't have it on hand right now

    • Cumofo
      Cumofo commented
      Editing a comment

    • pcdmisstudent
      pcdmisstudent commented
      Editing a comment
      Cumofo That youtube link is blocked in my country
      gibsonridge nps i have the formula on hand if you wanted it:
      18mm disc dia x 2mm thick
      Calibrate using only 70% of the disk thickness (out of square comp.)

      2mm x .70 = 1.4mm

      half of 70% thickness
      1.4mm / 2 = .7mm
      Half probe dia.
      Calculate the angle from horizontal center line to half disk thickness

      SineA= .7/9

      Start angle -4.4º
      End angle 4.4º

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