Pipe vs Tube
Advantages of Framing Material For Karts and Bikes
When building your own go kart or mini bike frame, you'll probably like smooth bends rather than a squared off design. However, bending materials requires special tools. We'll look at the two best ways to do this: using a pipe bender and using a tubing bender.
Pipe vs Tube
Round pipe is commonly available even at your local hardware store. Tubing is available at your metal supplier. Price the material beforehand, and steer clear of seamless tube (aka DOM, drawn over mandrel). It is very expensive.
Tube is called out by the outside diameter (OD). A 1" round tubing will be exactly 1". Tube is available in thin wall (0.065") and thick wall (0.125"). To find the inside diameter (ID), double the wall thickness (ie .125x2=.250") and subtract from the OD.
Pipe is called out by its inside diameter rather than its outside diameter. Therefore a 3/4" pipe will actually measure 1.05" OD. A 1" pipe will measure 1.315" OD.
Though the pipe is called by the inside diameter, the actual ID is slightly greater. A 3/4" schedule 40 pipe has a wall thickness of .113". The ID is therefore .113"x2=.226". 1.05"-.226"= 0.824".
Why Doesn't Pipe's Real ID and Called ID Match?
Advances in pipe making are to blame for the mismatch between the called out size and the actual size. Old pipe was weaker than today's pipe, and to perform at the rated pressure had to have a thicker wall than is necessary for modern pipe.
But if the OD size of pipe was shrunk, new pipe would be too small to fit old pipe fittings. So the wall thickness became thinner and the ID increased.
Cost of Bending Material
A tubing bender is quite expensive, starting around $500, and likely includes only one sized bending die. You'll need to purchase more dies to bend other sizes of tube, and these can run at least $200 each.
On the other hand, a hydraulic pipe bender can be found often for around $70 that includes all the bending dies you'll need.
Type of Bends Possible
Tubing benders are more more elegant than pipe benders. Cheap pipe bender will only do around 100 degrees maximum bend, whereas a tubing bender may do a full 180 degrees.
However, 180 degree bends can be accomplished with the pipe bender by welding two 90 degree sections together.