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  • sheet metal bending question

    Is it possible to bend the shape drawn in the link below on a normal box and pan brake?
    I'm no sheet metal guy and when I try to think it through my brain "brakes". :-)

    metalmagpie


  • #2
    Is it a Box and Pan Brake or just a sheet metal brake? If a B&P then I would do it as either two or three pieces. This would depend upon the size of the brake as well as the size of the part. If a plain brake the answer would be 4 pieces.

    Lay it out on some cardboard and practice your bend sequence.

    Pete

    Comment


    • #3
      Each individual bend can be made.

      They cannot ALL be made on one piece and close it, since the final piece would enclose the bender, and would not come off it, if it even fit. But you could start every bend, and then finish the last one off the bender. Order of operations would be very important!

      On a plain brake it could be ONE piece if small enough to use an offset top die.
      Last edited by J Tiers; 08-02-2016, 01:38 PM.
      CNC machines only go through the motions.

      Ideas expressed may be mine, or from anyone else in the universe.
      Not responsible for clerical errors. Or those made by lay people either.
      Number formats and units may be chosen at random depending on what day it is.
      I reserve the right to use a number system with any integer base without prior notice.
      Generalizations are understood to be "often" true, but not true in every case.

      Comment


      • #4
        Yes, no reason why you can't do that on a box and pan brake.

        Sorry, just looked at it again and maybe not Stu
        Last edited by Stu; 08-02-2016, 01:43 PM.

        Comment


        • #5
          Not with the usual generic brakes. Your fold lines are crossing the other flanges and faces. And that is the thing that makes it a deal killer for any typical bending brake. Because of the fold lines extending across the faces of the other surfaces any brake with even one long fixed or folding jaw is going to try to bend parts that you don't want to bend.

          I'm not sure what they call the other sort of brake but to do this part you need a brake which uses interchangeable upper and lower fingers. The lower fingers having a notch and the upper fingers being the rib that forces the metal down into the notch to bend it. With selectable fingers for both upper and lower pieces you can fit the bending fingers to the lengths of the flange bend lines and fit between the parts to either side that you don't want to bend.

          On top of that you can't close the box on ANY brake. It would need to be done in two parts unless you're willing to fabricate a "fit through" bending arm that uses a beam or ram that is open on one end so it can fit into the box section you want to make.

          So it CAN be done. But it can NOT be done on the usual long fold up sort of finger brake. Or on the regular 3 in 1 style sheet metal tool.
          Last edited by BCRider; 08-02-2016, 02:29 PM.
          Chilliwack BC, Canada

          Comment


          • #6
            Clarification:

            1. I have a box and pan brake aka finger brake, NOT a regular sheet metal brake, NOT a 3-in-1.
            2. The sheet metal is thin and the sections are long enough so that even after I made the last
            bend to close the box, I believe it would spring open far enough to remove it, without exceeding
            the elastic limit of the sheet metal.

            Thanks,

            metalmagpie

            Comment


            • #7
              You've not shown the bend angles but assuming they're all 90 degrees you'd have to break that down into two sections--with the joint in the middle--add a flange to join the two and use a press brake with a sectional die and punch. Can't be done on a box and pan brake because the short inner flanges overlap the folding frame...
              Keith
              __________________________
              Just one project too many--that's what finally got him...

              Comment


              • #8
                Being that thin and springy you could close the bends by some amount then finish them in mid air by hand. But the flanges need to be bent first and that is going to restrict a lot of the ability to flex.

                In any event the flange bends still cannot be done on a regular finger brake. And the flange bends need to be done first or it won't fit into any brake of any sort after the box bends are done.
                Chilliwack BC, Canada

                Comment


                • #9
                  Originally posted by BCRider View Post
                  Not with the usual generic brakes. Your fold lines are crossing the other flanges and faces. And that is the thing that makes it a deal killer for any typical bending brake. Because of the fold lines extending across the faces of the other surfaces any brake with even one long fixed or folding jaw is going to try to bend parts that you don't want to bend...
                  That's the key. It's the inner (short) flanges that are the problem. Won't work on any folder style brake...

                  ...I'm not sure what they call the other sort of brake but to do this part you need a brake which uses interchangeable upper and lower fingers.
                  You're thinking of a press brake. The bottom die is a Vee shape and the punches move vertically. If you have a die and punch of the right length you can bend that piece in two sections. Technically the bottom die doesn't have to be the exact length as long as it's short enough that you can work off one end of it...
                  Keith
                  __________________________
                  Just one project too many--that's what finally got him...

                  Comment


                  • #10
                    I would do the flanges first.

                    Then do the main bends as far as possible with equal angles but not to closing. The two end bends could then probably be brought all the way on the brake or at least close to it. That just leaves one in the middle.

