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  • Two questions : Warning machining content.

    1. I need to press in a small piece of brass into a hole .190" diam. and .188" thick and it needs to hold. How much should the plug be over sized??

    2. I need to bend a 3/16" deep flange of .040" thick steel around a former. Can it be annealed and then bent/hammered around the former or does it need to be worked hot??
    The shortest distance between two points is a circle of infinite diameter.

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

  • #2
    Loose Nut---This may be a case of the blind leading the blind, but on something that small, I would suggest .0005 oversize and use Loctite. As far as bending the steel is concerned, it's a "try it and see" situation. If it is a straight, non complex flange, it might bend cold. If it has any curves or complexity, then heat will certainly help.---Brian
    Brian Rupnow

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    • #3
      Normally the press fit rule of thumb is .001 per inch of diameter.
      Your size is 20 % of one inch, so .0002" will work. You didn't say if there is a hole/bore in the brass piece ?
      If so, then the press size must be larger and .0005 is a good suggestion from Brian.
      Shrink fits are twice as strong as press fits, but to get a .0002" steel hole to open to the over-sized brass, takes 300 (F) degrees in temperature differential. So if you can heat the steel to 500 and cool the brass in the freezer . it will be a push fit and really lock up when they reach equilibrium.

      The steel sheet could be formed into a flange with a sharp steel form and a leather mallet
      Thats what I would do --no sweat.
      Second choice is a dead blow or lead hammer
      Last is a ball peen hammer with a 3 inch wide piece of maple wood between the steel and hammer.
      You want to make the bend gradually (slowly) moving up and down the bend to prevent the flange
      from being stretched and bowing the main sheet . Hard hammers tend to do that !

      Rich

      No annealing required..BUT you must clamp the steel sheet on the top so only the flange material is exposed
      ( delete my "sharp steel " comment as you already have a form. )
      Last edited by Rich Carlstedt; 02-03-2015, 09:08 PM.

      Comment


      • #4
        Rich---Press fits make me shiver all over!!! I find that trying to hold a .0005 tolerance is almost more than my machines (or I) are capable of. So much is dependent on the surface finish of the parts that are being mated. The only way I have had more or less repeatable results is to finish the hole first, then turn the part being pressed into it to about .002" to .003" oversize, then sneak up on the actual .0005" oversize by using 220 grit emery cloth. This not only helps to prevent a "fall through" fit, but also knocks down the microscopic ridges left by my cutting tool that give false readings with a micrometer.---Brian
        Brian Rupnow

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        • #5
          Originally posted by loose nut View Post
          1. I need to press in a small piece of brass into a hole .190" diam. and .188" thick and it needs to hold. How much should the plug be over sized?? ...
          Pretty small... can you make it slip-fit but longer and then just peen it into the hole, cleaning up the surface later? If you have access to both sides, maybe add a little bit of chamfer on the hole that the brass can mush into? In other words, rather than cutting the brass down to the best-you-can-do exact press-fit size, mash it bigger to the EXACT size. That much brass should move fairly easy. It sounds like what you want is a rivet. Place, set, draw file to finish flush? Just thinking outside the box... but I don't know all the requirements.

          David...
          http://fixerdave.blogspot.com/

          Comment


          • #6
            Mr. Rupnow,
            Lots of people manning the oars in that boat.

            Comment


            • #7
              The piece in question is a part with a hole I drilled out oversize because I drilled the first hole in the wrong place. I want to press in a plug and re-drill the hole in the right place. I can't solder it in place or heat it up for a shrink fit because the part has several bits solder on to it already. I did try using epoxy but it broke free while re-drilling the new hole. I don't know if Loctite will work any better???

              Thanks
              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
                Consider tapping the plate, fine thread, use matching brass screw, cut off, peen.
                Or drop in a dutch pin.
                Loctite will work better.

                Comment


                • #9
                  Loctite will hold much, much better than epoxy. You have to have both pieces really clean though, and give it at least 24 hours of drying time.--And press fit is good if you can get the tolerances tight enough. How do I know---Because I have screwed up enough times exactly the same way, and fixed the screw up using the method I recommend, and the fixes worked.
                  Brian Rupnow

                  Comment


                  • #10
                    How about this, stick a taper reamer in, ream and turn a taper plug, don't worry about diameter, stick it in the hole, if the taper fits the plug does
                    Trim
                    Mark

                    Comment


                    • #11
                      How about putting a light, straight knurl on the brass and press it in? Or lightly countersink the hole on both sides, insert brass, peen both sides, i.e., make a solid rivet & file/grind flat.

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                      • #12
                        Originally posted by boslab View Post
                        How about this, stick a taper reamer in, ream and turn a taper plug, don't worry about diameter, stick it in the hole, if the taper fits the plug does
                        Trim
                        Mark
                        +1
                        on a thru hole, if you have access to both sides, put a slight back-ream on the under-side.
                        the pressed in pin, cut off a tad long, can be back-peened, like a rivet.

                        Comment


                        • #13
                          Originally posted by Old Hat View Post
                          +1
                          on a thru hole, if you have access to both sides, put a slight back-ream on the under-side.
                          the pressed in pin, cut off a tad long, can be back-peened, like a rivet.
                          I like that, didn't occur to me, thanks
                          Mark

                          Comment


                          • #14
                            Originally posted by loose nut View Post
                            1. I need to press in a small piece of brass into a hole .190" diam. and .188" thick and it needs to hold. How much should the plug be over sized??

                            2. I need to bend a 3/16" deep flange of .040" thick steel around a former. Can it be annealed and then bent/hammered around the former or does it need to be worked hot??
                            I like how you have to warn this forum of machining content. In other forums they might warn of off-topic content.

                            0.005" interference. Might need to warm or cool one part to fit.

                            Yes.

                            Comment


                            • #15
                              Take a look at tolerance rings if press fits make you sweat. They are designed to reduce tolerances to levels mere mortals can achieve every day.

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