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Stepside
09-17-2007, 11:42 AM
If I remember correctly Evan mentioned using salt to fill tubes when bending. If so what kind of salt and any other tecniques that are important. I am wanting to bend some thinwall brass tubing and keep the cross section as pure as possible.

BTW it is Evan's fault that I have this problem. I read about all the joys of "retirement" and watched him complete about a million large tasks in the shortest of time. So after 42 years in the classroom as a Machine shop/Drafting/CAD/CAM instructor I too retired. Where is all the "free time" to get my stuff done. The "honey Do" list looks like an encylopedia and the "lets do something" list is just as long. I envisioned quiet time in my shop building a set of street clock works followed by a beam type steam engine ect.

Actually a great big "Thank You Evan" as I now have time to do the "Honey Do's" as they should be done rather than "quick and dirty's" because of the length of a weekend and the demands of employment.

Forrest Addy
09-17-2007, 11:48 AM
Anything granular that can be packed tight will work for a bending medium. Makers of musical instruments use rosin for bending brass tube for trumpets etc. Melt out the rosin and they have a nice bend. Then they jig the bend and force steel balls through it to round it back up.

A.K. Boomer
09-17-2007, 12:24 PM
No expert here but do realize that this is most probably an "art" and could get extremely involved with size/compression/and shape of the material at use, for instance i would imagine salt and sand as two different things as the salt would more redidly give way to turning into a powder, could also imagine using H20 and sealing ends off before bending would give results anywhere from a broken tube to just what you wanted depending on what your trying to bend in the first place... round steel bee-bee's, lead shot, you get the idea, Now for Evan to post his already bookmarked website on the subject:p

A.K. Boomer
09-17-2007, 12:39 PM
Then they jig the bend and force steel balls through it to round it back up.


I just caught that,, one example; enter formula V race engines where they are held down to stock parts in just about every catagory, along with stock compression and everything else, but you can heavily modify many of the stock parts, like the intake manifold, they extrude hone them (force an abrasive/clay compound through them) they acid etch them, they do about anything they can to open up the I.D. and make them flow as good as possible --------- some guys spend an ungodly amount of time on them, get them to flow better on a flow bench better than any of their other previously modified manifolds including running steel balls through them for the final touch to remove any little dents or tight spots ----------- Bolt them on the race car and go to test on the track - hit turn #1 and have to lift (de-accel) only to suck a hole in the manifold because the metal was so thin:rolleyes:

Evan
09-17-2007, 01:10 PM
Salt for bending is a very old trick. It works well because of the cubic shape of the crystals which prevents them from sliding around under compression. Other granular materials will work but many are rounded (sand) and won't hold shape as well. The other major benefit is that salt can be washed out with water ensuring that absolutely not one grain of grit remains.

TGTool
09-17-2007, 01:46 PM
We used to use salt for making copper tube induction coils at a place I once worked. The tube was flattened somewhat through the middle section leaving the ends untouched for connectors. Then the tube was filled with salt and formed into the required flat coil (tube on edge). When the coil was done they were thrown in a tank of hot water for a time with occasional agitation to get the salt dissolved and out. It always worked.

kap pullen
09-17-2007, 01:48 PM
I've seen ice used to fill a tubular handrail for bending.

Sheetmetal, and precision assembly guys at NASA did this.

Just let it sit at room temp for a while and be done.


Also seen of teflon bar inserted, and pulled out when done.

This was done on plastic pipe with a bit of heat.

Kap

Alistair Hosie
09-17-2007, 01:52 PM
PLUMBERS HERE USE A WELL FITTING SPRING FOR bending tube copeer etc.This can be pulled out with a piece of string Alistair

stuntrunt
09-17-2007, 02:11 PM
For bending odd shapes like spouts for silver tea- and coffeepots, you can fill them with lead. After bending, just melt out the lead. Be careful though... ANY lead left will burn holes right through your creation when hardsoldering it onto something.
The residual lead willl alloy with the other metal and very locally lower the meltingpoint.
To prevent this you usually coat the inside of the tube, spout, ... with yellow ochre before pouring in the lead.
This trick is very well described by Rupert finegold and William Seitz in 'Silversmithing'. Really, really, really great book!

dp
09-17-2007, 02:23 PM
Salt crystals are shaped like cubes. The theory of using cubes in bending can be visualized by stuffing a bunch of shoe boxes in a large water pipe and pushing them all to the other end. They slide along like box cars, all neatly aligned. Any other shape will cause interlocking and binding and finally a jam because they will push outward as well as in line with the pipe.

DR
09-17-2007, 02:31 PM
Step',

Some tube benders have formulas using the wall thickness and OD of tube as important parameters to determine the difficulty in getting a nice bend.

One such formula says that if the ratio of the wall to OD is .07 or less internal support of some kind is needed. For instance: 1/16" wall, 2" OD would be .062/2=.031. That would need some internal support. Of course, these formulas assume a good set of bending dies.

What are your numbers for wall and OD? And what kind do bending dies do you have?

