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