Cut the straight frame members with
a chop saw. For ends that will be welded to
other tubes, use a tubing notcher or milling
machine to cut fish-mouths to fit (Figure B).
You can bend curved pieces made out of
EMT or other lightweight tubing using a hand
tube bender. On my frame, this included the
rear harness cross-member, the 2 upper rails,
and the 2 upper cross-members that hold the
steering shaft. For the heavier roll bar, I used
a hydraulic bender.
Weld the frame together. With EMT, sand
off the galvanized surface layer where you’re
going to weld, as it can weaken the joint.
Where suspension components, brake plates,
and other parts attach to the frame, weld
on tabs or tube stubs rather than cutting or
drilling the tubes, which will make it weaker.
Give it a test fit (Figure C). Be sure to make
car engine noises to pretend you’re going fast!
For both front and back suspensions I used
62 Make: makezine.com/26
an unequal length A-arm design, which means
that 2 pivoting horizontal arms connect
each wheel to the frame, with the upper arm
shorter than the lower one. This gives the
wheels negative camber at bump and positive
camber at droop, maximizing their contact
with the road while cornering.
The shock absorbers bypass the upper
arms and only attach to the lower arms,
which need to be beasts because they bear
the load of the entire kart. In back the shocks
connect up to the sides of the roll bar, and in
front they angle in and connect to a bracket
sticking up from the middle of a horizontal
frame member (Figures D and H).
The suspension arm pairs are mounted
to the frame via 2" rods that rotate inside
horizontal bushings welded to the frame. Both
rods and bushings are made of higher quality
steel so the arms swing up and down precisely,
without moving side to side. At the wheel end,
the arms connect to ball joints attached to
the top and bottom of the kingpin (Figure E),