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Clearances in press die

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  • Clearances in press die

    I have been asked to build a die for a friend, it is a round curved top item. He is wanting to use 11 or 12 ga steel sheet.

    I have been told by several people that clearances between male-female dies is expotential to sheet thickness. AND you have to overbend item so it will pop out of die on it's own. I know tubing sure has different elasticity in differnet pieces.

    Lost, as usual.. Looking in a Machinist refrence..


  • #2
    .009 for 12ga.
    .011 for 11ga.

    You could split the difference and make it .010.

    Here's all you ever wanted (need) to know about punch/dies.

    Click on "see chart #5" at the bottom of the page.

    [This message has been edited by CCWKen (edited 05-11-2004).]


    • #3
      Regarding punch/die clearance for making have to be careful and specify whether it's per side or on diameter. RW says overall meaning on diameter. They also say add to punch, I would think you'd add to die diameter (I guess I'm not understanding what they're saying here).

      Gypsie, are you talking about punching or forming/bending? You mention spring back which implies bending.


      • #4
        What is meant is you add the clearance to the size of the punch. Since it is the punch that determines the size of the hole, you add the clearance to the size of the hole, i.e. punch. Punch size + Clearance = Die size.

        Yea you're right; sounds like David is talking about Press clearance. My mistake, sorry.


        • #5
          I make simple bending dies all the time,my most recent was a die to bend an S shaped part out of 2x3/4" flat bar,first thing to remember is that all radiuses must be reduced on the male side to allow for the thickness of the material.The die I had built included a 3"radius out side bend on the female side of the die,that meant that my male die had to have a 2-1/4" radius on the male,hope this helps.

          Btw,making flat panel forming dies is a black art,I have done it,but I cheated and used them as hot forming dies,I heated the blanks red and pressed them allowing them to cool in the die,slow,but easier than fiddling with the die for a week.
          I just need one more tool,just one!


          • #6
            Weird: black art? Lost art I think trying to find something. They had progressive dies in the last plant I worked maintenance in. Them guys would stop work if you came around. It was all trial and error I think. They shear parts too thou, I am planning on trimming outside die after stamping.

            It is a fender male-female die for wide tire bikes. A shop up north quoted 20k.. I think.. I can do it much less.

            ROund radius nearly. both ways. different turn thou.



            • #7
              Reckon a 50 ton press will do this? next question?

              What kind of oil do they use? I have heard everything from whale tallow on. 10wt motor oil was used in the progressive dies.. it was on everything, inside electrical panels, inside rubber cord.. everywhere..



              • #8
                Some shops use whats known as "vanishing oil" on progressive setups. Looks like a very thin almost watery substance (do I hear people thinking WD-40?) which does almost totaly evaporate unless sheets are stacked up. Other times water soluable oils are used where more of a draw is required. It might make an interesting search. If I remember correctly, the "evaporating oil" was known as "Vanishing oil."
                [This message has been edited by gvasale (edited 05-12-2004).]

                [This message has been edited by gvasale (edited 05-12-2004).]

                [This message has been edited by gvasale (edited 05-12-2004).]


                • #9
                  On some dies we have at work especially the ones that produce parts that are to be welded or painted later we use Ivory dish soap 1:4 with water,the last think you want is oil residue on parts that have to be painted or welded.Punches get straight cutting oil swabbed on with a brush to stop galling.
                  I just need one more tool,just one!


                  • #10
                    Look at this:


                    It's probably a little light for your application, but might help.

                    Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                    ~Practitioner of the Electromechanical Arts~


                    • #11
                      Take a big breath, sit down, relax and ask yourself "Do I want to go down this path ?"

                      Whole new ball game, big lumps of metal, complex die shapes and programming, some of the die moulds run for days on a CNC.

                      If by fenders you mean what we know as mudguards they are usually made by rolling between a set of three shaped and geared rollers. Some have an extra set they swing into position on the last few runs to roll the bead over. Very quick and I have seen some hand operated ones many years ago.

                      John S.

                      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.


                      • #12
                        You just got the shop air conditioned, are you ready to tear out a wall to expand for a 50T punch press? Got to be a better way!
                        Guess that will give you something to do when the guvment job ends.
                        I guess a 50Ton press may sound bigger than it really is.
                        David from jax
                        A serious accident is one that money can't fix.


                        • #13
                          You guys don't know the half of it..

                          I have been asked to investigate chrome shop practises. I had money waved in front of me to use.
                          I also have been asked about a second ideal, a shop with horse stall type booths for customers to work on thier own bikes.. rent tools and sell parts.. and advice.. and mechanics for hire.. Make people tackle a larger job knowing they have a person to help with the details.. LOts of people want to build thier own bikes.. but are afraid.. Yes I got someone to hold your hand.. HA HA.. for a fee... Right now our MOtorcycle shop is just a storage barn full of corvettes and toys.. It has not been open since I went back to work.

                          Fender Die:
                          I am thinking since it is a simple form I can make the female-negative die. Now if it will work or not is another story. The person wanting it made knows I have no previous experiences.

                          I am told it taxes the cnc. Not the way I have it planned. I'll take pictures when I undertake this. You'll all laugh at my simplicity.. A roller would make more sense.. but.. I made two already that didn't work right to my happiness. One resides in front of the saw to roll materiel across.. ticks me off every time I see it.



                          • #14

                            Let me throw out a few thoughts for your consideration....

                            The dies that stamp the rear fenders for one of the current model Harleys cost $450K+/-. That's K as in thou$and. This set of dies makes one fender at a time and requires laser trimming afterwards. Probably done on a press in the 100+ ton range.

                            Detroit spends something like a billion a year on dies for new car models. Of that billion approx a third goes to reworking the dies so they produce good parts. Even with all the computer simulation and analysis of the stamping process it still remains almost as much art as science.

                            What you're up against is making a drawing die. To get a feel for the design mock up a small sample die up of wood or other easy material. Put a piece of paper in it and press. The places where the paper wrinkles or tears are areas where the metal flow has to be controlled. Flow control is handled by a blankholder which is a surrounding ring holding your blank down onto the bottom die while the upper punch draws the material to shape. Various methods are used to selectively control the blank holder pressure at the required locations.

                            IMO, one of the best introductions to this type die making is a book titled "Techniques of Pressworking Sheet Metal" by Donald Eary. It's a technical book, but an easy, understandable read. It's on ebay all the time, plus always seems to have copies. Get the second edition if possible, a little better than the first edition.

                            Actually, you might conclude that $20K is a reasonable price.

                            Do a search for the guys who make '32 coupe bodies. I think it's something like "Dearborn Deuce". They have a picture sequence showing front fender dies. Their dies are made of kirksite (a zinc alloy) and have a relatively short life span, but easier to make than tool steel version since they can be cast from a plaster mold. Their pictures don't show the blankholder which makes the process seem simpler than it really is.


                            • #15
                              Whoo hoo..

                              Even if it bends bumps, humps and wrinkles.. it is closer than stroking it in the english wheel for hours I have and pinching my stinking finger purple.. again..

                              It can be stroked in the wheel less.. if it is shaped close. is what I am getting at.
                              So? I get to sell a english wheel too.. hmm... I got about $200 in materiels, they sell for $2500.. whoo hoo.. more money..
                              Cheers lets have a beer..