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Making / Grinding An Offset Dowel Pin

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  • Making / Grinding An Offset Dowel Pin

    I'm at the point in this restoration project where it's time make the off set dowel pins for my finger brake apron.

    Some of this was discussed here a couple weeks ago. https://bbs.homeshopmachinist.net/fo...pin-a-few-thou


    I need to make two offset dowel pins, both are .375 in dia. The left has to be offset by .014 and the right has to be offset by .022. Both ends of the pins will be .375 in dia. when finished.
    The end of the pins that goes into the apron will be -.0002 for ease of fitting the apron onto the pivot arms. The length of both pins is 1.5". 3/4" taps into the pivot arm and 3/4" slips into the apron.

    Here is my diagram. Left pin needs to be offset by .014 and the right side pin needs to be offset by .022. This will bring each end of the apron dead center on the pivot point.

    Click image for larger version  Name:	IMG-20201222-105117.jpg Views:	0 Size:	109.0 KB ID:	1917205

    Apron and pin location.

    Click image for larger version  Name:	IMG-20201222-105258.jpg Views:	0 Size:	269.6 KB ID:	1917206

    The pin is tap fitted into the pivot arm and will be replaced with the pin with the appropriate offset.

    Click image for larger version  Name:	IMG-20201222-110014.jpg Views:	0 Size:	212.6 KB ID:	1917207

    So my questions are as follows...........

    I have some 7/16" dia. .437 pins and also some 10MM .394 ones. Which ones would be best to use?? I don't mind grinding a little extra off to get to my finish dimensions.

    The process.......... This is how I'm thinking of going about it.

    Using my T&C grinder, grind half of the pin down to .375. Then put the .375 end in the 4 jaw chuck, offset it by the .022 which is the amount needed for the right side pin, then grind that end down to .375 -.0002. Repeat the process for the left side pin. Of course I'll grind both pins down to the .375 before putting the 4 jaw in the work head, no need to R&R tooling twice.

    Does this sound like the right approach for the job or can someone suggest something better / easier.
    I don't want to turn a 1 1/2 hour grinding project into a 4 day experiment.

    Not sure if the 10MM pin is going to be big enough in dia to cover the amount of off set for the pin requiring .022 off set.

    JL....................
    Last edited by JoeLee; 12-22-2020, 12:44 PM.

  • #2
    Use the 7/16".

    Comment


    • #3
      JoeLee. For your offsets, rather than faffing about with a 4 jaw what I often do is make an aluminium sub-collet in which I can bore the offset hole on the milling machine. This is obviously of real value in making multiple items but I have found that it is much easier than dialling in a four jaw, particularly with smaller diameter items.
      West Sussex UK

      Comment


      • #4
        Perfect job for a Harig grind-all and surface grinder. Lacking that, your 4 jaw approach seems reasonable for the job at hand.

        Comment


        • #5
          It does not seem as if you have the material in the 0.394 pins.... That is only 0.019 larger, and one of the pins will be 0.022 offset.. The offset plus the diameter needs to fit inside the material.

          And even then, you will need to grind the initial 0.375 offset to one side of the stock to have enough left.

          If you just grind the first one to 0.375 concentrically, you need stock 0.044 larger in diameter (minimum) for the other portion to stay all in the metal.

          Are the pins case hardened or through hardened? You might run into soft material if you grind off a lot from the 0.437 parts.
          2801 3147 6749 8779 4900 4900 4900

          Keep eye on ball.
          Hashim Khan


          It's just a box of rain, I don't know who put it there.

          Comment


          • #6
            I would favour Alan Smiths eccentric sub collet method if you have the means to make one. Perhaps turning just oversize. drilling and reaming, then offsetting in the four jaw and finishing the od. You would have to make several.

            Comment


            • #7
              I think its a good question. Are they case hardened.?

              Comment


              • #8
                Originally posted by Alan Smith View Post
                JoeLee. For your offsets, rather than faffing about with a 4 jaw what I often do is make an aluminium sub-collet in which I can bore the offset hole on the milling machine. This is obviously of real value in making multiple items but I have found that it is much easier than dialling in a four jaw, particularly with smaller diameter items.
                That is a good idea!!! I make them all the time for turning small dia. things that are too small for my chuck, easy drill and slit so it tightens up on the part when the chuck is closed.

                But I never made an off set one ! I may run into some error swapping collets in the grinders work head. I would like to do this all in one collet if I could.


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

                Comment


                • #9
                  Originally posted by J Tiers View Post
                  It does not seem as if you have the material in the 0.394 pins.... That is only 0.019 larger, and one of the pins will be 0.022 offset.. The offset plus the diameter needs to fit inside the material.

                  And even then, you will need to grind the initial 0.375 offset to one side of the stock to have enough left.

                  If you just grind the first one to 0.375 concentrically, you need stock 0.044 larger in diameter (minimum) for the other portion to stay all in the metal.

                  Are the pins case hardened or through hardened? You might run into soft material if you grind off a lot from the 0.437 parts.
                  Yes, this is what I've figured, had to think about it for a second.

                  I need the dia. plus double the offset.

                  Not sure if the pins are hardened throughout, I'm assuming they are. I always thought all hardened dowel pins were, at least standard ones. All the ones I've ever had to cut or trim were hard all the way through.

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


                  Comment


                  • #10
                    Originally posted by plunger View Post
                    I think its a good question. Are they case hardened.?
                    I'm assuming since they are standard pins they are hardened throughout. Any other type would be a special not easily found.

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

                    Comment


                    • #11
                      Originally posted by old mart View Post
                      I would favour Alan Smiths eccentric sub collet method if you have the means to make one. Perhaps turning just oversize. drilling and reaming, then offsetting in the four jaw and finishing the od. You would have to make several.
                      I do have the means to make the offset collets. I would have to make two of them anyway, one for the pin that needs to be off set at .022 and one for the pin requiring .014 offset. Just not sure how close I can hold that off set tolerance by drilling it out on the mill. Easy enough to try.

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

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                      • #12
                        AND just how will you be able to orient them to the required angular requirement to take advantage of all those "tenths" ???
                        ...lew...

                        Comment


                        • #13
                          If you have a lathe, it would be better for the hole drilling and a solid carbide drill, even better.

                          Comment


                          • #14
                            Originally posted by Lew Hartswick View Post
                            AND just how will you be able to orient them to the required angular requirement to take advantage of all those "tenths" ???
                            ...lew...
                            Probably pretty much just by looking at them. I could indicate the high spot and Mark it,
                            5 or 10 degrees either way off the centerline of the high spot isn't going to amount to much.
                            Not going to try and hold tenths here, just not critical.
                            if I can get that apron within a couple thou of the pivot centerline it'll be good.

                            JL.....

                            Comment


                            • #15
                              Originally posted by Dan Dubeau View Post
                              Perfect job for a Harig grind-all and surface grinder. Lacking that, your 4 jaw approach seems reasonable for the job at hand.
                              That is what I was thinking.
                              Set the offset for the vee block on the surface plate
                              and spin the pin on the grinder.
                              Then Bob's your daddy.

                              -Doozer
                              DZER

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