News:


  • March 28, 2024, 01:56:56 PM

Login with username, password and session length

Author Topic: Bending Aluminum Tubing  (Read 2922 times)

Offline JHildreth

  • 23 supporter
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 162
Bending Aluminum Tubing
« on: February 02, 2019, 09:44:04 PM »
I am back working on my FW 190 project.  I have fabricated the exhaust manifolds from brass tubing, but I am not completely satisfied with them.   I decided to try again but use aluminum this time.  I have used bent brass tubing any number of times, but I have never bent aluminum tube to any degree before.  I searched this forum and discovered a previous post by Larry Renger that discussed the process for annealing aluminum tubing.  I did not find any discussion on the actual technique for bending the tubing after annealing.  I need to bend 5/16 in tubing 30-40 degrees with a radius of 3/8 to 1/2 inch.  I won't know the exact specs until I try a few to get what I want.  My efforts so far have all collapsed the tubing such that I can't use the results.  I know someone out there has done this before successfully.  Please help.

Thanks.

Joe

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Bending Aluminum Tubing
« Reply #1 on: February 02, 2019, 09:54:55 PM »
It's going to be a challenge for such tight bends.

DuBro makes some tubing benders that are basically spring-like things that go over the tube.  I suspect that those won't help for such tight bends.

If you're really committed, watch some YouTube videos of brass instruments (trumpets, tubas, etc.) being made.  They manage to make very tight bends in brass tubing by filling the tube with pitch, then bending, then melting the pitch out.  It'd be a lot of work (for starters, you need to find the right pitch!), but if anyone knows how to bend tubes by hand, it's high-end musical instrument makers.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Larry Renger

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3995
Re: Bending Aluminum Tubing
« Reply #2 on: February 02, 2019, 10:02:25 PM »
There are a couple of standard techniques. Easiest is to find a set of spring bending guides. These are springs that fit tightly over the tube and prevent collapse. I don’t have a source, but bet they are still available.

The second way is to plug both ends of the tube after filling it with sand. The filler also won’t allow collapse.

For small tubing I use weedwhacker line inside. You might achieve the same thing with Tygon tubing. Perhaps a couple of nesting tubes to provide internal reinforcement. The tubing is easily removed after bending (maybe greased first?)
Think S.M.A.L.L. y'all and, it's all good, CL, FF and RC!

DesignMan
 BTW, Dracula Sucks!  A closed mouth gathers no feet!

Offline Gary Dowler

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1017
Re: Bending Aluminum Tubing
« Reply #3 on: February 02, 2019, 10:16:03 PM »
An idea occurred to me, I have no idea if it will work.
Du-Bro makes a bender for 5/32 tubing. If that size will work then try this. Sort of Hydro forming.
Take your tube, pinch an end completely closed. Fill with water, pinch the other end closed. Bend it. (Might have to insert the tubing into the bender before filling and pinching.  Might work. 

Gary

Edit; just realized you need 5/16, not 5/32. You would have to source another type of bender.
Profanity is the crutch of the illiterate mind

Offline Larry Renger

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3995
Re: Bending Aluminum Tubing
« Reply #4 on: February 02, 2019, 10:46:42 PM »
You may have to anneal it more than once, after a partial bend, just to be safe.

Let us know what you try and what works! You are doing pioneering work here, pushing back the frontiers of modeldom.  H^^

PS: buy lots of tubing.  VD~
Think S.M.A.L.L. y'all and, it's all good, CL, FF and RC!

DesignMan
 BTW, Dracula Sucks!  A closed mouth gathers no feet!

Offline Robert Whitley

  • 21 supporter
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 287
Re: Bending Aluminum Tubing
« Reply #5 on: February 02, 2019, 10:56:31 PM »
I have had very good success by plugging one end of the tubing then filling with water and freezing it.
Be sure to only plug the bottom so that the ice can expand out the open end and thus not swell the tubing.
Do your bending by whatever means is available to you and let the ice melt.
Good luck and be sure to post whatever method works for you.

Offline Gary Dowler

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1017
Re: Bending Aluminum Tubing
« Reply #6 on: February 03, 2019, 12:27:29 AM »
I have had very good success by plugging one end of the tubing then filling with water and freezing it.
Be sure to only plug the bottom so that the ice can expand out the open end and thus not swell the tubing.
Do your bending by whatever means is available to you and let the ice melt.
Good luck and be sure to post whatever method works for you.
When I had my idea above I hadn't thought of freezing it. Interesting.