                    Then finish closing it by hand. The flanges will add stiffness to keep the individual sides flat for this.
                    Last edited by Paul Alciatore; 08-02-2016, 03:01 PM.
                    Paul A.
                    SE Texas

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

                    Comment


                    • #11
                      OK, seems like there's general consensus it won't work. I'll make the part in two pieces and add a joining tab.

                      Thanks!

                      metalmagpie

                      Comment


                      • #12
                        Even if done in two parts you've still got the issue that the fold lines for the flanges are crossing the other flanges. That won't work either.

                        With a regular finger brake the only way to do this is with four pieces. Two would be flanges on all four sides and the other two would have flanges on just the two sides with plain edges that fit to the flanges on the other two full pan pieces to form your truncated pyramid shape.
                        Chilliwack BC, Canada

                        Comment


                        • #13
                          Originally posted by metalmagpie View Post
                          OK, seems like there's general consensus it won't work. I'll make the part in two pieces and add a joining tab.

                          Thanks!

                          metalmagpie
                          I say it CAN be made. Been designing sheet metal off and on for 30 years, and have used B&P brakes. The key is the fact that you can use thinner (narrower than bend) fingers, to avoid the flanges. I would bend up all the flanges, and then form up as many of the sides as will fit, possibly hand bending the last to finish after starting them.

                          I totally do NOT understand the comment about crossing bends, All the bends seem to me to end with clearance.

                          With a regular bending brake, a side offset (we called it a hatchet) tool would allow the box to close over it and be removed to the open side.
                          Last edited by J Tiers; 08-02-2016, 03:47 PM.
                          CNC machines only go through the motions.

                          Ideas expressed may be mine, or from anyone else in the universe.
                          Not responsible for clerical errors. Or those made by lay people either.
                          Number formats and units may be chosen at random depending on what day it is.
                          I reserve the right to use a number system with any integer base without prior notice.
                          Generalizations are understood to be "often" true, but not true in every case.

                          Comment


                          • #14
                            Originally posted by J Tiers View Post
                            ....I totally do NOT understand the comment about crossing bends, All the bends seem to me to end with clearance......
                            It's not an end clearance issue where the flanges meet. It's that when one flange is clamped down for bending that portions of the adjacent flanges or faces are crossing over the bend axis and will be bent up when the bending leaf is raised. The fingers might only be as wide as required for that one flange but the design of this part has the bend lines for the flanges crossing the other parts. So when you clamp down to do one flange the bending leaf will bend the other parts that are sticking out when you raise it for the bend.

                            If the goal is to bend the flanges inwards then perhaps the pyramid bends can be done first and the bends flexed in to form the pyramid. The resulting shape can then use the fingers to bend the flanges inward. But the box will prevent the flanges being more than half bent. So the flange bends would need to be finished up by hand. On the other hand if any the flanges are to be bent outward then this won't work either because of the lip of the bending leaf getting into the way.

                            I worked for a couple of years in a sheet metal shop doing radio equipment parts in my late teens as well as occasional parts on brakes belonging to generous buddies. This part to my eyes is a classic case of "you can't get there from here" for the most part. Done in thin flexible tin plate it can be started on the brake and finished with hand work. But if is a thicker material then it can't be done on a finger style brake at all.
                            Chilliwack BC, Canada

                            Comment


                            • #15
                              As I understand you, you are really saying is that there need to be "eyes" put in at the corners. Yes, that will prevent bumps. It's a design detail that is a level down from the question as I understand it.

                              That does not jive with your statement, quite.

                              Maybe you are saying that the tabs will collide with the edge of the finger. That is something that can be dealt with also, either a trapezoidal finger that tapers in from the length of the edge to something narrower (amazing how handy THOSE are), or just not bending the last bit against a finger. You can sometimes get away with that when there is a strengthening tab.

                              If that is what you mean, then you are saying that a rectangular box could be bent, but that the angled box will have issues.


                              I think the question REALLY is "can a form like this be bent up with the B&P bender. And that answer is yes, with provisions taken, so long as the box is not too angular..

                              Presumably, the OP has a shop, and could turn out a suitable trapezoidal finger to take care of the issue.
                              Last edited by J Tiers; 08-02-2016, 06:38 PM.
                              CNC machines only go through the motions.

                              Ideas expressed may be mine, or from anyone else in the universe.
                              Not responsible for clerical errors. Or those made by lay people either.
                              Number formats and units may be chosen at random depending on what day it is.
                              I reserve the right to use a number system with any integer base without prior notice.
                              Generalizations are understood to be "often" true, but not true in every case.

                              Comment

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