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  • Salt for bending

    If I remember correctly Evan mentioned using salt to fill tubes when bending. If so what kind of salt and any other tecniques that are important. I am wanting to bend some thinwall brass tubing and keep the cross section as pure as possible.

    BTW it is Evan's fault that I have this problem. I read about all the joys of "retirement" and watched him complete about a million large tasks in the shortest of time. So after 42 years in the classroom as a Machine shop/Drafting/CAD/CAM instructor I too retired. Where is all the "free time" to get my stuff done. The "honey Do" list looks like an encylopedia and the "lets do something" list is just as long. I envisioned quiet time in my shop building a set of street clock works followed by a beam type steam engine ect.

    Actually a great big "Thank You Evan" as I now have time to do the "Honey Do's" as they should be done rather than "quick and dirty's" because of the length of a weekend and the demands of employment.

  • #2
    Anything granular that can be packed tight will work for a bending medium. Makers of musical instruments use rosin for bending brass tube for trumpets etc. Melt out the rosin and they have a nice bend. Then they jig the bend and force steel balls through it to round it back up.

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    • #3
      No expert here but do realize that this is most probably an "art" and could get extremely involved with size/compression/and shape of the material at use, for instance i would imagine salt and sand as two different things as the salt would more redidly give way to turning into a powder, could also imagine using H20 and sealing ends off before bending would give results anywhere from a broken tube to just what you wanted depending on what your trying to bend in the first place... round steel bee-bee's, lead shot, you get the idea, Now for Evan to post his already bookmarked website on the subject

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      • #4
        Originally posted by Forrest Addy
        Then they jig the bend and force steel balls through it to round it back up.

        I just caught that,, one example; enter formula V race engines where they are held down to stock parts in just about every catagory, along with stock compression and everything else, but you can heavily modify many of the stock parts, like the intake manifold, they extrude hone them (force an abrasive/clay compound through them) they acid etch them, they do about anything they can to open up the I.D. and make them flow as good as possible --------- some guys spend an ungodly amount of time on them, get them to flow better on a flow bench better than any of their other previously modified manifolds including running steel balls through them for the final touch to remove any little dents or tight spots ----------- Bolt them on the race car and go to test on the track - hit turn #1 and have to lift (de-accel) only to suck a hole in the manifold because the metal was so thin

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        • #5
          Salt for bending is a very old trick. It works well because of the cubic shape of the crystals which prevents them from sliding around under compression. Other granular materials will work but many are rounded (sand) and won't hold shape as well. The other major benefit is that salt can be washed out with water ensuring that absolutely not one grain of grit remains.
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          • #6
            We used to use salt for making copper tube induction coils at a place I once worked. The tube was flattened somewhat through the middle section leaving the ends untouched for connectors. Then the tube was filled with salt and formed into the required flat coil (tube on edge). When the coil was done they were thrown in a tank of hot water for a time with occasional agitation to get the salt dissolved and out. It always worked.
            .
            "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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            • #7
              I've seen ice used to fill a tubular handrail for bending.

              Sheetmetal, and precision assembly guys at NASA did this.

              Just let it sit at room temp for a while and be done.


              Also seen of teflon bar inserted, and pulled out when done.

              This was done on plastic pipe with a bit of heat.

              Kap

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              • #8
                PLUMBERS HERE USE A WELL FITTING SPRING FOR bending tube copeer etc.This can be pulled out with a piece of string Alistair
                Please excuse my typing as I have a form of parkinsons disease

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                • #9
                  For bending odd shapes like spouts for silver tea- and coffeepots, you can fill them with lead. After bending, just melt out the lead. Be careful though... ANY lead left will burn holes right through your creation when hardsoldering it onto something.
                  The residual lead willl alloy with the other metal and very locally lower the meltingpoint.
                  To prevent this you usually coat the inside of the tube, spout, ... with yellow ochre before pouring in the lead.
                  This trick is very well described by Rupert finegold and William Seitz in 'Silversmithing'. Really, really, really great book!

