24 Replies Latest reply on Sep 21, 2011 7:29 PM by Bernie Daraz

    Joggle or Offset Bend Allowance? (new post, still trying!)

    Bernie Daraz

      I had an earlier post in this regard, to me there is no way to 'tell' SW your tried and true bend allowance for a joggle or offset bend. When I mention tried and true, it has been actually tested in the same material, grain direction, width or length of bend and tooling. In my case I have a list of them that has been built over 37 years in this business, for both bend allowances and bend deductions.

       

      So now I'm doing the design and I want to provide models that flatten and can be imported into the vendors systems without tedious programming and modifications. This joggle allowance in SW is totally messed up and virtually incorrect. Today I was working on a part with a simple joggle and I look at my list, it should have a bend allowance of .010 for a .040 offset in .036 steel. No way can I enter that directly! I could layout this part using scribe lines faster!

       

      Then it occurs to me that using "fix projected length" and allow me to enter a known allowance there and I'm done. But it doesn't work that way! Anyone in this business for a decent amount of time knows that a joggle shortens the blank. We're not concerned about the height of the joggle (so much) as that is controlled by the depth of penetration of the tooling. We are only concerned with the amount the blank shortens, that is the joggle allowance.

       

      A k-factor cannot be used because it is not consistant even in the same material. A k-factor would be one number for a joggle that is 1/16" deep and then a totally different number for it if the joggle depth was 3/32". We do send out parts that have two joggles in the middle area and mounting holes on the ends that need to be within .010 after bending.

       

      Think about it, if your comment is that it's close enough for us, it most likely wouldn't be if you were paying the professionals to do it. If your prints had decent tolerences on them you would be able to reject the parts. If your vendors are asking for fully dimensioned prints, your SW files are doing them no good. OK, they do use that excuse to get a few more delivery days too if they're running late or have already messed up your parts once.

       

      My two cents worth of venting! I see it hasn't been fixed in 2012 beta, so far.

       

      I would love to hear from someone who has a repeatable and accurate method. (play the theme from Mission:Impossible here! LOL!)

        • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
          John Stoltzfus

          Good morning Bernie,

           

          Interesting Post!!

           

          There are so many factors when it comes to sheet metal forming it can make your head spin.  You have got to know either a good operator or a good job shop to get the tolerances that you speak of. 

           

          The changing factors are, Thickness, Length, Top Die, Bottom Die, Combination of Top & Bottom Die, Material, Material Grain, Temperature, Moisture, Human Error and it could be more!!!!!

           

           

          You mention that you have a list of bend calculation/bend allowances, that was compiled for 37 years there are a lot of people that would like a peak at that list, I am sure to be one of them.

           

          One option that you can do in SW is create a Bend Table which includes your bend allowance and k factor.  Once your list is compiled in a Bend Table you should be able to mouse click the right information before you can scribe the plate. 

           

          Could you send me your list so I can get it in a Bend Table format???

           

          Later,

           

          John

            • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
              Bernie Daraz

              Good Morning John,

               

              My first thought is appreciative. I'm appreciative of your positive response, I didn't intend for my post to go over badly or even insulting.

               

              I understand the variables you speak of and know them very well. I have been doing the layout, bending, welding, rapairing of rejects etc., for more than 37 years. I speak expressly from actual experience, not school taught and trying to make it work in the field. I've done it all in the field and made those tolerances as required from high end customers including IBM and Pitney Bowes.

               

              To say that sheet metal should just be close means you're not trying or you don't have the talent. I have worked on the floor as well as in the programming department in a number of shops, what worked as a bend deduction in one shop just doesn't work in another. Is one wrong, no. That's why SW needs to embrace the fact that there are many methods and some inescapable ones.

               

              Just last night I was trying to input a known bend allowance to a joggle and the system is telling me it won't work. Granted SW is now at it's 20th release and is a very respectable piece of software and a valuable tool, my tool should be an extension of me. It shouldn't act as a worn screwdriver as is the case in joggle bends. It shouldn't limit me and my experience and my definitive knowledge and experience. Just because it seems that mathematically it won't work doesn't mean it shouldn't.

