View Full Version : Thought on bending metal tubing...

02-07-2011, 10:40 PM
Had a thought one could fill a metal tube with a low temp alloy like Cerro-safe to prevent getting a kink while hand bending. Anybody ever done this? Thoughts?

02-07-2011, 10:48 PM
I have not used a low temp alloy, but I have used SALT. Plug one end, pour the tube full and plug the other end. You can then just brute force the tube around a pipe or similar round pattern. Of course, tube benders are easier.

02-07-2011, 10:49 PM
Use sand. :)

02-07-2011, 10:52 PM
Yeah, my Dad did some nice bending of aluminum tube by filling it with sand.


02-07-2011, 11:23 PM
The problem with sand/salt is its granular and you're faced with having to contain the stuff. A low temp alloy would form a solid rod that could easily be melted out afterward.

02-07-2011, 11:32 PM
im pertty sure there are alloys designed for filling pipes for bending.. or at least, advertised for such.

J Tiers
02-07-2011, 11:32 PM
And salt/sand can pack tighter and allow flattening. The alloy is harder to flatten

02-07-2011, 11:44 PM

02-07-2011, 11:58 PM
I have not used it myself but have seen it done successfully several times.
Apparently this is one of the primary uses of the alloy.


A quote from the applications page....

"Tube Bending: Bending of thin-walled tubing and channels without adequate support can wrinkle, flatten, or rupture the part wall. Bolton Alloy 158 and Bolton Alloy 255 have long been used to support work pieces during bending or formatting to prevent damage. Normally the part should be lubricated before filling to prevent galling and to allow for clean alloy removal. The growth property of the alloys ensures complete part filling, and flaws in a tube wall can often be detected by bulges or leaks of molten alloy through microscopic cracks.
Bolton Alloy 158 is the most widely used for this application, and it can be melted out with hot water. Bolton Alloy 255 is used for tubes with diameters larger than 1.5 in.; however, a hot oil bath or oven heating is required to reach the 255F melting temperature.
With Bolton Alloy 255 the tube or channel can be bent as soon as the alloy solidifies. Bolton Alloy 158 must be rapidly cooled by immersion in cold, circulating water or other quick chilling medium immediately after filling. This results in a fine grain crystalline structure that adequately supports the work piece during formation."

02-08-2011, 12:12 AM
Use sand. :)

Yup, if you are using heat you have to use dried sand.

02-08-2011, 04:44 AM
Just be careful what sort of sand. I once filled a tube with sand, sealed it, bent it - worked pretty well. I then tried to get the sand out and discovered I'd used paving sand. It comes with binders in it that allow the sand to lock into the bricks, particularly if it gets wet. It also locks together when heated.


02-08-2011, 05:09 AM
How about this one: I saw a fellow making a trombone on television and he filled brass tubing with soapy water and froze it; the narrator said the soap prevented the ice from shattering during the bend.

02-08-2011, 08:10 AM
Some great posts and info on this subject, thanks all!

02-08-2011, 09:52 AM
I'll qualify my previous post by saying that maybe if you're bending a one foot by3/8" tube then the low melt stuff might be great...and probably not expensive.
The reference to what my Dad would do was more along the lines of 3/4" x 4' formed around a 55 gallon drum....that might be costly using the low-melt stuff :)


02-08-2011, 10:15 AM
ZINOM, agreed, My interest would be more on the order of making fuel lines and such, definitely smaller stuff.

02-08-2011, 10:21 AM
I use Cerrobend to bend some of my tubes. It can be a bit persnickety. First of all (especially if the tube is brass), coat the tube with oil to prevent it from getting tinned. Secondly, don't let it air cool. The crystals can get really large when air cooled and are brittle at the crystalline boundaries so it tends to break and come through the wall of the tube. Pour the Cerrobend into the tube and dunk it into cold water to cool it fast and keep the crystals small. You're below the boiling point of water when it melts, so you don't have to worry about a steam explosion. Lastly, before bending, I soak the part in hot water straight from the tap to make it more malleable (I soak for about 10 minutes for a 1/2" tube). I don't get any breakage doing it this way. Then just melt it back out using hot water and clean the tube with degreaser and scrub brushes to get the remaining bits of Cerrobend out.