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                  • #10
                    Salt crystals are shaped like cubes. The theory of using cubes in bending can be visualized by stuffing a bunch of shoe boxes in a large water pipe and pushing them all to the other end. They slide along like box cars, all neatly aligned. Any other shape will cause interlocking and binding and finally a jam because they will push outward as well as in line with the pipe.

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                    • #11
                      Step',

                      Some tube benders have formulas using the wall thickness and OD of tube as important parameters to determine the difficulty in getting a nice bend.

                      One such formula says that if the ratio of the wall to OD is .07 or less internal support of some kind is needed. For instance: 1/16" wall, 2" OD would be .062/2=.031. That would need some internal support. Of course, these formulas assume a good set of bending dies.

                      What are your numbers for wall and OD? And what kind do bending dies do you have?

                      I'm no fan of packing sand or salt into a tube and sealing the ends, a hassle. Cerrobend (low melting point alloy) is good. Freezing the tube with water is good too, don't freeze super hard though. Whatever method, pushing ball through is a final step.

                      IMO, the bending dies are the most important factor. Without good dies you're asking for problems. Some people try to bend with the cheapo import pipe benders which don't do much of a job.

                      BTW, some one is sure to ding me on the 2" OD example I used. Exhaust pipe of that size is bent all the time without internal support. But, exhaust bends aren't usually very good unless an internal mandrel is used. Plus some exhaust dies are purposely made to wrinkle the inside radius so the aluminized coating isn't thinned.

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                      • #12
                        Originally posted by dp
                        Salt crystals are shaped like cubes. The theory of using cubes in bending can be visualized by stuffing a bunch of shoe boxes in a large water pipe and pushing them all to the other end. They slide along like box cars, all neatly aligned. Any other shape will cause interlocking and binding and finally a jam because they will push outward as well as in line with the pipe.

                        brilliant analogy DP, and very true to some degree but im wondering what happens along the inner and outer turns with this as the inboard turn gets shorter and the outer gets longer, do the "boxcars" simply "swap rails" whilst under pressure? now that you mention it --- I wonder about all kinds of shapes including triangles, but the almighty sphere might be tough to beat in certain aplications as it is influenced in all directions is it not?
                        This is a very interesting topic as with the different shapes sizes and compounds along with the different material tubes and thickness and even shapes (square tubing) the posibilities are endless...

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                        • #13
                          Originally posted by DR
                          I'm no fan of packing sand or salt into a tube and sealing the ends, a hassle. Cerrobend (low melting point alloy) is good. Freezing the tube with water is good too, don't freeze super hard though. Whatever method, pushing ball through is a final step.
                          How do you force the ball around a corner? Do you press one ball as far along as possible with something like a Porta-Power, and then follow with enough balls to make the curve?
                          "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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                          • #14
                            What kind of salt?

                            So the distaff side of the household asked me"What kind of salt?" I replied "the salty tasting kind". So I got the long long lecture on Kosher Salt and Sea Salt and Iodized Salt followed with the "Why" question, hence the question that started this post.

                            As to benders I have a good bender that is capable of 1-1/4 pipe and I have the dies for the desired 1 inch tubing.

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                            • #15
                              Salt crystals are shaped like cubes. The theory of using cubes in bending can be visualized by stuffing a bunch of shoe boxes in a large water pipe and pushing them all to the other end. They slide along like box cars, all neatly aligned. Any other shape will cause interlocking and binding and finally a jam because they will push outward as well as in line with the pipe.
                              While it sounds right that isn't what happens. Salt crystals are indeed cubes. Cubes however are not self organizing like spheres are. What happens is the salt crystals end up randomly arranged and resist movement in any direction including the easy ones.

                              This can be shown by taking a tube and fastening a light weight piece of material such as a tissue on one end with a rubber band. It should be just secure enough to hold the tube full of salt for six inches or so. Then fill the tube with that much salt. Take a stick or similar object and try to push the tissue off the end of the tube by applying pressure to the top of the salt column. It's impossible as the random alignment of the salt crystals ends up transferring all of the force to the sides of the tube causing the crystals to lock in place.
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