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Sand Bending 3" Tube

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  • Sand Bending 3" Tube

    Hey Guys, no-one in my area has a mandel Bender with 3" dies. I am thinking of welding caps on the exhaust pipes, packing them full of sand and heating and bending. Anyone elese do it this way?
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  • #2
    I have seen this done on smaller should work on the larger stuff too.


    • #3
      Been there done that! Hot bending pipe and coils with homemade mandrels are dying arts to say the least. It was part of our job in my company’s pipe fabrication shop back in the 60’s & 70’s and we did a lot of it.

      1. You won’t want to weld caps on the ends of your tugging, cut out some tapered plugs from a 2x4. Tap the first one in and tape it with duct tap and after filling your tube, tap the last one in making sure there’s little to no air space and tape it over. Never weld the plugs because if your sand isn’t perfectly dry, you’ll build pressure while heating and possible have a serious accident due to the pressure of trapped steam.
      2. Stand the tubing on the end you’ve first plugged and slowly fill it with sand while tapping the tubing wall this compacts the sand and will help minimize flattening of your bend. Don’t just fill the tube and then try to compact it because you can’t. Either fill it by increments (about 2’ at a time), stop and tap or just go slow tapping continually.
      3. There are a couple of methods by which you can hot bend. One is by using a homemade mandrel of a radius of your choosing to bend your tubing around. You can make the mandrel out of a piece of pipe that offers a radius you want or a piece of plate cut in a quarter circle with a piece of ½”x4” bar welded on the edge you’ll bend against. If you haven’t a large flat work area where you can secure the plate mandrel, I’d suggest using a pipe mandrel and make your bends over it. The second method doesn’t use a mandrel and you’ll layout on the tubing wall degreed increments that are you’ll use as witness marks while bending the tube. Both methods require a fixture to hold the tubing and something to pull/bend the tubing once it’s heated to a correct temperature.
      4. Regardless of which method you use, the heating is half the art and half of the skill. Since it’s 3” I say you’ll need to heat the tube in continuous, successive increments and pull/bend it in increments as well. This way you’ll get a nice uniform bend where if you just heat the tubing for some distance and try to bend it it’ll hump up and bend too much in one spot and not enough in another. When you apply the heat use a rosebud not a heating tip and heat the increments until you see only a dull red. When you’ve got that, put some bend into it until you see it slightly stretch in the outside tube wall then stop and move you heat ahead ½ the distance of the heat zone, stop, heat, and repeat the same amount of bend. This is the second part that takes skill.
      5. The other method of bending is you decide how long the outside of your bend want and mark the distance in increments of say 5 degrees on the tubing wall. As an example, if you want to make a 50-degree bend and the outside sweep of the bend you figure should be about 30” long. You’d start putting marks (10) on the tubing from where you want to start the bend 3” apart. This is very important! This tells you exactly how much to bend at a time/heat and how many degrees you should have bent when you move to at each mark! This will give you a very smooth bend if done correctly.
      6. Remember, when you bend anything, the outside wall stretches and the inside compresses! Bend too fast, too cold, too hot, and you’ll flatten the outside and wrinkle the inside.
      It’s pretty tough to try and teach an art that really can’t be taught on paper but by only hands-on experience and a lot of it but hopefully this little bit will get you on track.
      Good luck
      There's no such thing as a welding problem, there are only welding puzzles of assorted sizes!


      • #4
        Sand Bending


        I've used sand a number of times with pretty good success, except the last time. I think I had too much heat. I have not bent anything over 1-1/2" diameter with sand. I'm usually looking for a very tight radius when I use this method. You offered some good suggestions. I've always used silica sand for it's uniform grain size and it's easy to compact. Moisture is not usually a problem. I've always welded caps on both ends. I like your "wood plug" idea. That should give that little extra amount of compaction.


        Good luck with the 3-inch, post pics.

        "Some days you're the dog, some days you're the fire hydrant"


        • #5

          Welcome to the forum. (I have been away, so someone may have already said that).

          Your explaination of sand bending was very interesting to me .... clear, what to watch out for, what to try for and what to avoid. Thank You!

          This type of "been there, done that" knowledge is what makes this such a great forum. Especially about "one man, DIY possible" crafts/skills that are mostly replaced by big industrial stuff.

          Again, Welcome.


          • #6
            Yes, we always used silica sand from our sand blaster supply and used either wooden or aluminum plugs. Because we were pipe fabrication shop for our chemical plant site we generally used full, 20’ lengths of pipe. I forgot to mention that we “listened” for the correct degree of compaction while we were tapping. I added the moisture warning because some folks have been inclined to just go out behind the house to the sand hill and get some sand to use. It’s better/safer to go down to Lowes or Home Depot and buy it by the bag instead!

            I’m glad to hear you’ve had success and as you found out, there are some subtleties about the hot-bending process that affect repetitiveness and that’s why I’ve always considered it as an art form. Even after years of training in the shop many individuals never could get the “feel” it took to make nice uniform bends or coils.
            Ah, the good old days! LOL
            There's no such thing as a welding problem, there are only welding puzzles of assorted sizes!


            • #7
              Dog gone it! I just remembered a way you may be able to bend your 3” tubing mechanically without heat. We used this procedure very infrequently in our shop because we always used NPS pipe and rarely ever used tubing. Once in a great while we’d have to bend a piece of tubing that required a radius that was close to one of our pipe mandrels. Do any of your contacts have a 3” pipe bender? Maybe somebody has a 3” conduit bender? If any do, you may be able to use it to bend your 3” tubing. What you will need is a piece of 3” sch 40 PE or HDPE plastic pipe the approximate length of your bend. Split the plastic pipe and use it as an external shim (sleeve) around your 3” tubing. It should wind up close enough to 3-1/2” OD to work in a 3” pipe mandrel or bending machine because the plastic will be somewhat forgiving if the bender has a fixed follower. This is a non-heated bending operation (you’ll melt the PE) but I think you’ll still have to fill it with sand depending on the 3” mandrel’s radius.
              Good Luck
              There's no such thing as a welding problem, there are only welding puzzles of assorted sizes!


              • #8
                Well, yer all too dang far from me to use my benders, or my buddy's exhaust bender/pretzel twister.
                Since this started out mentioning exhaust tubing, a subject I'm unfortunately conversant with, let me suggest you'll be a lot better off buying the bends and welding them up. The current crop of exhaust tubing leaves a lot to be desired in ductility when bent.