I'm no fan of packing sand or salt into a tube and sealing the ends, a hassle. Cerrobend (low melting point alloy) is good. Freezing the tube with water is good too, don't freeze super hard though. Whatever method, pushing ball through is a final step.

IMO, the bending dies are the most important factor. Without good dies you're asking for problems. Some people try to bend with the cheapo import pipe benders which don't do much of a job.

BTW, some one is sure to ding me on the 2" OD example I used. Exhaust pipe of that size is bent all the time without internal support. But, exhaust bends aren't usually very good unless an internal mandrel is used. Plus some exhaust dies are purposely made to wrinkle the inside radius so the aluminized coating isn't thinned.

A.K. Boomer
09-17-2007, 02:39 PM
Salt crystals are shaped like cubes. The theory of using cubes in bending can be visualized by stuffing a bunch of shoe boxes in a large water pipe and pushing them all to the other end. They slide along like box cars, all neatly aligned. Any other shape will cause interlocking and binding and finally a jam because they will push outward as well as in line with the pipe.


brilliant analogy DP, and very true to some degree but im wondering what happens along the inner and outer turns with this as the inboard turn gets shorter and the outer gets longer, do the "boxcars" simply "swap rails" whilst under pressure? now that you mention it --- I wonder about all kinds of shapes including triangles, but the almighty sphere might be tough to beat in certain aplications as it is influenced in all directions is it not?
This is a very interesting topic as with the different shapes sizes and compounds along with the different material tubes and thickness and even shapes (square tubing) the posibilities are endless...

lazlo
09-17-2007, 03:04 PM
I'm no fan of packing sand or salt into a tube and sealing the ends, a hassle. Cerrobend (low melting point alloy) is good. Freezing the tube with water is good too, don't freeze super hard though. Whatever method, pushing ball through is a final step.

How do you force the ball around a corner? Do you press one ball as far along as possible with something like a Porta-Power, and then follow with enough balls to make the curve?

Stepside
09-17-2007, 03:47 PM
So the distaff side of the household asked me"What kind of salt?" I replied "the salty tasting kind". So I got the long long lecture on Kosher Salt and Sea Salt and Iodized Salt followed with the "Why" question, hence the question that started this post.

As to benders I have a good bender that is capable of 1-1/4 pipe and I have the dies for the desired 1 inch tubing.

Evan
09-17-2007, 09:04 PM
Salt crystals are shaped like cubes. The theory of using cubes in bending can be visualized by stuffing a bunch of shoe boxes in a large water pipe and pushing them all to the other end. They slide along like box cars, all neatly aligned. Any other shape will cause interlocking and binding and finally a jam because they will push outward as well as in line with the pipe.

While it sounds right that isn't what happens. Salt crystals are indeed cubes. Cubes however are not self organizing like spheres are. What happens is the salt crystals end up randomly arranged and resist movement in any direction including the easy ones.

This can be shown by taking a tube and fastening a light weight piece of material such as a tissue on one end with a rubber band. It should be just secure enough to hold the tube full of salt for six inches or so. Then fill the tube with that much salt. Take a stick or similar object and try to push the tissue off the end of the tube by applying pressure to the top of the salt column. It's impossible as the random alignment of the salt crystals ends up transferring all of the force to the sides of the tube causing the crystals to lock in place.

dp
09-17-2007, 09:37 PM
While it sounds right that isn't what happens. Salt crystals are indeed cubes. Cubes however are not self organizing like spheres are. What happens is the salt crystals end up randomly arranged and resist movement in any direction including the easy ones.

This can be shown by taking a tube and fastening a light weight piece of material such as a tissue on one end with a rubber band. It should be just secure enough to hold the tube full of salt for six inches or so. Then fill the tube with that much salt. Take a stick or similar object and try to push the tissue off the end of the tube by applying pressure to the top of the salt column. It's impossible as the random alignment of the salt crystals ends up transferring all of the force to the sides of the tube causing the crystals to lock in place.

That would certainly explain the evil grin on the face of the guy who told me the boxcar story :)

aostling
09-17-2007, 09:43 PM
While it sounds right that isn't what happens.

Evan,

This is a wonderful explanation of the phenomenon. As a thought experiment your example is perfect, and I have no doubt it would work as you say.

A.K. Boomer
09-18-2007, 12:03 AM
How do you force the ball around a corner? Do you press one ball as far along as possible with something like a Porta-Power, and then follow with enough balls to make the curve?


Yup, or in some cases a drift and a hammer...

dewat
09-18-2007, 02:24 AM
How do you force the ball around a corner? Do you press one ball as far along as possible with something like a Porta-Power, and then follow with enough balls to make the curve?

On "How its made" there was a piece on trombones, they used the frozen water method, then they clamped the "u" shaped piece in a fixture and pushed balls through it with basically an arbor press, the first ball is the final I.D. all of the following ball are under size.

GeorgePapa
09-18-2007, 09:29 AM
Hi stepside,
have been faced with same problem and solved it (to my satisfaction) by first flame softening the work hardened tube and filling it with lead after fluxing it.
There was some deformation though...

