# How to bend 4 mm miniature aluminium pipe correctly into a circle?



## Simon Edwards (Jul 18, 2018)

Hello All.

I am looking for some helpful tips or guides on how to bend a miniature aluminium pipe in a circle that is 15mm across with a stem so it looks like a halo.

Its purpose is to be a cooling ring for a brass tip I intend to drill 1mm holes in the ring once its bend and use an air pump to push air through the pipe to the drilled holes.

I have tried bending it by hand but have been unsuccessful getting kinks and not a good circle.

I know I could use a brake pipe bender, but that will only get me 90 degs if I am right in thinking or not?

Any help is really appreciated.


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## misterfxt (Jul 18, 2018)

fill it tightly with sand and cap the ends. then try bending around a form. when done, pull the caps and blow or rinse the sand out.


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## Brian Rupnow (Jul 18, 2018)

Buy some of this material which is solid at room temperature but melts at 170 degrees F. Heat it to liquid, pour into pipe, wait for it to cool and solidify. Bend your pipe, then set pipe into boiling water to melt material and pour it out. The sand trick has never worked for me.
https://www.shop.boltonmetalproducts.com/Cerrobend-Bolton-158-5000-7-LB100004.htm


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## misterfxt (Jul 18, 2018)

Brian, if I new you were going to respond with another one of your great ideas if would have quietly sat back and read yours. Is that the same stuff used for casting gun chambers ?


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## Brian Rupnow (Jul 18, 2018)

I really don't know if its used for gun chambers or not. If you google it, you will see that one of the uses listed for it is bending pipes or tubes up to 1 3/4" diameter. and yes---really--I have tried the "fill it with sand and it won't kink" trick, and it never worked worth a darn. Neither has the "fill it with water and then freeze it" trick, which is the recommended way for bending thin-wall brass tubes to make trumpets.


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## Cogsy (Jul 18, 2018)

I agree with Brian and have used Cerrobend successfully. I will add that according to directions I found, coat the inside of the pipe with light oil (I used vegetable oil) and once the tube is filled with the melt, plunge it into cold/iced water for a rapid freeze. I didn't try it without following the directions so I can't say it wouldn't work dry, but it worked great using this method.


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## Henry (Jul 18, 2018)

You will need a longer piece that the one you will need bend in that shape, if not the ends will be very difficult to get close to the circumference. Fill it with something sand, sugar, salt...  and close the ends.   Try to do like an spiral around a mandrill with the appropriate diameter, a little bit smaller will be better because you will get some spring action. I am not sure in which direction you want to do the stem, but  I think that will be the easiest part.


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## Jasonb (Jul 19, 2018)

Most small tube is also quite hard, anneal it first, fill then bend.


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## TonyM (Jul 19, 2018)

Depending upon what exactly you are cooling with the airstream you may want to make the ring from larger bore tube. I spent a lot of time making air rings for cooling extrusions. If a good back pressure is not maintained within the ring the flow from each hole will vary considerably, getting weaker the further away from the supply air. That will result in uneven cooling.


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## minh-thanh (Jul 19, 2018)

Brian Rupnow said:


> Buy some of this material which is solid at room temperature but melts at 170 degrees F. Heat it to liquid, pour into pipe, wait for it to cool and solidify. Bend your pipe, then set pipe into boiling water to melt material and pour it out. The sand trick has never worked for me.
> https://www.shop.boltonmetalproducts.com/Cerrobend-Bolton-158-5000-7-LB100004.htm


Hi Brian Rupnow !
I have question : Is it reusable? Or use only once ?


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## Cogsy (Jul 19, 2018)

It's reusable Minh, I just re-used some yesterday. It's very handy when cutting and shaping thin tube/pipe as well as it stops it deforming while cutting or filing.


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## minh-thanh (Jul 19, 2018)

Thanks Cogsy !
Too much information to learn...


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## DJP (Jul 19, 2018)

I agree that the sand fill trick doesn't work. Don't waste time and material. The brake tubing bender would have been my suggestion making two half sections joined with 'T' fittings so that air can enter both sides. I'm not sure if this just has to be a practical solution or a pretty one too. 

I don't do pretty solutions well.


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## WOB (Jul 19, 2018)

misterfxt said:


> Brian, if I new you were going to respond with another one of your great ideas if would have quietly sat back and read yours. Is that the same stuff used for casting gun chambers ?



I'm not Brian, but I do know the answer to your question.   Cerrobend is formulated to expand slightly on cooling to grip the tube wall firmly so as to not slip during bending.

Cerrosafe is the metal used to cast gun chambers.   It is formulated to be exactly the same size at 30 min. after cooling after an initial shrinkage to allow withdrawal from the chamber.    This property allows accurate measurements to be made from the casting.    It does expand slightly over a long period of time( days).    So, for bending immediately after cooling, Cerrobend is the better choice.  Cerrosafe can be used, but it needs to age at least 24 hrs. after cooling for the best results.  Otherwise it will tend to break and slide inside the tube allowing a flat spot to develop.    It is less risky to use Cerrobend.

