Old School Chopper Frame Fabrication - Knucklebuster

Figure 1
You can cut these slots with a reciprocal saw, a saber saw, a hack saw or with a small grinder fitted with a very narrow
abrasive disc but the objective is to make the cuts very straight and just ever so slightly to narrow for the plates to slip into
without doing some fine-tuning and touchup grinding or filing. To start with deliberately cut the slots a little to short and as
you're fitting the fitting the plates into their final position deepen the cuts as necessary to insure a good tight fit while keeping
the plates plumb and square to the frame and the axle axis.
Figure 2
Figure 2 is a snapshot of a plate slot in progress that was cut with a abrasive disc on a small grinder. It's pretty rough at this
stage but we'll dress it up as it's deepened to fit the axle plate. The only really critical thing at this point is to keep the
centerline of the notch parallel to the frame rails in the longitudinal direction and square and plumb with the frame centerline
in the transverse or horizontal direction.
Fitting the axle plates is one of the most laborious steps you'll probably ever undertake when building a cycle frame and I
cannot over emphasize how important it is to take great care in setting up the alignment of the plates since in effect they
determine to a great extent the overall handling characteristics that your frame will inherit. Axle plate alignment is so
important in fact that many shops build their entire jig around the plates and work forward with the rest of the frame work.