Gary
Profanity is the crutch of the illiterate mind

Offline RC Storick

  • Forum owner
  • Administrator
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12393
  • The finish starts with the first piece of wood cut
    • Stunt Hangar
Re: Bending Aluminum Tubing
« Reply #7 on: February 03, 2019, 01:42:29 AM »
I had this problem once. I gave NASA in FL a call and asked to speak to an engineer and asked him how they do it. He said they fill it with liquid nitrogen. I told him I had no access to this he said the next best thing was to fill the tube with Bismuth. Bismuth is a low melting point metal. It turns to liquid with hot water. Fill the tube with the metal and bend. After bending run it under the hot water faucet and pour the metal out. It worked perfectly.

 Bismuth metal is great for element collectors, crystal makers or any one who has a use for a low melting temperature metal. It is a non toxic metal with symbol Bi and atomic number 83 Element 83 has quite the repertoire of unique features: Low melting temperature making it perfect for DIY casting projects and alloying. With some practice, you can make beautiful hopper crystals. The most diamagnetic element (repels magnetic fields). Has one of the lowest thermal conductivity values among metals. Expands upon solidification like ice from water, and can be used to make a tight-fiting casting such as typesetting. Makes an excellent lead substitute due to being non toxic, although you should still wear protection when handling it. In earth's crust, it is twice as rare as palladium and only twice as abundant as platinum and gold.

https://www.amazon.com/Bismuth-Ingot-Chunk-99-99-About/dp/B07MJ3QSVS/ref=sr_1_11?s=industrial&ie=UTF8&qid=1549183531&sr=1-11&keywords=bismuth+metal
AMA 12366

Offline Dave Hull

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1901
Re: Bending Aluminum Tubing
« Reply #8 on: February 03, 2019, 02:43:51 AM »
Joe,

My most recent similar bend was on some hardware store ¼” aluminum tube used for the pilot light on a furnace. I’d have to go measure my sample, but I hand formed it around a grooved wooden disk to a centerline radius of about 3D.  (Going by a photo I took.) It was not particularly difficult, but going tighter would take a lot more effort. Using 3D applied to your 5/16 tube, you are looking at nearly an inch of bend radius, which is twice what you hope to achieve. So this is going to be challenging. I think I have a book that has aerospace minimum bends in it, but that will take some digging.

Using Cerrobend material is an industry method of doing what you are trying. As such, my thought is that it would be more suitable than pitch, sand, frozen water, or weed whacker string. It is a very low melting point alloy designed for just this purpose. The lowest melting point alloys contain cadmium, so know what you are doing before you pick that. The lowest Cad-free alloy melts at 203F, which isn’t up to the full annealing temp of aluminum. So you don’t have to risk working with heated cadmium for this method. Here's some info:

     https://www.industrialmetalsupply.com/Products/specialty-metals/cerro-bend#1

You can also look in McMaster-Carr. They try not to use brand names, but if you search using Cerrobend, it will take you to the same stuff.

You could also try solder, but the melting point moves up into the mid-400F range. I’m sure you have some of this around, so you could try that almost for free. Because of your very tight desired bend radius I would combining the solder plug with a grooved wooden form. You can make a straight grooved wooden block to use as a wiper die. If you get serious, make a steel strap that pivots around your radius block and holds the wiper die in tight. You are now getting close to….

The best way to bend tubing is with an actual mandrel style tubing bender. These have a series of hardened steel balls all linked together that fit into the tube. (Looks kind of like a keychain....)  The machine pulls on the tube, so you do not get failure on the inside of the bend from buckling. The smallest one of these I have personally used was either 3/8" or 1/2" diameter.  It has grooved guides somewhat similar to the DuBro tool, as well as clamps. Go to Utube and find some videos on mandrel style bending. It may give you some ideas.

If you are using K&S tubing, I'd be concerned that the .014 stuff is so thin that it will fail in a tight bend. I’d try either their .049 or .035 wall tube. I recently wanted to bend some 3/32"(?) K&S aluminum tube. I tried Larry's weed whacker trick but it did not work well for me. The tube buckled before I got the bend I needed. I will try some of these other methods when I go back to that part of the project. (It was for a cockpit control stick.)