               

              That said, and I'm not really done, I would be glad to send you a copy of the lists. You should realize that it may not work for your shop for the same reasons you mentioned above. It might need tweaking.

               

              I fully intend to offer these on a wider basis as I will be creating a blog very soon.

               

              Regards and no offense intended of course, to all.

              Bernie

                • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                  John Stoltzfus

                  Good morning Bernie,

                   

                  Your post didn't come across as bad or insulting.

                   

                  I have done some sheet metal forming and you have around 11 years over me in that area.  I have also started on the shop floor so I know what your talking about. 

                   

                  Your list would be hard pressed to implement in our shop and my general feeling is we don't have a press operator that could comprehend what your saying.  The reason I would like the list is so I can start to establish parameters. 

                   

                  There is also a big difference in Air Bending or Punch Forming a part

                   

                  Thank you,

                   

                  John

                  • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                    Erik Bilello

                    Bernie,

                     

                    To defend "school teachin" and "book lernin".  When I was in school we were taught that formulas and tables were acceptable for general layout calculations, but that when you need high accuracy you should always make test bends with the correct material, tooling, bend angle, etc. and then calculate true bend allowances for your layout.

                     

                    That said, I agree with you that SolidWorks needs a better way to allow joggle allowance (shrink, stretch or whatever your shop guys like to call it) to be entered.  A joggle is not just two little bends right next to each other and shouldn't be calculated as if it were.

                      • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                        Bernie Daraz

                        Erik,

                         

                        Yes, I agree too!

                         

                        In no way did I intend to assualt anyone or even schooling or books. Many if not most would know that a joggle is not two bends close to one another. Your addition of the terms, shrink or stretch is a valuable contribution to this conversation.

                         

                        Bernie

                          • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                            Erik Bilello

                            Bernie,

                             

                            No insult taken.  Note I said "when I was in school"  I don't know what they teach today.  Best we stay away from the whole argument about the disconnect between the average person (and lots of engineers and designers) and how things are made these days.

                            I referred to the joggle as two bends because I recall that's how SW calculates it when left to it's own devices.  Therefore, somebody somewhere once thought that was how a joggle worked.  Or close enough.

                             

                            As for terms, it seems like every shop has it's own terminology to describe things.  I think it's based on how they visualize what's happening when the metal is formed with a dose of "tribal knowledge" thrown in.  Are you starting with the formed dimensions and developing a flat pattern or flat pattern to formed part, calculate from the ID or the OD, bend deduction or X-factor . .  .?  Practically everyone has perfectly good reasons why their method is best.  But as long as the results are good I don't care what language they speak.

                    • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                      Daymon Hoffman

                      Hi Bernie,

                       

                      All i can say is... i feel your pain and i hear ya! 

                      • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                        Toby Robinson

                        Hi Bernie

                         

                        If you uncheck use default radius and use .001 solidworks will let you make the .040 offset. Then use a bend deduction of .005. That should make the flat with in .002 of what it should be. You should be able to adjust the bend deduction to make the flat what you want.

                         

                        Toby

                          • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                            Bernie Daraz

                            Toby,

                             

                            You are right and I do exactly that. My issue though is with the fact that now I have a working model with the correct bend allowance but my vendor wants to update it to a slightly different one. He cannot just change it to .008 (total) as it will not correctly relate to his actual working allowance.

                             

                            Without this ability my files are useless (to the vendor) and I'll still need to provide fully dimensioned drawings. Why isn't everyone adopting CAD? I know.

                             

                            After I complete a model I go back and check a few flat dimensions to insure the proper application of the bend deductions and allowances. I could draw and model almost anything but I want to insure my models are usuable across the spectrum. In all cases I am not afraid to share my models, they will work for you. Put a joggle in there and I'm not. Remember, I've actually done this from scribed lines to today, I know what works. To have a tool that doesn't allow me to apply my knowledge and talent is a limiting factor, both in talent and production.

