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Moving The Locatioin Of A Dowel Pin A Few Thou

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  • Moving The Locatioin Of A Dowel Pin A Few Thou

    In fine tuning my 24" finger brake I've notice some things that I have to correct. The biggest issue is raising the inside edge of the apron to the center of the pivot point.
    I don't want to get too far carried away here with the explanation, but here is a brief description of what I'm seeing.
    On the left side of the brake the edge of the apron is about .005 below the center of the pivot point. On the right side it's about .011 below the pivot point.
    To some that may not seem like a big deal but what happens here is when the apron is raised to make a fold the right side moves away from the edge of the fingers by the amount of error I
    mentioned. So the fold starts out being clean and sharp on the left side but gradually transitions to a smoother larger radius band going to the right. Not a big deal if 16 ga. sheet metal is being
    bent but with thinner material it's quite noticeable.

    So after filling in all the dings and imperfections along the top edge of the apron I have lowered that surface by a couple more thou. Don't care because I have to come up with a way to raise the
    apron to the center of the pivot point on both sides. The problem is the apron is located by a dowel pin on each side and to compound the issue the right side dowel pin hole is about .010 higher
    than the pin on the left side lowering the right side of the apron.

    So........... after thinking about this I think the easiest way to raise each end of the apron the needed amount would be to remove each dowel pin from the pivot arm and grind a few thou off the

    bottom side so I can raise the apron and place a sliver of the appropriate thickness shim on top of the dowel to keep the apron from dropping. then tighten the hold down bolts.


    In this pic you can see the dowel pin just below the bolt. I could also elongate the hole in the apron but would rather sacrifice the dowel pins rather than the apron.
    I hope I haven't lost anyone here !!

    Click image for larger version

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    I've indicated this thing nine ways to Sunday so I know where and where the errors lie.

    Click image for larger version

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    This is what the edge of the apron looked like. I've spent a few hours tigging all those little dings in and filing the top flat. I may set it up on the grinder and take the rest of the imperfections
    out of it. A few more thou won't matter as I can adjust for that with the dowel pin grinding and shimming.

    Click image for larger version

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    JL....................

  • #2
    Is it possible to turn a cranked dowel pin?

    Comment


    • #3
      Make an oversize dowel pin and bore for that size with both parts fixtured together.
      Davis

      "Nothing is impossible for the man who doesn't have to do it himself"

      Comment


      • #4
        Originally posted by The Artful Bodger View Post
        Is it possible to turn a cranked dowel pin?
        Not sure what you mean.

        JL.....

        Comment


        • #5
          Originally posted by interrupted_cut View Post
          Make an oversize dowel pin and bore for that size with both parts fixtured together.
          . I thought of this too. I wouldn't have to make a dowel pin just go to the next size up.
          The the ones that are in there now are 3/8". Something about .020 larger in dia. Maybe metric.
          I have to see what sizes are available.

          JL...

          Comment


          • #6
            Originally posted by JoeLee View Post
            Not sure what you mean.

            JL.....
            Take a piece long enough to make another dowel pin and somewhat bigger in diameter. Mount the piece off centre in the lathe and turn half of the length to the required diameter. Flip the piece to have the 'finished' end in in the chuck and off centre so that when you turn the remainder you have your 'cranked' dowel pin!

            Comment


            • #7
              If you know the pin offset you need
              you can make a new pin on the lathe
              and use the 4 jaw to dial in the offset amount.
              Making an offset pin,

              -Doozer
              DZER

              Comment


              • #8
                Originally posted by Doozer View Post
                If you know the pin offset you need
                you can make a new pin on the lathe
                and use the 4 jaw to dial in the offset amount.
                Making an offset pin,

                -Doozer
                Is that like what I said to do?

                Comment


                • #9
                  Offset, cranked; same idea.
                  Paul A.
                  SE Texas

                  And if you look REAL close at an analog signal,
                  You will find that it has discrete steps.

                  Comment


                  • #10
                    How about an eccentric pin

                    Comment


                    • #11
                      Am I missing something?
                      First picture you measure from top of pin - second picture you measure top of face plate.
                      Not in same plane!
                      I have tools I don't know how to use!!

                      Comment


                      • #12
                        Originally posted by Doozer View Post
                        If you know the pin offset you need
                        you can make a new pin on the lathe
                        and use the 4 jaw to dial in the offset amount.
                        Making an offset pin,

                        -Doozer
                        I had thought about grinding an off set or "crank pin" as mentioned in the previous posts.......never heard that term before.

                        But it's a lot quicker and easier to do the same 4 jaw set up on my T&C grinder and grind the needed amount off one end of the pin and position it so I can raise the apron and slip a sliver of shim on the top side of it. Same difference only a lot less work.

                        JL................

                        Comment


                        • #13
                          Originally posted by ptjw7uk View Post
                          Am I missing something?
                          First picture you measure from top of pin - second picture you measure top of face plate.
                          Not in same plane!
                          No, I don't think your missing anything........ I'm missing a lot of information on what I did and how I went about comparing the differences between the left and right side of the pivot point which I used as my datum point in relation to the top edge of the apron. Like I said I indicated this nine ways to Sunday. I just didn't get into all the details because I can't stand typing !

                          What I was doing in the two pictures was indicating the top of the pin with the dial setting on the machined surface behind the apron where the 1 1/2" x 3/4" bar is bolted down to. See third picture.

                          I was comparing the difference in pin height on each side. I zeroed my dial on the top of the left pin and compared that to the reading I took on the right pin. There was only about .004 difference between the two. That could be either the pin height or the casting surface. I don't know but It was very close.

                          I did the same thing with the left and right side of the apron and ther is a difference of about .011.

                          Either way the top of the apron needs to be exactly on the center line of the pivot point. That's where the off set dowel pin comes into play as it's the easiest way to raise each side of the apron.

                          The 1 1/2" x 3/4" bar behind the apron is just about dead on center with the pivot point on both sides. The apron sits lower, more on the right side. Hard to explain, but I know where the error lies.

                          Trust me !!

                          JL.................

                          Comment


                          • #14
                            Why not just shim the fingers when you need the crisp bends?

                            Comment


                            • #15
                              An eccentric pin would want to rotate to the lowest position under load. I'd go with correcting the location of the apron and drilling/reaming for a larger pin (10mm?).
                              Last edited by MrWhoopee; 11-13-2020, 11:10 AM.
                              It's all mind over matter.
                              If you don't mind, it don't matter.

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