Here’s a possible alternative, if you are going to paint them. Make a curved mandrel out of something suitable. (I’d try a piece of fuel tubing unless you have a piece of Teflon tubing handy.) Wrap it with bare magnet wire using a fairly heavy gauge. Lay the wraps down perfectly with each against the previous. Silver solder over the whole shaped coil. Extract mandrel. File, fill and paint. Windy U. sold molded plastic exhausts for his Spitfire project. No tubing involved. Less fidelity, but less headache….

Best of luck. Show us how it turns out!

Dave


Looks like Sparky beat me to the send button. Where there's Sparks, there's Lightnin'

Offline Gary Dowler

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 1017
Re: Bending Aluminum Tubing
« Reply #9 on: February 03, 2019, 03:54:21 AM »
This is a product commonly used by gunsmiths to make chamber castings. It's very easy to work with and has a melting point between about 160-190 deg, depending on exact alloy. It expands very little after casting.  Would be easy to pour into a warmed up aluminum tube, then after bending just heat again with a hair dryer to remove it.

https://www.brownells.com/gunsmith-tools-supplies/barrel-tools/barrel-chamfering-accessories/cerrosafe-chamber-casting-alloy-prod384.aspx
Profanity is the crutch of the illiterate mind

Offline Dave Hull

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1901
Re: Bending Aluminum Tubing
« Reply #10 on: February 03, 2019, 12:52:17 PM »
Joe,

Which version are you modeling? On at least some -190's the stacks hardly show. These had the DB801 engines. See a picture of the A-8 pipes below.

     http://www.ipmsstockholm.se/home/wp-content/uploads/2012/05/detail_bmw801_52.jpg

If it is a -D, with the Jumo engine, then I see your problem....

     https://www.bing.com/images/search?view=detailV2&id=EEEDF1DD5A7D1C3124F02F4305AD6280EF94D32F&thid=OIP.EAcb7SyCPwh9CAdzALBJkAHaEo&mediaurl=http%3A%2F%2Feshop.scalehobby.eu%2Ffotky6453%2Ffotos%2F_vyr_47REXX48022-01.jpg&exph=500&expw=800&q=FW-190+exhaust+pipes&selectedindex=9&ajaxhist=0&vt=0&eim=1&ccid=EAcb7SyC&simid=608007710869749924

Kind of a pain, but if you can't get the radius, I'd consider going back to brass and cutting v-notches on the inside of the intended bend. Bend as much as you can before notching, then complete the bend, and solder. Another idea to kick around. Or go the Windy route and mold them. You might also consider a thermoplastic tube. Slip over a piece of O-ring material, heat, bend, extract o-ring. This might work pretty good and be less work.

Good luck!

Dave

Offline Tim Wescott

  • 2016 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 12804
Re: Bending Aluminum Tubing
« Reply #11 on: February 03, 2019, 12:53:57 PM »
... Or go the Windy route and mold them. ...

Or get all modern and 3D print them.
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline katana

  • Trade Count: (0)
  • Commander
  • ****
  • Posts: 161
Re: Bending Aluminum Tubing
« Reply #12 on: February 03, 2019, 02:05:09 PM »
I'd be tempted to try the old plumbers bending spring trick - 18" long, tight wound steel spring inside the copper pipe to be bent and then bend round a mandrel or a knee. A spring on the outside can still allow a kink to form and push out past the spring coils. Dunno if it'll work but anything is worth a try............maybe?

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13716
Re: Bending Aluminum Tubing
« Reply #13 on: February 03, 2019, 02:30:23 PM »
I'd be tempted to try the old plumbers bending spring trick - 18" long, tight wound steel spring inside the copper pipe to be bent and then bend round a mandrel or a knee. A spring on the outside can still allow a kink to form and push out past the spring coils. Dunno if it'll work but anything is worth a try............maybe?

   Several people make those springs (both inside and outside springs) in hobby sizes. Every time I tried to use them, the tube kinked anyway, and the spring was both hard to remove, and damaged where the tube spread them out and left a kink in them, even after I annealed the tube completely.