                             

                            Thanks Daymon! Someday I hope!

                             

                            If you've ever heard your vendor say "I still have to change a few bend radii here and a few deductions..." and you panic for a second, you know something isn't perfect. If you're sure you're 'good to go' because of the print, who is actually doing the workaround? When you make usuable models your vendors will love you and you'll get better prices and quality. Just because its easier.

                             

                            Bernie

                              • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                John Stoltzfus

                                Good afternoon Bernie,

                                 

                                In our area there are very few businesses that are setup for those tight tolerances, most of it comes down to "Ah! it's not that important, just make the hole bigger so it fits" 

                                 

                                I can now appreciate guys that I worked with in the early 1990's.  There were a few guys that worked for Haan Fire Truck company and these guys knew sheet metal.

                                 

                                One thing that you mentioned is:

                                 

                                To have a tool that doesn't allow me to apply my knowledge and talent is a limiting factor, both in talent and production.

                                 

                                I think SW is the tool for sheet metal, it's just that it may take more to set up the parameters for what you do.  The neat thing about using SW you can take a systemic approach.

                                 

                                Keep up the conversation and let me know when your blog is up and running,

                                 

                                Later,

                                 

                                John

                            • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                              Toby Robinson

                              When I was doing sheet metal 95% of the time whenever we got someone else’s sheet metal solid model I would end up recreating it from scratch or have to change some settings to get it to work for are shop.


                              I don’t think you can get your models to work across the spectrum because every shop uses different bend deductions. You can work with your venders to set up what settings they use. The problem with that is if you send the same part to two different venders you have to save the part with different settings for each vender.

                              I set are settings to work for are shop. If we had anything made by someone else I would send them what I wanted the finished part to look like. If they asked for the model I would send them it but tell them they might have to adjust some of the settings.

                                • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                  Bernie Daraz

                                  Toby,

                                   

                                  I can tell we would have gotten along great doing business. You show a theme of cooperation that is not often matched in the real world.

                                   

                                  The idea is to offer an intelligent, correct and editable model so any individual vendor can apply their own values. That is what this post started with, my known and accurate values and of course theirs now. If SW requires me to fudge a value to achieve a good result then that model is incorrect.

                                   

                                  I will state that I have learned about as much from good modeling practices as seeing bad and correcting them. All I'm asking for is SW to allow me to apply these directly. How long would any of us like it if SW didn't allow us to make good models?

                                   

                                  I always will try, but like everyone else, I'm not perfect. I will continue to strive for that goal though.

                                   

                                  Bernie

                                    • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                      John Stoltzfus

                                      Good afternoon Bernie,

                                       

                                      It takes debate and discussion in progression so all is good, do you use bend tables??  Not saying you have to but like Toby mentioned below you would be able to set up a bend table according to your vendor.  I agree with what you say about getting the part modeled correctly, because we need to be able to establish a quality level, so that it fits when it goes out the door.

                                       

                                      Even creating different bend tables for the different vendors won't answer all of your issues, but I would think it would do a lot for you.  The important part is knowing what your vendor can do and what for dies he has.

                                       

                                      I would say that the die selection from one shop to another makes a huge difference, also if the press is mechanical or hydraulic.

                                       

                                      Good stuff Bernie, Lot of fun,

                                       

                                      John

                                        • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                          Bernie Daraz

                                          John,

                                           

                                          I agree! This is spirited to say the least. In one sense it pisses me off too, I will try my best not to let my 'intensity' anger anyone.

                                           

                                          Tables would do it but I really believe the issue is that SW will not accept the value in any case. This causes me concern going down the road. There are the differences you mention and also what about (inexcusable) lazyness on the part of the brake operator? "I thought I could "air bend" the .093 with my .062 setup."