George

hornluv
09-18-2007, 01:45 PM
Hi Stepside,

Finally I have a post that I feel fully qualified to answer. I make custom French Horns so I'm always bending thin walled (.015" to .020") Yellow Brass, Nickel Silver, and Gold Brass. For most gentle bends I use pitch, which is an asphalt tar substance. Bending pitch is different from chaser's pitch, though. I've only found it from one of my suppliers and they only sell to established businesses. If you need a small amount I can send you some or you can buy a gallon of it through me. I'm more than happy to help.
The pitch is formulated to bend properly at around 70* F. If it gets too warm the tube starts to get egg-shaped, much like if you use sand. If it is too cold, it is more brittle and you tend to get wrinkles on the inside of the bend and stretch marks on the outside. It will warm up pretty quickly in your hands and I cool it back down by putting the tube in water for a few minutes.
For more severe bends, I use Cerrobend, which is a low melting point alloy. You can get it from McMaster-Carr but they want a lot for it. I got mine on eBay for about $7 a pound. You won't be able to bend this by hand. First, soak the tube in oil, I use 30 weight, and let it drain. This keeps the cerrobend from soldering to the sides. The cerro melts at 158* so you can melt in hot water. I use a ladle to get it in the tube with the end plugged up by a vinyl cap and sitting in water. The cerro isn't so hot that it will cause a steam explosion. Once the tube is filled, put it in cold water, otherwise the cerro crystals grow quite large and it is very brittle along the crystalline boundaries. It will break and come through the sides of the pipe. When you're ready to bend, soak it in hot water straight from the tap for about 10 minutes. This makes it far less likely to break. As you bend, look for wrinkles and hammer them down as soon as they appear. Otherwise you're going to be tapping down a mountain. Melt it out again in boiling water. Make sure you get it all out because it will burn into the tube if you anneal the tube and there's still cerro in it.
For balling out, get a ball the size of the ID of the tube and a ring with rounded inner edges that is the size of the OD. Oil it up and ram it through the tube. I use a drift to get it up to the first bend, then I use other balls to make it around the bends. If you're going to do a lot of parts, you might want to consider a ball out mold, which is just a mold of the outside shape of the part that holds it in place and keeps it round. In lieu of a mold though, just hold it and occasionally run it through the ring mentioned above to round it out. You might have to anneal several times and you'll be tapping down wrinkles as well. Sand out the hammer marks when you're done. Hope this helps.

Stuart

DR
09-18-2007, 04:37 PM
.............
I'm always bending thin walled (.015" to .020") Yellow Brass, Nickel Silver, and Gold Brass.
....................
As you bend, look for wrinkles and hammer them down as soon as they appear. Otherwise you're going to be tapping down a mountain. ............

Horn',

What do you use to bend with? Tube bender, something else?

You mention wrinkles, that implies to me you don't have a fancy tube bending setup, huh?

hornluv
09-19-2007, 11:58 AM
For gentle bend, greater than a 2 inch radius, I bend by hand to fit the spot that the bend needs to go. For tighter bends, I have a jig that consists of a 12"x12", .750" thick steel plate with lots of holes in it. There's a spot for bolting down a bending die, which I make as needed and then a vice that holds the tube against the die. I then have a long handle which is curved at the end and has a pin that fits into the holes in the plate. I put the handle into one of the holes and bend until I lose leverage and then move to the next hole. Wrinkles tend to form along the inside of the bend because of the compression that's happening. If you bend the tube around in such a way that you are pulling the tube as well, you increase the stretching on the outside and decrease the compression on the inside, thereby decreasing the wrinkling too. Easy to do by hand, not so much with a jig.

ProGunOne
10-13-2007, 02:36 AM
On "How its made" there was a piece on trombones, they used the frozen water method, then they clamped the "u" shaped piece in a fixture and pushed balls through it with basically an arbor press, the first ball is the final I.D. all of the following ball are under size.

I just watched How It's Made and they showed a company that made trumpets. They formed the bell and main tube on the lathe (metal spinning?) Showed them forming the bell or large end, rolling over the end, soldering in a wire, etc. To acheive the bend in the main part of the horn they used soapy water that they froze to -56 and bent it around a jig. Interesting.

Vintage Mutes
01-11-2008, 05:13 PM
On "How its made" there was a piece on trombones, they used the frozen water method, then they clamped the "u" shaped piece in a fixture and pushed balls through it with basically an arbor press, the first ball is the final I.D. all of the following ball are under size.

Actually most horn makers use a water/detergent mixture which freezes without the expansion that occurs with pure water. The mixture forms more of a slush. Working time is limited, but cleanup is much easier than the old way.

They used to pour molten pitch into the tubing, let it cool, then bend, then melt it out. Problem with pitch (besides the dangers of handling what is basically red hot tar) is that you have to use kerosene or mineral spirits to get it all cleaned out.

For non-production bending, most horn makers I know of use Cerro-Bend or other Bismuth based alloys. These melt in a saucepan on a stove, usually at about 175 degrees F I think. And can be melted out after you bend.