Measuring Bore diameters

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  • Measuring Bore diameters

    I looking for a little help understanding what I'm doing wrong. I am trying to measure the diameter of a bore manually. Whenever I measure it, whether it be a circle with 4 hits or a cylinder with 8 hits, it measures about .001-.0015 big. This happens if the part is aligned or not. I am fairly new to this and could use some enlightenment. I have also tried different probe tips and thermal compensation. Any tips would be greatly appreciated.

    Patrick

  • #2
    What is the difference measured too? Calipers/Gage Pin? It could be your vectors, could be calibration, movement of the part when measuring, circularity. Its hard to pin point without more information.
    Are you using least square or MAX inscribed? I would check your circularity and check the bore as MAX Inscribed if you are comparing results to a pin.

    Comment


    • #3
      I am measuring a calibrated ring gauge to verify diameters as this seems to be a problem when comparing to bore gauges. CMM and ring gauge were calibrated less than a month ago and it is measuring least square. The part is being held to the table with a magnetic v-block as well.

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      • #4
        So many things here.... Are you trying to measure the ring gauge and trying to get the same size as the calibrated reported size ? Basicaly duplicating the measurement ? Manual CMM or DCC ?

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        • #5
          yes, trying to duplicate the stated size on the ring gauge, manual cmm

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          • #6
            good luck doing that with a manual machine. TOUCHSPEED is going to be the biggest issue you have. ALL hits for the probe calibration must be at the same speed and all hits for the measurement must be at the same speed as the calibration hits. Going to be pretty hard to do that to match the accuracy of a certified ring gage.

            YOU COULD try setting a slow speed with the speed control on the jogbox, then take all hits at the maximum speed you can get with the jogbox turned low, but the acceleration will also have an effect, so if you start from 2mm away for one hit and 8mm away for the next hit, the actual touch speed will be different. Different speed at contact will give different results.
            sigpic
            Originally posted by AndersI
            I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

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            • #7
              interesting. I guess i was under the impression from the company who does the calibration that the control compensates for speed. I am using a programmable CMM but trying to measure it in manual mode. Some of our parts only need a bore diameter measured and it seems writing a program for every part just to measure a bore would be time prohibitive. This is why I was trying to measure manually with the jogbox (joystick).

              Comment


              • KIRBSTER269
                KIRBSTER269 commented
                Editing a comment
                Report out your MAX and MIN. These represent your GO and NO-GO Pins. That measured result, is the average of the 2.

              • KIRBSTER269
                KIRBSTER269 commented
                Editing a comment
                depending on the age of the machine. The older ones when you did it manually, not the best of results. The newer CMMs seem to do pretty good, or from my experience.

            • #8
              Originally posted by bowhunter309 View Post
              interesting. I guess i was under the impression from the company who does the calibration that the control compensates for speed. I am using a programmable CMM but trying to measure it in manual mode. Some of our parts only need a bore diameter measured and it seems writing a program for every part just to measure a bore would be time prohibitive. This is why I was trying to measure manually with the jogbox (joystick).
              Make a single program, but use a variable for the bore size.
              A user input command for the size, then use that in the autofeature.
              (initial operator pickup/alignment left out)

              Code:
              CL2        =COMMENT/INPUT,NO,bore size
              EP1        =AUTO/CIRCLE,SHOWALLPARAMS = YES,SHOWHITS = NO
                          THEO/0,0,0,0,0,1,CL2.INPUT
                          ACTL/0,0,0,0,0,1,0
                          TARG/0,0,0,0,0,1
                          THEO_THICKNESS = 0,RECT,IN,STRAIGHT,LEAST_SQR,ONERROR = NO,$
                          AUTO MOVE = NO,DISTANCE = 7,RMEAS = None,None,None,$
                          READ POS = NO,FIND HOLE = NO,REMEASURE = NO,$
                          NUMHITS = 4,INIT = 0,PERM = 0,SPACER = 3,PITCH = 0,$
                          START ANG = 0,END ANG = 0,DEPTH = 0,$
                          ANGLE VEC = 1,0,0
              sigpic
              Originally posted by AndersI
              I've got one from September 2006 (bug ticket) which has finally been fixed in 2013.

              Comment


              • #9
                I also note that you say 8 hits for a cylinder. Taking two levels of 4 hits each is not advised with PC-Dmis. Make it two levels of five hits or three levels of three hits. Either would be preferable over two levels of 4 hits each.

                The problem is that sometimes, the system wants to interpret those eight hits as the eight corners of a cube, and before you know it, you've got different work planes, and stuff has gone kaflooey. Just one of those things you should try to avoid doing.

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                • #10
                  What sort of probe do you have?

                  Some analogue (scanning) probes don't give good results in manual mode.

                  (I'm assuming you're speaking in inches here and not mm?)

                  Even for manual hits a thou is a big difference!
                  Automettech - Automated Metrology Technology

                  Comment


                  • #11
                    Originally posted by bowhunter309 View Post
                    interesting. I guess i was under the impression from the company who does the calibration that the control compensates for speed. I am using a programmable CMM but trying to measure it in manual mode. Some of our parts only need a bore diameter measured and it seems writing a program for every part just to measure a bore would be time prohibitive. This is why I was trying to measure manually with the jogbox (joystick).
                    I may be old skool, but you and the jogbox manipulate the feature? You'll get something. Let the controller do some vector $hit (as good as jefman!) and you will get better stuff!
                    And as Matt said, your probe better be in touch speed as calibrated, or the calcs are going to get jaspered.

                    Comment


                    • #12
                      Originally posted by bowhunter309 View Post
                      interesting. I guess i was under the impression from the company who does the calibration that the control compensates for speed. I am using a programmable CMM but trying to measure it in manual mode. Some of our parts only need a bore diameter measured and it seems writing a program for every part just to measure a bore would be time prohibitive. This is why I was trying to measure manually with the jogbox (joystick).
                      In PC-DMIS you have to have a program open to measure a feature. Just add DCC before you measure the circle manually. Then with the cursor on the circle use CTL+E on the keyboard to execute that circle in DCC mode. If you want to speed it up, measure the circle with three hits. Then change the number of hits to whatever you want and let PC-DMIS equally space the hits. Then execute it in DCC mode.
                      PC-DMIS 2016.0 SP8

                      Jeff

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                      • bowhunter309
                        bowhunter309 commented
                        Editing a comment
                        Thank you for this. It seems to work great. I knew it was something I was doing wrong.

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