Old School Chopper Frame Fabrication - Knucklebuster

Figure 1
In Figure 2 we see the more common design where the down tubes are welded onto the lower portion of the steering neck.
Figure 2
People will argue all day about the various pros and cons of either type of design but basically the reasoning goes that the old
design puts less bending stress on the neck tube proper. In other words the tube itself is not subjected to a bending load and
isn't really a structural member of the main frame. The more modern design actually makes the neck tube a structural frame
member and when loads are applied from the backbone or the down tubes the neck is subjected to a bending load.
When one considers the wall thickness of the typical steering neck I doubt whether either design type has a structural
advantage or disadvantage over the other.
I personally think that its easier to fabricate the type of connections shown in Figure 2 but having built frames the old way for
so long I'm kind of stuck in my habits. One big advantage of building frames the old way however is that the neck rake angle
can be very easily changed without messing with the down tubes. This is a very practical feature as it allows you to re-chop a
Chopper if you want to change its appearance or handling characteristics later on. Additionally it is easier to straighten a
frame built with the old style of neck connection if it ever gets banged up in an accident.
All of the plans, diagrams and photos of our projects are intended to be fabricated using what we've called the old-style neck
connection. If you opt to build it the other way you will have to make changes in the down tube angles and dimensions.
In part four of this series we bent the forward portion of the lower rails that created the down tube section and now we've got
to create the joint where the two down tubes connect at their uppermost end.
Figure 3