                                           

                                          I didn't want to do all this work myself, I wanted to suggest the changes that would help us all. Hell, they could put on my tombstone, "He got SW to make joggles work!" LOL! I hope we all can be a part of making something great even better. We all will gain.

                                           

                                          Yes, this is fun! Thanks for being a part of it.

                                          Bernie

                                            • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                              John Stoltzfus

                                              Good afternoon Bernie,

                                               

                                              The headstone might even say "Here Lies Bernie"

                                               

                                              I heard ya on all the rest,

                                               

                                              I would like to be a mouse if you would fax or email your drawings to our shop

                                               

                                              I don't think it's nice to bang on our guys here, it's just that they aren't used to it and we aren't making Swiss watches here and the quality that goes out the door has worked for these guys many years, so I just need to shut up from here.

                                               

                                              Later,

                                               

                                              John

                                                • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                                  Bernie Daraz

                                                  Thanks John!

                                                   

                                                  Some of this I'm basing on a project we did with a firm back in 2000. No joggles but the project was paperless except for some bend dimensions. None of the hole sizes or positions were checked at inspection. The drawings showed the standard 3 views with bend dimensions only.

                                                   

                                                  There were only two firms invited to this attempt and I loved the challenge. Incidentially it was done in Pro-E 2001. By the way, we delivered on time and no rejects. The firm later bounced off saying the entire attempt was a waste of time and money. They sent me and the programmer from the other shop to Pro-E training and supplied the computers and software to both of us.

                                                   

                                                  I sold the computer more than a few years back. If you make the drawings as well as the models you probably know it takes a more than reasonable amount of time to detail the drawings. This eliminated much of that tedious labor. SW has announced some advances in the auto-dimensioning of drawings and I look forward to checking those out.

                                                   

                                                  I can appreciate you comment about the "Swiss watches". But if something doesn't start out right how can it possibly come out right? Also, not to bang in the guys, I was one of them! They have to save the inaccurate jobs, they do it and I've done it. Again, I learn from my mistakes as well as anyone elses.

                                                   

                                                  I'm not a pro-golfer, football or tennis player. But I still consider myself a professional.If you ask me what's wrong I'll tell you from my point of view. I would see if your guys have any suggestions as to how to improve. Better yet, if you see one of them with a hacksaw adding a bend relief, find out how you missed that. I'm sure they would be happy to tell you.

                                                   

                                                  It's all good!

                                                  Bernie

                                                    • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                                      John Stoltzfus

                                                      Good afternoon Bernie,

                                                       

                                                      You mention :

                                                       

                                                      SW has announced some advances in the auto-dimensioning of drawings and I look forward to checking those out.

                                                       

                                                      My comment on that is just be careful how far you take the automatic stuff, I guess I have seen to many things blow up for me because of how I started the model and made changes according.

                                                       

                                                      The biggest challenge for me has been and always will be "Design Intent" and if your initial approach is started on the wrong foot it doesn't matter how many automated gizmos you have.  I know SW puts a lot of hype into the linear change thing but say you go from a round to square and then what everything from that change will come a crashing down. 

                                                       

                                                      For me I would approach your application this way,

                                                       

                                                      Get the model as close as possible and then when you dimension your drawing provide tolerances on all the pertinent dimensions, however I think your issue is more what you put into the bend allowance block.

                                                       

                                                      That made me think of another comment I heard years ago;  "If you have too many issues cancel your subscription" or "If you can't get over it grease yourself and slide under it"

                                                       

                                                      I hear your vents and through discussion a product does get better,

                                                       

                                                      Later,

                                                       

                                                      John

                                          • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                            Toby Robinson

                                            Hi Bernie

                                            I was thinking about it some more and John might be onto something with bend tables. You can set up different bend tables for the different venders you have. That should allow you to easily create the different flats for you venders. I have not used design table so not 100% sure if it will work.

                                            For solidworks may be put in an enhancement request. I’m thinking of an option to turn on so solidworks will calculate the jog as one bend and not two 90 degree bends. Since solidworks will let you make a 2” jog I thing that is why it calculates it like that.

