small arc circles

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  • small arc circles

    I'm too slow finding OLD threads about measuring radius on a small arc portions (class 10°)
    If anyone knows by heart, please point me to one

  • #2
    Well, this site WILL give you better links below your posting than you will get using the search, scroll down and see the links. Too bad you have to post first to see them, but they will then show up.
    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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    • #3
      Thanks, Matt

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      • #4
        Translate to nominal center of radius and take Radial Points along the surface. Treat basically as a profile. Report MIN MAX of radial distance. Easiest way. Or, use RAD Gage.
        Bill Jarrells
        A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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        • #5
          RAD Gage; what does it mean?

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          • #6
            radius gage
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            if you had soap on a rope it would be tied to yer ankle

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            • #7
              OK. Polar radius for 10 points.
              My RAD is 100'' ant tolerance .002
              What about probe compensation? If touching points, it should be ON - must calculate approach vector for no CAD is present.

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              • #8
                You need to set POLARVECTORCOMP=XYPL if you are taking hits with vectors in the X or Y axes, then report MAX and MIN PR
                Last edited by slesholdofthreep; 09-05-2007, 12:47 PM.
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                ASSIMILATE INTERGRATE SYNTHESIZE

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                • #9
                  Originally posted by Rob_K View Post
                  OK. Polar radius for 10 points.
                  My RAD is 100'' ant tolerance .002
                  What about probe compensation? If touching points, it should be ON - must calculate approach vector for no CAD is present.
                  Well, what I typically do is go ahead and rotate my coord system until my first hit is directly in a particular axis (usually X) and hits exactly where I want it to on the part (hope that makes sense). Then I do a pattern paste for the other points and PC DMIS will take care of all the other vector comps for me with no need for calculations. With 0.002 tolerance the fools in engineering should have put a profile on such an arc. Do you have any location tolerance for the arc? If the arc is not exactly where it is supposed to be you can get some cosine error on your comps. This is not usually a worrisome consideration but with a 100" Radius and 0.002" tolerance it sounds like the Engineering Group for the part needs some help if it isn't controlled any better than this.
                  Bill Jarrells
                  A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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                  • #10
                    Well, I guess all of this will get me where i want.
                    I did mention profile, but didn't got far.
                    Thank you all for your support

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                    • #11
                      Originally posted by Rob_K View Post
                      Well, I guess all of this will get me where i want.
                      I did mention profile, but didn't got far.
                      Thank you all for your support
                      You must be talking to people who don't understand prfile. A lot of Engineers suffer from that particular affliction

                      Good luck.
                      Bill Jarrells
                      A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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                      • #12
                        Short note about this topic: I think that in fact all described approaches are undoubtly correct... But if you are asked about the radius (single value) and there is no one that wants to hear your perfect reasons... What I miss in PC-DMIS, is calculating the circle with fixed co-ordinate position, which is a common approach for example in QUINDOS or CA. You just set the nominal position as fixed and let the software calculate the radius of a circle with that centre. A little bit like "Fixed radius", but the opposite one. Then it is up to you to set the form error to some sensate value and output the radius you are asked for...

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                        • #13
                          I have had fairly decent results from scanning the radius as an open linear and then constructing a circle from that scan.
                          Xcel & MicroVal Pfx & Global 37mr4 thru 2012mr1sp3
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                          Lord, keep Your arm around my shoulder and Your hand over my mouth. Amen.

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                          • #14
                            Originally posted by Alexander View Post
                            Short note about this topic: I think that in fact all described approaches are undoubtly correct... But if you are asked about the radius (single value) and there is no one that wants to hear your perfect reasons... What I miss in PC-DMIS, is calculating the circle with fixed co-ordinate position, which is a common approach for example in QUINDOS or CA. You just set the nominal position as fixed and let the software calculate the radius of a circle with that centre. A little bit like "Fixed radius", but the opposite one. Then it is up to you to set the form error to some sensate value and output the radius you are asked for...
                            Reporting MIN and MAX PR from fixed point is same result as you describe. Yes, it is a workaround but the result is the same as you describe.

                            Originally posted by dwade View Post
                            I have had fairly decent results from scanning the radius as an open linear and then constructing a circle from that scan.
                            Results can vary tremendously depending on material / process and get much worse the smaller section of radius you have avaliable.
                            Bill Jarrells
                            A lie can travel half way around the world while the truth is putting on its shoes. - Mark Twain

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                            • #15
                              Too bad PCDMIS doesnt have radius best fitting so that you could take the points and best fit the data to the known radius curve without the fixed axis of the radius point method.
                              Links to my utilities for PCDMIS

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