   What we need is some sort of mandrel bender, but I haven't had the time to design and build such a thing. I have seen the larger types in use- I had to fabricate some 1 1/4" aluminum tubes that go through the chassis of my old Lotus to carry coolant from the engine to the radiator and back. My repair shop had tried, unsuccessfully, to bend them in a variety of ways, but  I found a place in San Jose that had a mandrel bender, and it made an absolutely perfect 9" radius bend in a 1 1/4" 5052 T0 aluminum tube, looked like it was somehow molded into that shape, constant diameter, pristine in every regard. Took him about a minute to set up the machine and 5 seconds to bend it, $10.

    Brett

Offline Dave Hull

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1901
Re: Bending Aluminum Tubing
« Reply #14 on: February 03, 2019, 03:17:01 PM »
Joe,

I just measured the shop-made tool I used to form the 1/4" tubing. It has a 3/4" radius. I can text you a picture of it if that helps. To Brett's point about a mandrel bender, if you added more features to this simple form-tool, that is all it would take. A wiper die, some clamps, and the mandrel all on a frame. But that raises the usual question:  are we making airplanes, or are we spending all our time making tools....   For something special, sometimes ya gotta do both.

Dave

Offline Avaiojet

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 7468
  • Just here for the fun of it also.
Re: Bending Aluminum Tubing
« Reply #15 on: February 03, 2019, 07:18:02 PM »
They already have aluminum tubing that's pliable and easy to bend even small tight bends.

You just have to find a HDWE store that knows about it or a supplier.

Sold in loops and the HDWE store cuts what you need.

I've had this .25 od stuff for years. I used it for the exhaust on radial engines for scale projects like my Sikorsky S-39. I think that was 5" in diam. or so? I played with the ends, it'll bend tight.

Comes in many diameters.

 
Trump Derangement Syndrome. TDS. 
Avaiojet Derangement Syndrome. ADS.
Amazing how ignorance can get in the way of the learning process.
If you're Trolled, you know you're doing something right.  Alpha Mike Foxtrot. "No one has ever made a difference by being like everyone else."  Marcus Cordeiro, The "Mark of Excellence," you will not be forgotten. "No amount of evidence will ever persuade an idiot."- Mark Twain. I look at the Forum as a place to contribute and make friends, some view it as a Realm where they could be King.   Proverb 11.9  "With his mouth the Godless destroys his neighbor..."  "Perhaps the greatest challenge in modeling is to build a competitive control line stunter that looks like a real airplane." David McCellan, 1980.

Offline Trostle

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3338
Re: Bending Aluminum Tubing
« Reply #16 on: February 04, 2019, 09:18:45 PM »
Unless you are trying to do the thing for 100% scale, just carve some basswood pieces to resemble the non-round portion of the stacks that actually protrude from the nose of the model.  That would look better on a semi-scale FW-190D than would round tubing bent at a ridiculous angle. Can be effective if done right.

The cross section of the 190D exhaust stacks are rectangular with rounded corners.  Using "bent spaghetti" round tubes for exhaust stacks like on a Mustang or the late model Spitfires would not look right.

Keith
« Last Edit: February 05, 2019, 11:55:42 AM by Trostle »

Offline JHildreth

  • 23 supporter
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 162
Re: Bending Aluminum Tubing
« Reply #17 on: February 05, 2019, 03:12:16 PM »
Thanks to all who have responded.

Keith, thanks for your input.  None of the pictures that I have show enough detail to clearly see the shape of the stacks.  Now that I know what to look for, one of the three-views that I have kinda shows the rounded rectangular shape, but it isn't obvious.

I was intrigued by Tim Wescott's response about 3D printing and I have been researching that avenue.  I have found a couple of businesses close by that provide 3D printing services to the public and have been searching for the appropriate software for generating the printing (.stl) files.  This approach appeals to me if it does not turn out to be too expensive.

Again, thanks for everyone's input.

Joe


Offline Robert Whitley

  • 21 supporter
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 287
Re: Bending Aluminum Tubing
« Reply #18 on: February 05, 2019, 03:42:33 PM »
If you go the 3D printed route you might want to see if your local library offers this service.
Ours does and all they require is the file which you might find in the public domain.
Our library only charges the material cost.
Good luck.

