Check for hole, and sometimes find the depth.

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  • Check for hole, and sometimes find the depth.

    Hi Guys.

    I got involved in a minor project, where I been asked 2 questions:

    1) Can the CMM check if 2 holes are connected?

    Simply drive the probe into a hole, and if it doesn't touch anything go back til the clearplane.
    If it touches anything. Take the point, and return to clearplane.

    I would like the probe to return to clearplane no matter what happens.
    Sometimes we have some smaller burrs in the hole, that makes the program come to a hold, and I'd like to prevent that.



    2) How do I measure the depth of a drilled hole?

    Is there a easier way, other than this one:
    Measure the diameter, make an alignment in the center of that hole, and go down into the hole until it touches the bottom of the "cone".
    Calculate the offset to where the cylinder of the hole intersects the large diameter of the "cone".

    What if the angle of the drill changes from 118° to 140°, because the CNC-guys forgot to order the "original" one in time.
    And they only have to scan their tool to find the length.


    Oh, and by-the-way:
    How do I get PC-DMIS to drive the probe into a hole, and then lift it a bit up, before the diameter is measured?
    As the procedure is right now, it drives into the hole, and then go deeper for measuring the diameter.
    That's not right, I guess.


    Last edited by Mykel; 11-24-2020, 05:43 AM.
    Best regards

    Michael
    -- o --
    PC-DMIS CAD Ver. 2019 R1 SP5
    DEA Global - 09-15-08
    Renishaw PH10MQ w/ TP200 & SCR200-Rack

  • #2
    Originally posted by Mykel View Post
    Hi Guys.

    I got involved in a minor project, where I been asked 2 questions:

    1) Can the CMM check if 2 holes are connected?

    Simply drive the probe into a hole, and if it doesn't touch anything go back til the clearplane.
    If it touches anything. Take the point, and return to clearplane.

    I would like the probe to return to clearplane no matter what happens.
    Sometimes we have some smaller burrs in the hole, that makes the program come to a hold, and I'd like to prevent that.
    You can do this using the "on error" functionality providing your controller supports it. https://docs.hexagonmi.com/pcdmis/20...n_an_Error.htm

    Originally posted by Mykel View Post
    2) How do I measure the depth of a drilled hole?

    Is there a easier way, other than this one:
    Measure the diameter, make an alignment in the center of that hole, and go down into the hole until it touches the bottom of the "cone".
    Calculate the offset to where the cylinder of the hole intersects the large diameter of the "cone".

    What if the angle of the drill changes from 118° to 140°, because the CNC-guys forgot to order the "original" one in time.
    And they only have to scan their tool to find the length.
    Generally it is a bad idea to try to measure drill depths wit the CMM for precisely the reason you describe. There are too many variables involved if you just take a single point which would lead to inaccuracy and it generally requires a lot of effort for a measurement that can usually be performed much more quickly and reliably using hand tools. If it must be done on the CMM and accuracy is important then the best approach is to determine the intersection point where the drill angle meets the drill body. This is normally done by measuring a line axially along the centre line on the diameter, anther line axially along the centre line of the cone and then intersecting the two to get the shoulder point - as I said, a lot of effort and "what ifs" for what should be a very quick and basic hand tool check.


    Originally posted by Mykel View Post
    Oh, and by-the-way:
    How do I get PC-DMIS to drive the probe into a hole, and then lift it a bit up, before the diameter is measured?
    As the procedure is right now, it drives into the hole, and then go deeper for measuring the diameter.
    That's not right, I guess.

    You probably need to look at something like the "find hole" functionality within auto features. https://docs.hexagonmi.com/pcdmis/20...Properties.htm
    Neil Challinor
    PC-DMIS Product Owner

    T: +44 870 446 2667 (Hexagon UK office)
    E: [email protected]

    Comment


    • #3
      Find the bottom of a hole, then "up" to measure the hole.

      Use a NEGATIVE value for the spacer for the sample hit, and a negative value for the depth.

      To do so at the center of the hole, you would need to make a temp alignment to a CYLINDER measured in the hole.
      sigpic
      Originally posted by AndersI
      I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

      Comment


      • #4
        1) You could use the ON ERROR function to handle the behavior if the hole not found

        Also as a general rule part should be reasonably free from burrs before CMM inspection

        2) How I would proceed:
        • Measure the hole as a cylinder
        • Measure a cone at the bottom of the hole (set prehit distance according to the variability you might expect for depth and angle)
        • Create a constructed circle at the intersection of the cone and cylinder
        I'm not entirely sure about what you are asking in your last question, but I would suggest looking into starting/ending depth of the feature.

        Comment


        • #5
          The others have the ON ERROR stuff covered.

          Regarding the drill depth, its totally possible, but this is situationally dependent. Sounds like you'll need communication AND cooperation with your MFG Dept on this one.

          For example... I have one part where the customer's print has hole with a drill pnt at the bottom, drill pnt depth can vary ±0.050 and angle can be ± 10°. Before I wrote the PC DMIS program, my MFG Dept guaranteed me that the cone will always be within ±2° and the depth will be within ±0.015. This makes the part inspect-able for the CMM while supplying them with a better product. Since we have decent CNC machines, part isn't more expensive to make either. Just check the form-tool on the comparator a bit more to ensure the angle is maintained.
          Last edited by DAN_M; 11-24-2020, 07:55 AM.
          SF7107(PCD), SF454(PCD), 152614(Quindos), 9159(Quindos), 7107(Quindos), B&S Manual, M&M Gear Checker

          Comment


          • #6
            Thanks for your effort.

            I cannot measure the cone, because it's normally quite small diameters, and the effort in measuring the cone, is too much.
            I measure a ø5 hole with a ø2 probe, so I'm quite sure that the shpere on the probe touches the cone, and not the bottom og the hole, where it is flat.
            I have made a Excel-sheet that helps me calculate the offset, with a given angle.

            My CNC-guys just have to decide the angle of there drill's, or get a faulty result.


            About all your tips.
            I have something to work with now, so I'll look into it tomorrow.
            It 15:15 in Denmark, so I'm about to shut down the computer for today.

            Enogh is enogh, ey.

            Best regards

            Michael
            -- o --
            PC-DMIS CAD Ver. 2019 R1 SP5
            DEA Global - 09-15-08
            Renishaw PH10MQ w/ TP200 & SCR200-Rack

            Comment


            • #7
              There is one other possibility that I can think of to find the depth, and that is to use a pointer stylus.

              pointer stylus.JPG

              Comment


              • DAN_M
                DAN_M commented
                Editing a comment
                I have used these in the past.

                Using TP20 on a PH10M...Got STDDEV within 0.0004. Not the most accurate but it did the job

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