Making exhaust stacks

[Fat Brian]

How do you bend aluminum tubing without it kinking? I need some 45 degree bends and they're flattening out really bad. I'm thinking about making a wooden form with a deep groove in it to keep the sides of the tube from spreading out but I'm not sure it will work.

[High octane]

I heard that guys insert a rod inside the tubing before making the bend, and this should prevent the tubing from kinking. The rod should be pretty much the same size of the I.D. (inner diameter) of the tubing. Then after you make your bend, you remove the rod. I hope this helps.

[Aaronw]

A tubing bender helps a lot. The simplest are springs you insert the tubing into, more complex ones have a grove or a hinge like mechanism. They help support the tubing and spread the forces.

You can also fill the tubing with sand or similar and cap the ends to keep it in place while you make your bend.

Using a curved piece like a dowel to bend the tubing around can help keep you bend straight and help support the tubing to prevent kinking.

[Ace-Garageguy]

I heard that guys insert a rod inside the tubing before making the bend, and this should prevent the tubing from kinking. The rod should be pretty much the same size of the I.D. (inner diameter) of the tubing. Then after you make your bend, you remove the rod. I hope this helps.

Unfortunately, there's no way to get the "rod" out after you bend the tube. The tube will collapse enough to clamp the rod securely inside forever. The only decent results I've had with this method is to use plastic rod that is, like Nick suggests, very close to the ID of the tube you're trying to bend. Position a short piece of rod where the bend will be, so you can't see it inside the stack after it's bent and cut to final length. You'll need to think and experiment, because the tube will naturally try to bend and collapse where the inserted rod ends. Cut to final length AFTER you bend it, by the way.

A tubing bender helps a lot. The simplest are springs you insert the tubing into, more complex ones have a grove or a hinge like mechanism. They help support the tubing and spread the forces.

You can also fill the tubing with sand or similar and cap the ends to keep it in place while you make your bend.

Using a curved piece like a dowel to bend the tubing around can help keep you bend straight and help support the tubing to prevent kinking.

For these small diameter tubes, I've NEVER had good luck with the spring-type wire-wound benders on any kind of sharp radius. They simply are not strong enough to support tubing bends sharp enough for stacks and headers, usually. They also get bound-up on sharp radii and are almost impossible to remove without damage.

And sand is simply too coarse to do you any good on very small diameter tube. It IS possible to fill small tubes with molten "fixturing alloy", let it harden, make your bend, and melt it out again. Kind of a PITA for model work, but you can buy it here. http://www.use-enco.com/CGI/INSRIT?PMAKA=505-3877&PMPXNO=949471&PARTPG=INSRHI

I've READ that filling the tube with water and freezing it will prevent kinking, but I have NOT tried it. It's worth a shot.

The lever type benders will work...to a point...but are difficult to find in sizes small enough to work with scale model car tubing. I routinely use this type forming brake and fuel lines on real cars, but only down to 1/4 or 3/16 inch diameters.

This one from Harbor Freight will bend down to 1/8 inch, but you see how it's not a tight radius that you'd need on a model car exhaust or intake stack. I've been getting around to machining a much smaller version of this to experiment with, but haven't so far. This is the idea. http://bbs.homeshopmachinist.net/threads/24051-A-tube-bender-saga You MAY be able to find a commercial one that will work on small stuff, but I haven't yet.

You'll have a MUCH easier time forming your parts from solid styrene rod (and drilling the ends if you need them to appear to be tubing) or solder.

This is a bench version (NOT MY DESIGN OR WORK) of a simple tool for bending fairly sharp radii in small tube also. The pin sticking up secures the tube, while the lever rolls the bend around rollers. Not so hard to make if you only need one radius and one diameter.

Edited March 2, 2015 by Ace-Garageguy

[fantacmet]

For exhaust stacks drilling the tips is what we are trying to avoid, as that's what the kit parts are. The alloy is a good choice. You might be able to find it a bit cheaper from a firearms place though. Check Numrich gun parts or Cheaperthandirt.com. Stuff is nice and strong too. For removal if you are worried about discoloration, you can drop it in a pan of water and bring it to boiling, then pick the part out with tweezers, let it drain into the pan, let the water cool and scoop out your now solidified metal. I'm lucky enough if I really need to use any I'll just go to a friends house and use his. I like the idea of the small bender there made basically with two pulleys it looks like. I've got a mill I might have to try making one.

[Fat Brian]

These are what I'm wanting to replicate.

http://flipacars.com/photos/GMC/87/a8/10748_flickr-the-gmc-chevy-generals-bisons-astro-titans-crackerboxs.jpg

Bill, I'm wanting try to build something like that tubing bender you have but that will make tighter radius bends. I wonder if I could find solder big enough to fit in a 3/16 or so tube?

[snacktruck67]

I use the spring type benders, and I have had great success with them. You can pick up a set of 4 at Hobby Lobby for under $4.00 with the 40% coupon.

Edited March 2, 2015 by snacktruck67

[highway]

These are what I'm wanting to replicate.

http://flipacars.com/photos/GMC/87/a8/10748_flickr-the-gmc-chevy-generals-bisons-astro-titans-crackerboxs.jpg

Bill, I'm wanting try to build something like that tubing bender you have but that will make tighter radius bends. I wonder if I could find solder big enough to fit in a 3/16 or so tube?

Honestly I would suggest buying a set. I know that Rhino's Model Truck Parts on Facebook sells those style 45 pipes in stainless steel, and shouldn't run you more than $10. I have had my eye on a set of his 8" diameter stacks like that for one of my projects. Those are normally 5" diameter for stock stacks, but he does do custom orders also, so he might be able to make you a set. I'm on my phone so I can't give you a link, but i'll post one next time I'm home and not in the big truck LOL!

[fantacmet]

Bill, I'm wanting try to build something like that tubing bender you have but that will make tighter radius bends. I wonder if I could find solder big enough to fit in a 3/16 or so tube?

While i'm not Bill, yes you can find that size solder. Look in the welding section of your local hardware store.

[Bennyg]

How do you bend aluminum tubing without it kinking? I need some 45 degree bends and they're flattening out really bad. I'm thinking about making a wooden form with a deep groove in it to keep the sides of the tube from spreading out but I'm not sure it will work.

I use k&s pipe bending springs. I heat the pipe up and place a spring inside and out side and only bend a bit at a time With the aid of a piece of dowel. After you have bent the pipes, sand them smooth and polish them with metal polish. Make sure you don't heat the bending springs, I've killed a couple that way. Hope this helps.

Here is the results.

http://www.modelcarsmag.com/forums/index.php?showtopic=77442&hl=%2Bkenworth+%2Bt904

http://www.modelcarsmag.com/forums/index.php?showtopic=98361&hl=%2Bkenworth+%2Bt904

Ben

Edited March 2, 2015 by Bennyg