Offline Dan McEntee

  • 23 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 6824
Re: Bending Aluminum Tubing
« Reply #19 on: February 05, 2019, 04:38:36 PM »
   I have made a mold of the exhaust stacks that come with the old Midwest war bird series planes, and used that as a form for vacu-forming replicas. I filled the kit piece with model railroad hydrocal that is used for making scenery. Much better than plaster and the form is ready to use right out of the box. I used my Mattel Vacu-Form toy to make them. This was quite a long  time ago and I don't know if I still have the form. You could carve one from bass wood and if it is symmetrical you can make right and left side exhausts. Even made out of .030" heavy plastic it should weigh next to nothing.  I'll have to look into that again for a future project.
   Type at you later,
   Dan McEntee
AMA 28784
EAA  1038824
AMA 480405 (American Motorcyclist Association)

Offline Howard Rush

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 7805
Re: Bending Aluminum Tubing
« Reply #20 on: February 05, 2019, 05:10:30 PM »
I was intrigued by Tim Wescott's response about 3D printing and I have been researching that avenue.

Joe,

Did you get my PM?
The Jive Combat Team
Making combat and stunt great again

Offline Larry Renger

  • 21 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3995
Re: Bending Aluminum Tubing
« Reply #21 on: February 05, 2019, 08:58:49 PM »
How about macaroni? It may be the right size and shape.
Think S.M.A.L.L. y'all and, it's all good, CL, FF and RC!

DesignMan
 BTW, Dracula Sucks!  A closed mouth gathers no feet!

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13716
Re: Bending Aluminum Tubing
« Reply #22 on: February 05, 2019, 09:49:19 PM »
How about macaroni? It may be the right size and shape.

  That's a very good solution, I have used macaroni of various types as tubes on scale projects several times. It's pretty tough, you have a wide variety of possible shapes, and admirably cheap. Its also very easy to work, in this case, to easily thin the end of the tube to make it seems thinner.

    Brett

Offline Trostle

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3338
Re: Bending Aluminum Tubing
« Reply #23 on: February 05, 2019, 10:16:03 PM »
How about macaroni? It may be the right size and shape.

It still has a round cross section and that is not right.

Keith

Offline Brett Buck

  • Trade Count: (0)
  • Admiral
  • ******
  • Posts: 13716
Re: Bending Aluminum Tubing
« Reply #24 on: February 05, 2019, 10:34:53 PM »
It still has a round cross section and that is not right.

  Not if you boil it for a while....  I am not kidding, that will work.

    Brett

Offline Dave Hull

  • 24 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 1901
Re: Bending Aluminum Tubing
« Reply #25 on: February 05, 2019, 11:51:07 PM »
Look guys--he's not building a Caproni or a SIAI-Marchetti here. There wasn't any pasta in Germany in those days....

(Actually, it took all my willpower to avoid suggesting macaroni. It was in every other magazine's helpful hints back in the day....  But then Larry had to go there with Brett "noodling" him on.)

It would appear that Joe is working on a D-model. On the other marks, with the DB801 engine, you can just barely see the ends of the exhausts flush with the trailing edge of the cowl flaps. And of the D's, it seems that there is at least one version with separate stacks, which may be what he is going for, but there is also the version with common collector pipes, which would be easier and still look good. I think that is the version that Keith showed.

What would have the maximum coolness factor, is the separate ejector stacks that are actually functional. That's my vote. And the hardware store aluminum would be the way to go. Wonder what it would sound like? And for sure, you wouldn't need fake exhaust staining. You'd get the real thing. That's gotta be good for a couple more appearance points.

Divot McSlow

Offline JHildreth

  • 23 supporter
  • Trade Count: (0)
  • Commander
  • *
  • Posts: 162
Re: Bending Aluminum Tubing
« Reply #26 on: February 11, 2019, 07:54:16 PM »
OK folks, especially Tim Wescott and Keith Trostle.  Here is what I decided to do regarding the exhaust manifold.


I have found a couple of businesses here locally that offer 3D printing services and will be giving it a try.  It won't be as cheap as fabricating the manifold out of balsa and tubing, but it should look a bunch better.

Thanks to all for your responses.

Joe

Offline Trostle

  • 22 supporter
  • Trade Count: (0)
  • Admiral
  • *
  • Posts: 3338
Re: Bending Aluminum Tubing
« Reply #27 on: February 11, 2019, 11:24:25 PM »
  Here is what I decided to do regarding the exhaust manifold.

I have found a couple of businesses here locally that offer 3D printing services and will be giving it a try.  It won't be as cheap as fabricating the manifold out of balsa and tubing, but it should look a bunch better.


Joe

I think you are going in the right direction.

Keith


Advertise Here
Tags:
 


Advertise Here