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sheet metal bending question

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  • #16
    One of these would probably work:
    Magnetic Sheet Metal BrakeThe BB-4816M is a unique magnetic box and pan brake that has endless bending possibilities when compared to conventional sheet meta...

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    • #17
      JTiers, you've missed the forest by focusing on the tree. Or the fingers in this case. It's not corner clearance to avoid bumps or grouping the fingers to fit the length of the side with clearance outside of the fingers.

      Picture the brake and how the piece needs to be held in place to catch only one of the flanges. When the bend line of the desired flange is set at the right point triangular portions of the other flanges to each side are laying over the bending line and will be bent as well when you raise the front bending leaf. And it makes no difference if we clamp with the main part under the fingers or with only a flange under the fingers.

      I wish it were easier to post pictures to this site. I'd rattle off a quick sketch that would make it clear in a blink. But having to post it to Photobucket then to leave it there so it remains visible in this thread is more trouble than it's worth.

      Metalfixer, that won't work either. It's still has a full length bending leaf. And that's the issue. And that one, cool though it is with the magnetic clamping, doesn't even have selectable fingers to clear flanges that are already bent. It's for simple bends only.
      Chilliwack BC, Canada

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      • #18
        Originally posted by BCRider View Post
        Metalfixer, that won't work either. It's still has a full length bending leaf. And that's the issue. And that one, cool though it is with the magnetic clamping, doesn't even have selectable fingers to clear flanges that are already bent. It's for simple bends only.
        It works with less-than-full-width finger plates as well. Would likely still run into problems fouling the other flanges due to the full width bending leaf, but a flange-width finger is no problem.

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        • #19
          It's really two flanges that are the problem you refer to, where the curve hangs over the bend.

          All the outside of the "circle" seems to be fine.

          The end ones can be bent by hanging them over the end of the machine to clear the unbent parts. But you are probably right since not all benders allow that and his may not. Whatever we had at a prior employer could, and I have done that.

          The two middle flanges on the "inside" I think would have to be bent after bending some of the "box side" bends so they clear the angle. THOSE are the ones that overlap in a way that can be a problem. If the box sides can be bent up they may clear, that is what I am suggesting. It will depend, as I mentioned, on how angular, and large the box is. Past a certain point it's probably not going to work, and that will depend on the bender. If it's a few inches, as I assumed just from considering a B&P, it should.

          The box sides have to clear the finger and the support, but be bent enough to not hit the table. So after bending the first of the two, it may need to be unbent a little to clear the finger for the second. At a matter of 4" or so it would work on the one I have used, especially with a narrowed finger so it's easy to get the part over it.

          Not so much of an issue with a regular brake, but to close the box you need a hatchet top die.

          If he needs just one, I bet he can bend it as far as he can in the bender, and finish outside, almost no matter what he has for a B&P.
          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.

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          • #20
            No, the outer ones as shown have the same issue. On the inner arc the bend line for each flange extends into the side panels. On the outer flanges the bend lines cross over the adjacent flanges at an angle from the inside corner to somewhere near the middle of the flange on the outer edge. So it's still a non starter if we're trying to bend the flanges in the middle of the brake.

            Looking a bit closer at pictures of some brakes I think you're right about some being able to overhang the panel to the side and bend the outside flanges. A few seem have the pivot hinges set slightly below the line of the bend and the bend line is more of a virtual bend axis as there's a gap to deal with. On that style we can overhang the panel to the outside and bend that first flange. The pictures of those I'm seeing are smaller more home and light duty style brakes. On the bigger and more heavy duty style brakes the housings for the bending leaf pivot are solidly in the way. All the brakes I've used are this last style.

            I'm trying to see how the rest of the flanges can be bent provided it's a brake that allows overhanging the panels for the first flange. The outer curve flanges are fine if we can start with the overhanging bends for the outer two. but the inside flanges are a bugger because the adjacent sides are still in the way unless it's bend to the final pyramidal shape to start out. But then we can't bend the flanges down into place more than by a little. I think it would be well worth working with a cardboard model to work out the bending order. It ain't going to be simple by any means if it's possible at all.

            Really it's not the pyramidal bends. It's just the flanges. I'm thinking that they way to do this is use small pieces of bar stock cut to the length of the flanges. Clamp them to the flange along the bend line and bend away. Do the outer flanges first so you can cut down the pieces and then do the smaller "inner curve" flanges. Finally finish the seam flange and pyramidal bends in the regular brake.

