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  • wiggler accuacy problem

    When trying to test the accuracy of my mill DRO's I placed a 4" gauge block in the machine vise so that the "good" surfaces where facing the sides of the vise, picked up one end of the gauge with the wiggler zeroed the X scale and repeated several times to check the reading, always getting 0.000" (DRO readout set to 3 decimal places for this test). Next I moved to the other end and picked it up, should read 4.100" (gauge block plus diam. of wiggler end) but consistently got a 0.004" to 0.006" (usually 0.004") undersized reading while repeating this several times.

    I checked the size of the block, a cheap set admittedly but still on size, as accurate as my mic could tell and the end of the wiggler (Starret) which was within .0002" of the 0.100 diam it is suppose to be. Size errors here would not account for the degree of error showing up.

    Thinking that there would be something wrong with the DRO I repeated the experiment with the .5, 1 and 2" blocks and every time I got the error same, .004 to .006" undersize. If the scales where off the error should be linear, say .001" /inch of travel not always the same.

    I thought that there might be some flex in the mounting of the read head but every time I moved to the other end and picked up the original starting point it is always 0.000", if there was any flex in the mounting it should show up there.

    If it is my ability to use the wiggler that is at fault why am I able to get consistent readings in any one place.

    Any thoughts, I'm stumped. Thanks in advance.
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

  • #2
    Years ago I had a big ol fight with my brother. he said I bored some holes 12.002" apart when they wanted 12.000"

    I told him to stick them 16" x 2" x 4" blocks of steel up his butt.

    Once again it went on a farm machine and with the old beater mill it was fine.

    dont ask too much from an old machine or a small china machine. +.002 is damn good for a old beater. so I told him to kiss my ass. he later admited he was being an ass and let it go.

    Comment


    • #3
      Are you using a wiggler?
      Or an edge finder like this one:
      http://www.starrett.com/pages/1512_t...dge_finder.cfm

      There are various techniques for each, of course.

      I generally get better accuracy and repeatability with an edge finder. I happened to check repeatability of an edge finder vs my DRO a couple weeks ago and it was mostly 4 tenths but occasionally 7 tenths. Surface roughness, oil on the surface and eyesight plus judgment affect the result. My repeatability with a wiggler was 1.5 thou (and it takes more concentration).

      One thing that might help determine where the discrepancy originates would be to set up a long travel indicator on table position. This should prove the DRO is accurate over modest distances and allow you to then check your technique on using your finder.

      If you get really into this you might want a Moore edge finder:
      http://mooretool.thomasnet.com/item/...=prod&filter=0

      But check the price, it might be a consideration...

      John

      Comment


      • #4
        Are you using a wiggler or an edge finder? I would not trust a wiggler to find an edge with much precision. An edge finder would be best.

        If the end of the "wiggler you used was .100" and you "0" the starting end and go to the other end it should show .050" longer than the 4,000" block not .100". That is because your measurement is taken from the center of the spindle to the edge of the "wiggler". If you did not "0" the DRO at the start end and went to the other end then you would have 4.100".

        When you "0" an edge finder or what ever your using to find the edge you use half the diameter of the edge finder, wiggler or dowel pin to move the table and "0" the DRO.

        As to why your getting a .004"-.006" error the only thing I can guess is it's the "wiggler" and you should try using an edge finder.
        It's only ink and paper

        Comment


        • #5
          It is a "old fashion" wiggler not an edge finder as in your link and I can usually get a repeatability of less then a thou. with it. As for the equipment it is a fairly new mill and brand new Fagor DRO's.

          I know for most things I don't need super accuracy but having an error like this is a bit unnerving, it shouldn't be there and I can't find the source.
          The shortest distance between two points is a circle of infinite diameter.

          Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

          Comment


          • #6
            Originally posted by Carld
            If the end of the "wiggler you used was .100" and you "0" the starting end and go to the other end it should show .050" longer than the 4,000" block not .100". That is because your measurement is taken from the center of the spindle to the edge of the "wiggler". If you did not "0" the DRO at the start end and went to the other end then you would have 4.100".
            .
            I zeroed the X scale but did not move it over half the diam. (0.050") on either end hence the 4.100" readings.
            The shortest distance between two points is a circle of infinite diameter.

            Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

            Comment


            • #7
              Originally posted by GadgetBuilder
              One thing that might help determine where the discrepancy originates would be to set up a long travel indicator on table position. This should prove the DRO is accurate over modest distances and allow you to then check your technique on using your finder.
              John
              I have an edge finder, that works with an offset indicator, similar to the Mooretool one in your link, I'll try it next. As for using an indicator as a check, if you get an error which one is wrong.
              The shortest distance between two points is a circle of infinite diameter.

              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

              Comment


              • #8
                Ok, but it is strange that your getting an error when you say you can get within .001" with the wiggler. I just don't trust a wiggler except for locating crosshairs to drill a hole.

                Call Fagor or the people you bought it from and ask them about what you are getting.
                It's only ink and paper

                Comment


                • #9
                  Make sure the JO block is dead parallel . Pick up the end 0 move to other end in one direction DO not back up . Hold another JO block tight to the face on the 4 inch block and continuer move until edge finder clicks off. That is your reading Should read 4.100.
                  The way I do it is with a set of micrometer standers and 2 v blocks clamped to the Table . And you stop one end of the slandered against a 123 block and you can keep changing out to longer standers and check the whole table travel for error.
                  Every Mans Work Is A Portrait of Him Self
                  http://sites.google.com/site/machinistsite/TWO-BUDDIES
                  http://s178.photobucket.com/user/lan...?sort=3&page=1

                  Comment


                  • #10
                    Carl,

                    I believe he states he gets repeatability within .001". Not accuracy.

                    It could be 1/4" from the true edge and still repeat within .001" every time.

                    Comment


                    • #11
                      Carld, I agree with you on the error, it doesn't make any sense. If the Dro was a fault then after moving the table back and forth several times, as many as 20 times, if it was at fault, bad scale or loose mountings, when I go back to the original starting point it should show a discrepancy but it is always 0.000, never varies and as I stated earlier the error is always the same regardless of the distance travelled, that doesn't sound like a scale error.

                      I would expect some small error but not 5 or 6 thou. Must be me or the wiggler, I'll try the edge finder next.
                      The shortest distance between two points is a circle of infinite diameter.

                      Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                      Comment


                      • #12
                        Originally posted by lane
                        Make sure the JO block is dead parallel . Pick up the end 0 move to other end in one direction DO not back up . Hold another JO block tight to the face on the 4 inch block and continuer move until edge finder clicks off. That is your reading Should read 4.100.
                        The way I do it is with a set of micrometer standers and 2 v blocks clamped to the Table . And you stop one end of the slandered against a 123 block and you can keep changing out to longer standers and check the whole table travel for error.
                        The vise was indicated parallel to the ways. I'll give it a try but I thought the whole point of using DRO's was so that you didn't have to worry about backlash and such things, the scales are independent of the leadscrew, why would moving it backwards be a problem.
                        The shortest distance between two points is a circle of infinite diameter.

                        Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                        Comment


                        • #13
                          Originally posted by loose nut
                          I have an edge finder, that works with an offset indicator, similar to the Mooretool one in your link, I'll try it next. As for using an indicator as a check, if you get an error which one is wrong.
                          You seem to have gauge blocks so proving the long travel indicator correct should be possible for, say, the 0.5" range without too much effort.

                          If you have something similar to the Moore edge finder try reading both sides of the finder, then use the mid point. This should cancel finder or technique error.

                          John

                          Comment


                          • #14
                            Just use a DTI and Lane's method without the math.

                            Lay the long gage block on the table with another gage block against one end that sticks up just enough to create about a .100" step and indicate it parallel with the X travel. Touch one end with the DTI and note the reading. Zero the DRO. Move to the step and touch it until the same reading is obtained and the reading on the DRO will be the distance traveled.

                            I don't understand the reluctance on this site to using simple tools like DTI's

                            Tasks such as indicating vises, centering over bores, checking squareness, finding edges, etc. really should not be such daunting tasks as all can be accomplished easily with a simple DTI!
                            Last edited by Glenn Wegman; 10-25-2009, 08:24 PM.

                            Comment


                            • #15
                              Originally posted by GadgetBuilder
                              You seem to have gauge blocks so proving the long travel indicator correct should be possible for, say, the 0.5" range without too much effort.
                              John
                              That sound is me hitting my head against the table, I should have picked up on that before. So the whole day wasn't wasted I did learn something new.
                              The shortest distance between two points is a circle of infinite diameter.

                              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

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