02-08-2011, 12:58 PM
30 years ago I had a job rolling copper tubing into 5" diameter coils. I soldered a cap on one end of the 60 foot roll of tubing. I rolled the tubing out straight. Someone got on the roof of the building with the open end of the tubing. The tubing ran down at an angle across the parking lot. We had the fork lift hold the tubing up at one spot. We had a person on a step ladder hold it up at another spot. We had another person holding it up standing on the ground. The person on the roof poured in the DRY sand and we all tapped on the side of the tubing to make it compact tighter. After about 10 minutes of tapping it would not compact any tighter so we soldered a cap on the other end of the tubing. We used the lathe and a roller on the tool rest to wind the tubing around a pipe chucked in the lathe. Put the tool rest in gear correct threads per inch to keep up with the tubing as it winds up. Roller needs a radius to match the tubing diameter. Then we cut the caps off both ends and drained out the sand. You can tie a knot in a piece of tubing and it will not kink if it is full of sand.

You can buy a 50 lb bag of Play Sand at Lowe's $3 a bag is it already dry.

02-08-2011, 01:58 PM
I agree with Cami....I'd fill the tube with soapy water, freeze it, and bend it that way. Many times bending thin-wall tubing, heating it can change the temper (hardness) of the metal, and then you got problems.
I saw the same show where they were bending the brass for that trombone...pretty cool.

When I worked in a muffler shop we used a hydraulic bender to cold bend steel tubing. Some guys prefer mandrel bent tubing, but, take it from somebody who has been there, the tubing around the outer radius of the the bend is awfully thin. In a commercial business, mandrel bent tubing doesn't last as long as cold formed tubing bent with dies.

02-08-2011, 03:01 PM
I used Cerrosafe to bend some 5/16" aluminum tubing in about 1" radius bends. It is not the ideal alloy to use because it does not expand very much as it cools until several hours have passed. However, I had it on hand so decided to try it out. I tried bending some pieces as soon as the alloy had cooled, but it tended to snap at the apex of the bend and slip down the tube . This left a void where the tubing would buckle.

I discovered that if I let the filled tubing age overnight, it would bend properly. "Cerrobend" is formulated to exand quickly as it cools, gripping the inside of the tubing tightly. So if you are going to buy some, make sure it is Cerrobend.


Alistair Hosie
02-08-2011, 03:30 PM
I saw aprogramme on tv also showing making tubas, and horns ,trumpets ,etc they filled the tube with a form of pitch then when done heated it up and poured it out.I think you would need to enquire more about this as it could prove to be very messy , but I fancy wax would work too. I know in plumbing the used springs of a lightly smaller size and pulled them out whyen finished I tried this and it works great.Alistair

02-08-2011, 04:01 PM
My grandfather told me moonshiners would use river sand to bend the worm for there moonshine stills. They would close off one end of the copper tube then fill it with river sand. They would drive a wood plug in the other end to pack the sand and bend it around a tree stump.

02-08-2011, 07:05 PM
So that's where Tennessee whiskey comes from...

Cook up a batch of 'shine and darken it with shoe polish....instant "Jack Daniels"

02-08-2011, 07:53 PM
A true shiner takes great pride in the clarity of his shine. He would never darken it. I once took a tour of the Jack Daniels brewery. That was the biggest fanciest still I ever seen. They have the original brewery setup for tours and it has the original copper still. That is the most copper I have ever seen in one place.

02-08-2011, 08:02 PM
I've used playground sand baked to get out the moisture. Weld a cap on one end and then fill and then tap out the sand until it settles and repeat until it doesn't settle any more. Weld another cap on the end. I bent up some 1.125" x 0.120" wall handlebars this way.

If you are just doing fuel lines wouldn't one of those hand benders do it?


02-08-2011, 09:26 PM
If you are just doing fuel lines wouldn't one of those hand benders do it?
I was more or less using that as an example of scale. If I'm not mistaken the hand benders are somewhat limited in the range of radii that can be formed.

02-08-2011, 09:50 PM
I was always told that the stuff to use was sodium thiosulphate which is a super saturated crystal. When the crystals are heated a little they dissolve in their own water of crystallisation and they turn into a liquid which is poured into the pipe. Upon cooling the liquid becomes crystalline again and the pipe or tube is bent after which it is heated and the sodium thiosulphate runs out.

Sodium thiosulphate is also pretty harmless - it is used as an antidote for cyanide poisoning. I see it is $50 for 10 lbs of crystals shipped on Ebay - sold as a water dechlorinator. (also spelled thiosulfate)