Bending Thin Wall Tubing for Bicycles and Furniture - Poor Man's Mandrel Bender





Introduction: Bending Thin Wall Tubing for Bicycles and Furniture - Poor Man's Mandrel Bender

About: Aerospace welder and party animal

One of the biggest problems about bending tubing in the DIY world is wrinkling in the corners when bending past 45 degs on Thin wall tubing...

Tradeoffs often are needed just to get the bends needed such as

- going to thick wall tubing and linking it to other thin to keep some of the weight down

- making the whole project out of thick wall heavy tubing, which we know that no one wants a 10+ pound bicycle frame or 15 pound chair just because you wanted a neat roll or bend in it.

I have been an aerospace prototype metal fabricator for 10+ years now and I want to show you some tricks of how you can you tackle this with some simple tools you may already own...

Time for a link to my blog if you want to know more about what I do and tips about metal fabrication.

Step 1: What You Need...

1. A bender with the correct bending die - for this project I will be using a low priced JD2 bender with a 1" die

( if you don't need a tight bend then a roller may work as well, this is a small Harbor roll bender with a 1" die )

2. You will need your tubing material and a hole saw with a inside diameter the same as the outside diameter of the tubing. You will use the hole saw to cut plugs to cap the tubes - that's what the little square of 16+ gauge sheet metal is used for, cutting the plugs out of. .

( for this demo I will be using drop pieces from a local laser cutter, they give them to me because they will be scrap with no use to them, it may be worth your time to call around to water jet or laser cutters in the area)

3. Sand for a sand blaster ( fine grit ) and a funnel with a spout that fits inside the tubing.

Step 2: Cut Your Tubing and Weld on End Cap

The size of tubing doesn't matter as long as you have the end caps the correct size and you have the bender die to make a good bend. These things are VERY IMPORTANT because if you don't have the correct die it will not matter how much sand you put in it because it will squish, the die holds the tube 180 degs to control the shrinking and stretching of the tube, if it only contacts on a fraction of that half of the die it will not bend correctly.

The tube should be longer then what you need because of the additional end cap and need for possible cutting and bend clearances ( your situation may very)

Apply the cap and weld - ONLY on 1 end , you will need the other end open to put sand in.

It is best to do a 360 degree weld and I like to tig weld them to keep the weld small so it doesn't affect the bender with loading and unloading due to a giant weld but its not necessary to tig weld the end caps, mig, brazing or other arc processes are ok, just as long as you have a good hold on the end cap.

Step 3: Add the Sand !

This is a very important step that sometimes people rush.

When adding the fine sand make sure you pack the tube by hitting it in some way to make it settle

The level of sand sinks due to it packing tighter in the tube, keep adding sand until its flush with the top and you feel it can't be packed any tighter.

Then place the cap on it and weld it on just like in the last step.

TIP - always keep the tube vertical during welding.... trust me... its not fun when sand is pouring out and your trying to weld it. Use of a bicycle repair stand is perfect for this operation.

Step 4: Bending Time

Keep the dies oiled on the bender if you have a drag style bender, this will help move it along and save life on your dies

As I was talking about in a few steps back, it is very important that the correct die be used for the tubing to provide near 180 degree support of the inside bend radius during bending. This part of the tube is shrinking while the outside of the tube is stretching, if there any room on the sides that's where the tube will go leaving you with a Egg or oval shape.

Step 5: Cut the End Caps Off and Drain the Sand

That's a nice bend that is near perfect without much material movement on a piece of .065 steel tubing.

Cut the end caps off with a cut off wheel or chop saw.

DO NOT - Cut the tubes open where sand should not be like on a milling machine or cold saw where the sand can get back in to the oil system or coolent.

Drain the sand in to the container again to use for the next time.

Step 6: Enjoy

Time to build



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    26 Discussions

    For small tubes one can fill with solder, make the bend then heat to melt the solder out.

    2 replies

    Thanks for the tip, I used solder because of a very short bend on 1/8 SS pipe on a few parts.


    4 years ago

    If you are using seamed tube always put the seam facing the die. it will stretch the weld less and there is less chance the tube will deform.

    1 reply

    I liked your write up I learned a lot

    wat abut pouring water an freezing it. depending on yr methods that may work as well.

    1 reply

    When I do water freezing, its mostly for Titanium and other metals because there is no risk of sand contamination in the next steps like welding so I won't do sand for that reason.

    The time it took me to do this little demo was about 20 minutes compared to water freezing which can take a few hours if your lucky. If you can use sand its the quickest and easiest out of all of the methods. Thanks I forgot to add that about the ice method.

    This will be my first time bending pipe, and I'm pretty nervous. For a first-timer would you recommend hiring a tube bending service? I've gotten some of the tools together, and my husband knows how to solder.... I'm just nervous that the tube will snap, or break and hurt one of us. Any pointers?

    1 reply

    I came across these guys who do mandrel bending. You may have better luck there!

    Great pictures and excellent desciptive writing. Good job, thank you.

    Thanks for the tips, I've got a store of thin wall tubing (.035" wall 1" DOM 4130) and will look forward to doing this for the next bicycle trailer.

    Would filling the tube with water work? It's incompressible and it won't get grit into anything delicate. Or would it complicate welding?

    3 replies

    When they bend pipes for trombones I believe they fill the pipe with water and freeze it so there's ice inside when bending.. I can't remember exactly but with that method you shouldn't need to weld or braze the ends..

    Although there is a way to do it with water which does not involve welding. If the pipe is threaded on both ends (threading pipe isn't difficult, although you need a specific tool for it), just use pipe caps to seal the ends. This way, you don't have to cut off the ends to get the water out later, either.

    If you use water it will turn to steam when you weld it, pressurising the tube with the possibility of turning it into a pipe bomb...

    We don't use either. I can't remember the formulation we have, but its a number not a name.

    Bend looks 'necked.' It would be unacceptable for a kart frame.

    Why would you need sand if you have a good bender like that one?

    It should work without sand. But that's why I prefer one with at least a traveling block.