HammerHead Trike - Page 2 of 7
When you have both head tubes welded to their two 12-inch extension tubes, it's time to weld them to the original head tube on the donor frame.
As shown here, the extension tubes are welded to the original head tube so that all head tubes are at the same angle and so that the extension tubes are at 90 degrees to the frame tubing. You want each head tube to end up at the exact same angle as the middle head tube so that the caster angle remains the same as it was on the original bike. If you imagine two identical bikes standing side by side, then you can picture what we want here.
At this point, just make a few good tack welds around the joints to secure all of the pars together. A final alignment check will be made by installing the forks and front wheels to compare them with each other.
To ensure that the two head tubes are aligned with each other, put the bearings, rings, and forks on both sides and then install the two front wheels. Remember that both front wheels must be the same diameter, which is why both tires should be the same type. When you have both wheels installed, stand up the bike and place both forks in the straight ahead position for a visual inspection. With the parts only tack welded, you can probably make slight alignment adjustments by tapping with a mallet.
Once you are certain that both head tubes are aligned, weld around all of the joints, following the same order of welding on both sides so that any distortions happen equally.
To make this frame structurally sound, a set of trusses will be added to the front in order to triangulate the frame. The frame is somewhat rigid as it sits, but any hard force to either front wheel could bend the frame at the joint between the head tube and the new extension tubing.
With some simple trussing, we form a triangle on each side, making the frame extremely strong. Any tube with a diameter between half an inch and 1 inch will do for the trussing. I found some old lawn furniture with 3/4 inch tubing and cut a few pieces to make the trusses.
These trusses are welded from the top of each head tube to somewhere near the middle of the top tube on the main frame. The trussing should be installed a few inches ahead of where your knee will be when you are pedaling the bike. To find this spot, put on a crank arm and set the seat to your height, then mark it on the frame while you pedal. The main goal is to make sure your knee does not hit the tube.
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You can build it yourself from our easy to follow DIY plans!