Lubricating the tube interior is actually detrimental to getting a good bend.  Cerrobend will not bond to the tube wall, so removing it is easy in boiling water.   You can always run a piece of stiff wire through the tube if you suspect there is residual metal in the tube.

WOB


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## stackerjack (Jul 19, 2018)

I have used Cerrobend, lots of times, with a good success rate. 
Another method I have used is to fill the pipe with lots of strands of fine wire. I personally use piano wire, because I've got lots of it, but other types of wire would be OK. If you use electrical wire, remove the insulation first. As always, practice on a scrap bit first. Make sure the pipe is FULL.
Jack


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## canadianhorsepower (Jul 19, 2018)

http://www.canadametal.com/wp-content/uploads/2016/08/bending-using-legend-products.pdf

this should be useful for all of us


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## Simon Edwards (Jul 20, 2018)

Hi All

Using the Cerrobend appears to be what I will do, got it on order as I type, it is for an air cooler for a hotend.

http://www.themakerhive.com/shop/ccdata/images/full3_6_45.jpg

Hopefully, the link works.  Reason for doing it here is that these are made in the USA and shipping is like $30 for something that costs like $13.  

You mention 


Jasonb said:


> anneal


  How would I do this.  I am totally new to this sort of thing.

Thanks all.


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## Brian Rupnow (Jul 20, 2018)

Anneal--Use acetylene with no oxygen. This gives a really oily black flame. Play it over the pipe until the entire pipe is black. Turn on some oxygen for a normal oxy-acetylene flame and play it carefully over the pipe until all of the black is burned away. At that point the pipe should be annealed. Careful not to get it too hot or--one minute the pipe is there, next second it's gone.


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## Cogsy (Jul 20, 2018)

By the looks of that link it doesn't need to be aluminium? If not, I'd change to copper instead. Copper anneals to a very soft state and is much easier to anneal than ali (IMHO). Simply heat it to a dullish red and plunge into water. If it hardens while you're working with it, just anneal it again. The Cerrobend will still work as well. I'd leave the pipe full of cerro while you drill the holes as well, there's less risk of breaking your small bits from grabbing as it breaks through a thin wall pipe.


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## Simon Edwards (Jul 20, 2018)

No I suppose it can be anything like copper brass or alu.


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## Wizard69 (Jul 21, 2018)

The fill the tube with sand method can work.  At least it works on hydraulic tubing that is also heated with a torch.   The question of annealing has come up, if the material works hardens you may find yourself having to anneal more than once.   

Im sitting here trying to understand this cooling ring.   Im assuming the jets would point to the center and that this would require a predrilled tube.  If so it might be a problem to keep what ever you fill the tube with in the tube.  

By the way whenever possible make a proper form to bend the tubing around.   Even better consider making a a bending machine that keeps the stress constant on the material as it wraps the die.    A proper tool will keep an even draw on the tube reducing the possibility of cracks.  

Some if the handheld tube benders out there will allow you to get close to 360 degrees if you release and get a second grip on the tube.  Close might be 300 degrees but it is better than nothing.  

Somebody mentioned air flow above and the starvation of ports farthest from the source.  This can be a real problem so the tube size and the port sizes must be chosen carefully.  This makes me wonder how much space you have because an alternative here is commercial spray nozzles which come in different widths and patterns.  

Another option would be a single port with a baffle that forces the air stream to circle around the tip.   Sort of like a squirrel cage fan in reverse.


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## Simon Edwards (Jul 21, 2018)

The holes are drilled after the bend is done, as the link shows the holes blow onto a nozzle that deposits filament, its a hotend from a 3d printer, the pipe is connected to a mini air pump that lows enough air around the nozzle to cool the filament, as the blower can be adjusted its air force is enough that it does its job. This is really a one-off job, not something that I will need 100s of, so making a machined form bender is beyond cost-effective.

http://www.themakerhive.com/shop/ccdata/images/full3_6_45.jpg


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## cds4byu (Jul 21, 2018)

Maybe 3D print a ring and then drill the holes?


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## Wizard69 (Jul 21, 2018)

If it is one off and that small id turn one on a lathe.   It would be a square ring upon which you would solder (glue or whatever) a closing ring.   You could have it done before you even get half way with the tubing.   



Simon Edwards said:


> The holes are drilled after the bend is done, as the link shows the holes blow onto a nozzle that deposits filament, its a hotend from a 3d printer, the pipe is connected to a mini air pump that lows enough air around the nozzle to cool the filament, as the blower can be adjusted its air force is enough that it does its job. This is really a one-off job, not something that I will need 100s of, so making a machined form bender is beyond cost-effective.
> 
> http://www.themakerhive.com/shop/ccdata/images/full3_6_45.jpg


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## Cogsy (Jul 22, 2018)

Why not just 3D print it instead? The cooling nozzle that came with my printer wasn't the best but one of my first prints was an improved design that worked far better. As long as you've got something to start with (so you can start printing), you can get the printer to upgrade itself. For a printer, the less weight on the print head the better so plastic would be my preferred material.


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