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Thread: Mandrel bender - GIF

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    Mandrel bender - GIF


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    Supporting Member hemmjo's Avatar
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    Very nice, what was inside the tube to keep it from crushing?

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    old kodger's Tools
    Quote Originally Posted by hemmjo View Post
    Very nice, what was inside the tube to keep it from crushing?
    My question also. I have used very dry sand in the past but on a short piece of pipe like that it takes a lot of "plugging" to stop it from just issuing out the end.
    I suppose it could be plaster of paris.

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    That is the mandrel. Some are bars with a shaped end that finishes at the bend point, some are balls linked together and in this case disks linked together.
    The object is to support the tube from the inside at the bend point to prevent deformation. This guy is doing a first class job, those bends are super smooth.

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    old kodger's Tools
    Quote Originally Posted by NortonDommi View Post
    That is the mandrel. Some are bars with a shaped end that finishes at the bend point, some are balls linked together and in this case disks linked together.
    The object is to support the tube from the inside at the bend point to prevent deformation. This guy is doing a first class job, those bends are super smooth.
    There is some sort of "goop" in there as well, you can see that it has dripped out onto the machine at 0.20.

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    Supporting Member Saltfever's Avatar
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    Look at 0:43. Those cups in the vise are lubricated to help promote slipping. As Norton pointed out, sometimes, balls are used. "Mandrel" is the operative word that tells you something rigid is inserted inside to prevent collapsing. I have used sand, melted solder, melted lead, etc. After the bending the tube is heated and the low temp metal flows out. Cleaning is always a problem. I have even filled with water and then froze copper tube with mixed results. Both ends have to be crimped shut and then cut off later. I don't think those methods are considered "mandrel" bending.
    Last edited by Saltfever; Sep 5, 2021 at 11:25 PM.

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    Supporting Member mwmkravchenko's Avatar
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    Quote Originally Posted by Saltfever View Post
    Look at 0:43. Those cups in the vise are lubricated to help promote slipping. As Norton pointed out, sometimes, balls are used. "Mandrel" is the operative word that tells you something rigid is inserted inside to prevent collapsing. I have used sand, melted solder, melted lead, etc. After the bending the tube is heated and the low temp metal flows out. Cleaning is always a problem. I have even filled with water and then froze copper tube with mixed results. Both ends have to be crimped shut and then cut off later. I don't think those methods are considered "mandrel" bending.
    Roofing tar also works. That is used in some lighter gauge tube bending. The tar is poured in and then left to solidify.

    In the video it almost looks like plastercine and metal pucks.

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    It is 'drawing lube', very much like what reloaders use cold forming cartridge cases. Another technique makes this work; the weld is "on edge" of bend, not inside or outside, likely to fracture.
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    Toolmaker51
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    Quote Originally Posted by NortonDommi View Post
    That is the mandrel. Some are bars with a shaped end that finishes at the bend point, some are balls linked together and in this case disks linked together.
    The object is to support the tube from the inside at the bend point to prevent deformation. This guy is doing a first class job, those bends are super smooth.
    I have always wondered how those little mandrel discs are coupled together to allow articulations while bending is performed.

    Anyone have a few pictures of the ball mandrels used in tube bending with supporting the tube or pipe during the bending process???

    cheers

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    Disc-like mandrels are more like truncated spheres. The flats allow them closer spacing and therefore smaller bend radii.
    Also, thinner wall tubing runs better with those close intervals.
    Sincerely,
    Toolmaker51
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