Mandrel bender - GIF

Mandrel bender.

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Previously:

https://www.homemadetools.net/forum/...896#post183620
https://www.homemadetools.net/forum/...505#post177822
https://www.homemadetools.net/forum/...933#post171599
https://www.homemadetools.net/forum/...204#post165405
https://www.homemadetools.net/forum/...125#post157533
https://www.homemadetools.net/forum/...198#post149888

Very nice, what was inside the tube to keep it from crushing?

Quote:

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Originally Posted by hemmjo

Very nice, what was inside the tube to keep it from crushing?

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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.

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.

Quote:

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Originally Posted by NortonDommi

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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There is some sort of "goop" in there as well, you can see that it has dripped out onto the machine at 0.20.

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.

Quote:

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Originally Posted by Saltfever

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.

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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.

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.

Quote:

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Originally Posted by NortonDommi

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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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

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.

hi Toolmaker51 Toolmaker51, The reason i ask is i would like to machine a few mandrel balls "truncated sphere" for one of my tube benders and some tighter radius tooling also.

Glad you ask, point of this site afterall.
With a radius cutting arrangement, I'd drill the link hole before removing from chuck. A full sphere wouldn't be required, part off through the neck. That would aid fixturing to mill flats.

If you were to lay out profile desired, in CAD or mechanical drafting, simple templates might reveal the particulars of mandrel.

The multiple disc mandrel on a steel cable is pulled around as the tube is bent. You can see the slight ribbed sections caused by each disc between .34 to .36 and at .37 you can see these discs are pulled backwards through the bent tube making it perfectly round again.