                                            The only other thing I can think of is maybe some type of form feature that will let you enter a bend deduction

                                              • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                                Bernie Daraz

                                                Toby,

                                                 

                                                I just relied to John regarding the bend tables, please see that reply. I'm sure you were notified by email that it was posted.

                                                 

                                                I love the form feature, although it does not show the 'thinning' that occurs on deeper forms. I can also design a tool that will end up tearing a hole through the material. To have the form feature use a bend deduction, stretch or shrink, is way more than I feel that I can ask for now. I believe you are correct too, "that why SW allows you to make a 2" jog".

                                                 

                                                I think I use a jog bend up to about 6 times the material thickness now, then I use separate bends in my models. I try to go for the common fractions in my offset dimensions knowing that a more accurate depth change is likely achievable with the next 'deeper' jog tool set to the proper penetration.

                                                 

                                                Although I've never checked or otherwise verified this, I've been told by our special tooling manufacturers that joggle tools require 4 times the force or tonnage to make the two bends. Not twice as might be thought. That is where I believe the neutral axis does not take a consistant offset path with regard to the point of no stretch or shrinkage. Where it might on a more normal bend, such as a .062 radius in 16 gage steel.

                                                 

                                                Since it would extremely difficult (not impossible) to have SW calculate that path I would rather have SW allow me to input my figure.

                                                 

                                                Bernie

                                                  • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                                    Toby Robinson

                                                    Bernie

                                                    Do you know who your VAR is if you have one? I would send this to them so they can send it to solidworks as a problem.

                                                     

                                                    For right now the only thing you can do is change the bend radius so solidworks will not error on you and then fudge the bend deduction to get the flat pattern correct that you have to calculate by hand using figures that you know work.

                                                     

                                                    I guess start adding to your list that you have of what settings you have to use in the computer to get it to work in the real world.

                                                      • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                                        Bernie Daraz

                                                        Toby,

                                                         

                                                        Obviously it's time to renew and upgrade. They will be hearing this after I give some time for 2012 to shake out. I'm not the earliest adopter!

                                                         

                                                        I do the changing and fudging now, it's more work for me! OK, that part is definately selfish.

                                                         

                                                        Bernie

                                                          • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                                            Toby Robinson

                                                            Not only is it more work and a pain it also increases the odds of making a mistake. It’s easy to forget that on a jog you have to use ½ of the bend deduction. In my case ½ of the bend deduction worked most of the time.

                                                              • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                                                Bernie Daraz

                                                                Toby,

                                                                 

                                                                That's an interesting concept! For me and the last 4 places (jobs) it's been a fixed value (previously tested of course) applied from a list maintained in Notepad or it's equivalent.

                                                                 

                                                                Next time you do a jog bend in SW don't check "fix length" or whatever the check box is called. If you watch the preview as the model updates the bent flange shrinks. My point here is that the shrinkage is the amount of bend allowance. If I could input an amount that causes the flange to have the length "fixed" this issue with SW is solved.

                                                                 

                                                                I refer to bend alloawance as an amount I add to a blank when figuring a flat. A bend deduction is an amount subtracted. Both have important distinctions and their use is dependant on shop practices. Of course having either as a known value some grade school math will give you the other one.

                                                                 

                                                                I'm sure there was a point depending on the depth of the offset where the formula stopped working well. It's also a coincidence that 1/2 of the material thickness works as a bend deuction for hem bends. The kind that are bent with an acute (knife) die and flattened so there is essesntially no gap.

                                                                 

                                                                Thanks for your comment!

                                                                Bernie

                                                      • Re: Joggle or Offset Bend Allowance? (new post, still trying!)
                                                        Bernie Daraz

                                                        I now see there is a post for a similar issue in regards to hem bends. Why fudge anything? If SW would aknowledge and change the method for jogs, the same practice would apply to hems. Without insulting the programmers of SW, it looks easy to me!