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  • Scaling up project dimensions

    I found a project I'd like to build (JRW sheet metal brake) but it's a bit lighter than I'd like.
    Would scaling up the component sizes by a percentage factor be a successful way to do this?
    Len

  • #2
    I'm no engineer but I would think scaling to the force required for a bend would be a better way to ensure performance. Take for example, (it's an example...) if it took 1 ton to put a 90° bend in 1/8" mild steel, that means that 2 tons would be sufficient to do the same bend in 1/4 mild steel. The same consideration needs to be applied to large increases in length.

    Like I said...not and engineer, and my advise is worth what you paid for it.
    My recommendation?

    No matter what I tell you, get a second opinion.

    Comment


    • #3
      I think the idea is fine in principle. But when it comes to doing so it won't be as easy as you might think. First off material only comes in given sizes. Second is that if you alter those sizes you'll also need to alter the parts that connect to them to adjust for the size changes. So basically you either re-engineer it on the plan and make a whole new plan or you do the re-engineering on the fly in the shop. And finally if the goal is to size it up by, say, 50% and use 50% larger sizes, if they are available, then the other issue is that the metal does not flex in a scale like manner. If you enlarge the whole machine then it's quite possible that you need to increase the size of the material by more than the scale factor to achieve the proper stiffness for the middle of the span of the parts.

      Tony, you posted above;

      Take for example, (it's an example...) if it took 1 ton to put a 90° bend in 1/8" mild steel, that means that 2 tons would be sufficient to do the same bend in 1/4 mild steel.
      But that is not the case. The 1/4" material is more than twice the stiffness and strength of the 1/8". The bending strength goes up by the square of the increase in thickness. So two pieces of materials of the same size but one twice as thick will see the thicker one being four times as strong. Put a piece of 1/8 x 1 in the vise and bend it. Then repeat with some 1/4 x 1. WAY more than double the effort is needed.
      Chilliwack BC, Canada

      Comment


      • #4
        I'm not sure what you mean by "lighter".

        If you mean it is not strong enough to do the work it should, then if you just scale up all the dimensions will only make it more flimsy. What is really needed is to "beef up" the parts at their existing size so they can do the work.

        But if you mean that it does not have a large enough work envelope and you need to work on larger parts, then scaling up MAY work. But you need to consider that as size goes up, the need for stiffness increases. So if you scale up a 12" brake into a 36" brake, a 3X increase in the work envelope, you may need to increase some of the dimensions by more than 3X. This is called engineering. It can be done with a lot of math calculations or it can be "seat of the pants" engineering. "Cut and try." or whatever method you choose.

        The common idea here is that if you just scale up all the dimensions by the same factor, the machine that you wind up with will be less likely to be able to do the intended work, even on the same gauge of metal. There is a fundamental principle at work here. The simplest example of it is a simple, horizontal beam that is supported at both ends. Assume you have an I beam that bridges a certain span. This could be a bridge or a roof or whatever. Now if you just scale up that I beam, some would expect it to get stronger. But if you include all three dimensions in that scaling, then the length also increases. The strength of that I beam will increase with the cross sectional area which will be the second power of the scale factor. But the weight of the beam will increase by the third power of the same scale factor. So the weight of the beam increases faster than it's strength. This is a case of diminishing returns and sooner or later you will reach a point where the beam will fail/sag under it's own weight. So there are limits on simple up-scaling.

        You can probably use the general design of the original machine, but you should consider the needs of each part individually. Many of them will need to have their cross section increased.
        Paul A.
        SE Texas

        Make it fit.
        You can't win and there IS a penalty for trying!

        Comment


        • #5
          Originally posted by BCRider View Post
          ...But that is not the case. The 1/4" material is more than twice the stiffness and strength of the 1/8". The bending strength goes up by the square of the increase in thickness. So two pieces of materials of the same size but one twice as thick will see the thicker one being four times as strong. Put a piece of 1/8 x 1 in the vise and bend it. Then repeat with some 1/4 x 1. WAY more than double the effort is needed...
          Exactly! What I'd be doing is looking at machines of the capacity you need and designing around that. Remember that virtually
          all of the cheaper import brakes are built lighter than what you really need to do the job--they will flex and give more than is
          acceptable unless you're working with really light material. Mass is important in these machines and a lot of the lighter ones
          simply don't have it...
          Keith
          __________________________
          Just one project too many--that's what finally got him...

          Comment


          • #6
            HERE IS A LINK to the brake I think you mean.

