Be aware that you want a strong but light frame.
We suggest 1/8" thick tubing, either square or round
(or both) depending on preference. Most of the store-bought karts use thinner walls, and the life of the cart surely won't be as long.
You may also use 1"x1/8" angle iron. A benefit to this material is that making bends is very easy -- you can notch one side, heat, and bend. By adding filler material to the notched area you restrengthen the frame.
Since it's more difficult to bend square tubing, many people
use a mixture of square and round. When laying out the design,
consider this: welding round to square is much easier than
welding round to round. To weld round to round you'll need
to prep the tubing by cutting a rounded edge on the ends with
a hole saw. Another way is to heat the round tube and flatten
the ends to attach to another round tube, but you're sacrificing
looks and strength if you do this.
If you don't understand
what we mean about the difficulty of welding round to round
tubing, just put two pieces together and note that you have
to cut a crescent from one to attach flush with the other.
You can do this with the grinder, but it's tedious work.
Scrounging for parts can also save you some money. Lawn equipment often use parts that are perfect for adapting to a go kart: gas tanks, steering wheels,
tie rod ends, parts out of the rear axle (inspect it for strength!), tires & wheels,
pulleys, variable speed clutches and so on.
Cutting Your Materials
If you're using a chop saw, a handy way to ensure you get two pieces of tubing exactly the same length is to use vise-grips to keep two pieces together. It saves time, too!
If you don't have a chop saw, circle saws will accept abrasive blades, or you can use the old standby, the hacksaw. If you haven't bought a new blade in a while, now is a good time.
Make all your cuts first so that you can lay out the frame
completely before welding. At this point you'll know if something
isn't working, and can fix it before it eats up time later. If you are doing your own welding this is less of a major concern, because you can adjust things as needed. But if you're getting a someone else to do the welding for you then they will greatly appreciate that everything is ready to go.
Check Harbor Freight for inexpensive benders,
but remember they won't usually bend square tubing. The cheap orange bender, called the "Hydraulic Pipe Bender" is for pipe, not tubing. However, 1" tubing is just about the same size as 3/4" pipe, so it might work for that size. If nothing else, you could use pipe for the bent sections and tubing for the other sections.
Angle iron could also be used for pieces that need to be bent. Cut one side of the iron, heat and bend, then fill in the gap with filler metal.