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Thread: Mandrel bendign tube and pipe on the cheap.

  1. #1
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    Mandrel bending tube and pipe on the cheap.

    Some time ago I mentioned ice mandrel bending and it seemed few were aware of it. I'm working on a project that needs 56 @ 30* elbows bent, so I got a new bender for Roque fab and got to work. With the ice mandrel inside, I only got 0.044" of wall collapse, just a tad over 1 mm. That's very near a true mandrel bend. Without the Ice mandrel I was measuring about 4 mm, or about 0.160", This is a wall collapse reduction/improvement of 400%.

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    You want the pipe slightly over full, this increases the inside pressure of the ice, and limits ice shift. I capped one end by welding on a scrap, and used another scrap for the top with a hole in it for filling. If you leave this end open, the ice just shifts out the open end. This keeps the mandrel in place and still makes it easy to fill.

    Prior I did try just water with both ends sealed. I uses a pipe plug in one end so I could get the water full to the brim with zero air, and then plugged it. Even though water is incompressible, being a fluid allowed it to apply internal pressure evenly across the entire pipe surface. THis meant the wall collapse was still allowed because it only had a few hundred PSI pushing back on the inside. Because the ice can't move and spread the pressure across the entire internal surface of the pipe, it contained the force to the walls under bend.

    I tried sand earlier and it still collapsed more than I was willing to accept.

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    One trick is to use about a tablespoon of dish soap per quart of ice water, this allows the ice to fracture and slip between the grains into a fine texture similar to sand, rather than large blocks of ice that can cause a stress riser in the pipe during bending, which can cause pipe failure mid-bend.

    Also, I found even a little meltage drastically reduces effectiveness, it must be all frozen. The melted ice water will just displace and move out of the bend area, allowing shift and collapse inside the bend area. The bending will cause some meltage, so you have to work quick if you are doing multiple bends in one piece, such as I was doing in this project. Fortunately this Rogue bender is easy to work with so quick setup changes are easy.

    This was done with 1-1/2" Sch40 aluminum pipe (1.90" OD, 0.145" wall), but I've also done this with the same results on 6063 T56 1-3/4" 16ga tube. I only had one bend rupture in that material, and that had less soap in the water than the others.

    This is bent on a 6" CLR die.
    Last edited by Chad86tsi; 03-30-2018 at 02:21 PM.
    Everlast 350 EXT - Thermal Dynamics Cutmaster 52 - Rogue Fabrication M600 xHD tube bender
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  2. #2
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    Re: Mandrel bendign tube and pipe on the cheap.

    Quite informative. If I ever get into alum tube I'll definitely have this stashed in whats left of my ol' brain.

  3. #3
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    Re: Mandrel bendign tube and pipe on the cheap.

    In theory it will work on any bendable metal. I'm going to try it on some stainless in a while, when I complete this project. Both tube and pipe. This bender has plenty of balls, it will bend 2" solids so frozen tube and pipe won't be a problem.
    Last edited by Chad86tsi; 03-30-2018 at 02:18 PM.
    Everlast 350 EXT - Thermal Dynamics Cutmaster 52 - Rogue Fabrication M600 xHD tube bender
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  4. #4
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    Re: Mandrel bendign tube and pipe on the cheap.

    Water needs to be soapy to work?
    American Welding Society - Certified Welding Inspector

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    Re: Mandrel bendign tube and pipe on the cheap.

    When I tried less soap, it just ruptured the pipe. clean water ice is pretty hard, the soap seems to allow it to break/crush, but still holds enough shape that it doesn't move out of the bend area.

    I froze some .049" wall (18 gauge) stainless tube last night, I'll try bending it this afternoon when the ice is good and solid to see what happens. If that will bend cleanly, I think anything will. It's 1-1/4" OD and will be bent over a 4.5" CLR die.
    Everlast 350 EXT - Thermal Dynamics Cutmaster 52 - Rogue Fabrication M600 xHD tube bender
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    Re: Mandrel bendign tube and pipe on the cheap.

    I gotta say it. Very cool!!!

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    Re: Mandrel bendign tube and pipe on the cheap.

    If soap is still made with some sort of fat, or fat like substance, I wonder if those molecules repel water, and form pockets in the ice. Enough to prevent the ice from becoming a true solid mass..........which allows it to give a bit. Probably wrong, but that's never deterred me before
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    Re: Mandrel bendign tube and pipe on the cheap.

    Seems like I have seen musical instruments built using soapy water to bend the pipes for trombones etc. They also said the water had to have just the right amount of soap for it to work right. This was bending brass tubing into 180 degree bends around a form as I remember. Seems you have found a way to get the results you wanted on the pipe bending. Are you just putting them into a freezer overnight to get them frozen.

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    Re: Mandrel bendign tube and pipe on the cheap.

    Quote Originally Posted by mwshaw View Post
    Seems like I have seen musical instruments built using soapy water to bend the pipes for trombones etc. They also said the water had to have just the right amount of soap for it to work right. This was bending brass tubing into 180 degree bends around a form as I remember. Seems you have found a way to get the results you wanted on the pipe bending. Are you just putting them into a freezer overnight to get them frozen.
    Yes, that is where I got the idea from. It was used on brass drawn tube, and formed over wooden forms. hundreds of years old technique. The formula that I have used that has worked is unscientific, but my best guess is one table spoon soap per quart of water. I've used just plain dawn dish soap. I give it a full 24 hours of freeze, if there is even a little soft ice in the middle, it seems to shift too much and collapse is more noticeable.

    I tried the 18 gauge stainless tube. It wasn't a full failure but would never count as acceptable. It didn't rupture or collapse anywhere. the inside wrinkled some, and the outside did flatten too much. Not unlike some of the bends you see in cheap production exhaust bends. It would never have bent even a few degrees without the ice mandrel, so it does indicate it would probably work fine on steel, and likely on thicker stainless. I'll try some schedule 10 316L pipe next.
    Last edited by Chad86tsi; 04-01-2018 at 11:25 PM.
    Everlast 350 EXT - Thermal Dynamics Cutmaster 52 - Rogue Fabrication M600 xHD tube bender
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