            It occurs to me that a neat trick would be a bending leaf that uses a "virtual pivot" made up of multiple arms or two or three bearings running in an arc shaped track under the table so that there doesn't need to be any pivot housings at the ends of the bending leaf and clamp down table.
            Chilliwack BC, Canada

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            • #21
              Moot now, decided to brute-force it and make 4 separate parts. The good part is that I can rough cut them with power shears and then do most of the rest of the cutting on my buddy's 24" shear. The layout lines are pretty faint in the picture, but I think they're visible if you look closely.

              metalmagpie

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              • #22
                It's moot in more ways than that. I thought it was much smaller,and at the size you show, most brakes have no chance of any "finessing" to do the job. The pieces are a lot bigger than the finger length

                BCR:

                The way I have gotten away with stuff like that is to bend what you are calling the "pyramidal" bends (I called them "box bends"), and then "finesse" the box around the finger. With the box at least partly formed, the overlap bend can be out of the way.

                With that one, it may not be possible to fully form the last flange, or it might be possible if one of the others is "unbent" somewhat so it hangs off the side.

                I'll concede it's not a production process. But the B&P isn't really a production machine. It's more of a prototype shop tool, and you end up doing whatever to get the job done for 1 to maybe 5 of them.

                The bends can be done with a regular bending brake, since you have your choice of lengths of bottom and top die. Some homeshop type brakes, like the common 3 in one (shear, bender and roller), have a single full width bottom doe, and they don't allow that option, even though you can replace the top dies.
                Last edited by J Tiers; 08-02-2016, 11:12 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


                • #23
                  Some box and pan brakes allow you to drop the lower jaw and you can then insert a short block to clamp the metal and then there would be room for the flange to clear.

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                  • #24
                    It's not just the flange, it's the whole "half circle".

                    It curves around and the extended bend line goes across metal for the 4 flanges on the "inner circle" of 4 flanges. The metal either needs to be elsewhere, i.e. already bent and out of the way, OR someplace has to be made for it to move without hitting part of the machine.

                    A machine that allows a bend on the end, with material hanging off the table, is capable of making at least the outside two.

                    In some cases, bending up the outside two panels will allow repeating the "outside the end" bend on the next two, which is what I would try to do. The actual piece is so big that may not work too well
                    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


                    • #25
                      The bends can be done with a regular bending brake, since you have your choice of lengths of bottom and top die. Some home shop type brakes, like the common 3 in one (shear, bender and roller), have a single full width bottom die, and they don't allow that option, even though you can replace the top dies.
                      Yep, that's what I figured too earlier. Such a brake would solve the issues to a "T".

                      The way I have gotten away with stuff like that is to bend what you are calling the "pyramidal" bends (I called them "box bends"), and then "finesse" the box around the finger. With the box at least partly formed, the overlap bend can be out of the way.
                      I've done my share of that too. And in this case it would likely work fine since Paul confirmed that it was being done in thin metal which could be creased at least on the brake then finished up with hand forming. If the flanges themselves had a nice open "V" at the corners the box joints could be bent up and the box closed and a good start on the flanges could be done up to the angle permitted. By that time the box would run into the fingers anyway. Then the bends can be finished up by hand forming.
                      Chilliwack BC, Canada

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                      • #26
                        Assuming the photo shows the full size and it's not heavier than 18# steel it will fold up in a box pan just fine remember it will spring enough to get it into position to fold

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                        • #27
                          I would bend the small end flanges first. They are only about 45 degree bends. They can be done in a standard brake by using a mallet instead of the bending leaf. Position the bend line even with the front edge of bending leaf. Gently hammer the flange down to the approximate angle. Now bend the side corners in a B&P. Spring it open and remove from brake. Close the corner seam. Return to B&P and complete large end flange bend.

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                          • #28
                            I think deltap has it! This is how I would do it. With care and appropriate clamping and support you can do nice work with soft mallets. Don't just swing away at it. Gently form the flange a little bit at a time. If you get heavy handed you will stretch the flange and cause a curve in the part.

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                            • #29
                              If this is what is in the first drawing I did it real quick on a Tennsmith box and pan brake. Depending on the dimensions it is no problem. The Z was bent first. I did 90 degrees on the Z flanges since that might be harder. There was no attempt to cut the notches at a 45, just guessing. The ending flange can go on the inside. I put it on the outside for the picture.



                              Last edited by Ridgerunner; 08-03-2016, 06:45 PM. Reason: added on the Z flanges for clarity

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                              • #30
                                The key difference with the original post is that it is tapered. That causes the blank to be somewhat circular, and brings the blank across the bend line of other bends. That is a complicating feature, which affects how much finessing is required.

                                A straight-sided box, as in your pictures , is precisely what a B&P brake is designed to do easily, and is therefore trivial by comparison. The direction of bends can affect how easily the part is made, but the blank is not in general an issue for falling across the bend and interfering with the table.

                                The OP's blank


                                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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