            If you compare the design to the larger ones I think you'll agree that larger brakes have more stuff on them to enhance their stiffness. Like the truss rods that triangulate off the pieces to enhance their stiffness. So I think you'd want to do more than just scale up the JRW design. To handle larger work and particularly heavier gauge steel it would need a lot of major changes that would make it similar to a proper commercial brake of the size you're after.
            Chilliwack BC, Canada

            Comment


            • #7
              Here's a PDF of the plans; http://www.homemetalshopclub.org/pro...etal_brake.pdf

              What I'm thinking is if I add, say, 25% to every size called out it should be able to handle 18 gauge, full width, with
              no problem.
              As it is I think capacity is only 20 or 22 gauge.
              Len

              Comment


              • #8
                What I'm seeing is all steel plate. And with the plates sitting "flat" at that. But the bigger units that are strong enough to do things like 18Ga for full width tend to use box and angle sections along with those V trusses to aid with stiffness. Like THIS ONE

                In searching for examples I also found THIS PAGE on a DIY metal brake. Haven't watched it yet but it may be more in tune with what you want.
                Chilliwack BC, Canada

                Comment


                • #9
                  That scaling and stiffness works for machine parts also.

                  If you double the depth of a beam, without changing thickness, you get an increase of stiffness. If you do it proportionately in depth, width and thickness, you increase by a considerably larger factor.

                  So a spindle, for instance, that is increased proportionately to 3x the OD, would be something on the order of 27 times stiffer than the original, taking into account the increase in basic diameter, and the increase in material area. A cube factor.

                  So the bender example, if you just make it take wider material, with no change to any other dimension, you lose stiffness. If you make it proportionately larger in all dimensions, then you will get an increase in capacity to go along with the size.
                  1601

                  Keep eye on ball.
                  Hashim Khan

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                  • #10
                    Ahhh, I didnt read any of the other posts. Just yours and I would say when scaling up you have to scale in a logarithmic "pattern" and not linear.

                    That means you have to know the exact weight and needs at every stage of the up scaling. If that makes any sense.

                    Figure out what you need and build that. You could prolly incorporate all the details of the brake you want too. Dont make it flimsy. JR
                    My old yahoo group. Bridgeport Mill Group

                    https://groups.yahoo.com/neo/groups/...port_mill/info

                    Comment


                    • #11
                      Originally posted by BCRider View Post
                      What I'm seeing is all steel plate. And with the plates sitting "flat" at that. But the bigger units that are strong enough to do things like 18Ga for full width tend to use box and angle sections along with those V trusses to aid with stiffness. Like THIS ONE

                      In searching for examples I also found THIS PAGE on a DIY metal brake. Haven't watched it yet but it may be more in tune with what you want.
                      Yeah, I've searched for hours and turned up as many ads and plans as can be found on the web.
                      Most are making some really outrageous claims for capacity.
                      Of course, when I wasn't interested, Craig's List was lousy with them...decent ones too.
                      Now?
                      Broken, cracked, missing fingers, etc.
                      Len

                      Comment


                      • #12
                        Originally posted by J Tiers View Post
                        If you make it proportionately larger in all dimensions, then you will get an increase in capacity to go along with the size.
                        That's what I'm looking for.
                        Thanks.
                        Len

                        Comment


                        • #13
                          I don't mean to pick on Tony. I just happen to have researched this stuff recently.

                          Rigidity is proportional to the cube of the thickness. A 1/4" plate will need 8x as much force to bend as will a 1/8" sheet of the same material.

                          Longer levers to get more force mean the levers have to be thicker - deflection (bending) of the lever is proportional to an exponent of the length.

                          Another route... assuming the brake (and your project) can handle contact with higher temperature, just heat the sheet or plate to incandescence prior to bending.

                          Comment


                          • #14
                            Originally posted by Lee Cordochorea View Post
                            ... Another route... assuming the brake (and your project) can handle contact with higher temperature, just heat the sheet or plate to incandescence prior to bending.
                            But then your pencil mark that shows where to make the bend may no longer be visible.
                            Location: Long Island, N.Y.

                            Comment


                            • #15
                              Originally posted by Lee Cordochorea View Post
                              Another route... assuming the brake (and your project) can handle contact with higher temperature, just heat the sheet or plate to incandescence prior to bending.
                              have you tried that?

                              Originally posted by QSIMDO View Post
                              What I'm thinking is if I add, say, 25% to every size called out it should be able to handle 18 gauge, full width, with
                              no problem.
                              .
                              If the original could handle 22g and you want 18g.....that's a 60% increase in force you're going to need to apply - assuming the 22g was realistic in the first place. If you want the brake to have the same stiffness as the prototype would at 22, you going need the parts it be several times the size not 25% because of the exponential nature of stiffness, assuming the same bend length.

                              What are you wanting to bend? Bending metal takes a lot of force, just look at the size and weight of commercial brake (not that BS often offered up on offshore hobby stuff) ratings. imo whats practical is a very light folding style brake (I make the finger brake below) or a hydraulic press with dies. Unless it is a constant requirement, I'd consider outsourcing the odd job that went outside of the work envelope of those two

                              Last edited by Mcgyver; 10-28-2018, 10:40 AM.
                              in Toronto Ontario - where are you?

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