Old School Chopper Frame Fabrication - Knucklebuster

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Once the pattern is cut it can be used as a template to scribe around on the 3/8" cold-rolled stock used to fabricate the adjuster plates or it can be used to make a wooden 'follow' block if you're going to plasma or flame cut the material. We prefer doing this type of work on a Band saw so we simply transferred the pattern directly to the steel. Figure 15 The rough cut plates are shown in Figure 15. The slots for the axle tube were cut on a milling machine but they could have been done with a drill press using multiple passes cleaned up with a little grinding. As you can see we deviated from the patterns inside cut on the final product and made a nice large radius that matched one of the ideas we sketched out on the original cardboard pattern shown in Figure 14 only because it ended up being easier to make on the band saw. For this project we're using a 3/4" axle and the slot is configured for a 2" range of total adjustment. The plates ideally should be installed in such a manner so that the axle is positioned closer to the front of the slot when the chain or belt is initially installed so you have plenty of room for rearward adjustment as time goes by. I try to mount then so that there is about 3/4" of forward adjustment and 1.25" of rearward adjustment. This gives you enough room to bring the axle all the way to the front to install a chain. Of course if you're installing a belt you have to pull the axle anyway but once it's on the pulley you'll still need some wiggle room on the front side which brings us to another matter. As we've mentioned before there is no 'standard' measurement between the tranny and wheel sprocket or pulley on a chopper so this dimension is usually set during the frame mockup stage to match the chain link or belt nib count you're planning on using. For those interested we've measured several types of frames and this dimension ranges from as short as 19 inches to as long as 23 inches. On our rigid frames this distance is usually 21.625 inches. For those of you wanting to run belts I strongly suggest that you use a 136 nib belt as they're now the defacto standard on most factory bikes. The original 4-speed drive belts used 125 nibs, being about 1.375" shorter (installed) than the newer five speed setups. For those of you wanting to do this without the benefit of a real mockup you can figure that one link or nib equals roughly .2" of horizontal axle movement using average sized sprockets. Here are the axle plates finally cut from the template we made in Part 8. I've slid them on the dummy axle shaft just to check that they line up with the angles of the tubes.
Figure 1 You'll no doubt realize that we haven't installed the rear transmission mount cross member yet and we need to do so just before we do the actual installation of the axle plates but we've left this pretty critical part of the frame fabrication until this late point in the build-up so we have a final chance to do some frame straightening before we button it up at the rear. Chances are that unless you have a pretty good tubing bender and an accurate jig that the ends of the lower rails and the ends of the upper wishbones don't exactly line up vertically if you're looking at the frame from the rear as seen in figure 2. Figure 2 Actually this photo was taken after we straightened the lower right tube that was about 1/8" off center and had already tacked the transmission cross member in place. The short focal length camera lens and our poor setup for a vantage point in this shot makes the frame look pretty out of whack but it isn't.
Page 1 and 2: Old School Chopper Frame Fabricatio
Page 3 and 4: 1. Steering head. Also called the s
Page 5 and 6: Figure Error! Bookmark not defined.
Page 11 and 12: Figure 11 This cross member sets th
Page 15 and 16: Figure 15 Figure 15 shows the end r
Page 17 and 18: Figure 17 There is a corresponding
Page 19 and 20: Figure 19 I call this area of the f
Page 21 and 22: Figure 23 The slope angle of the 'r
Page 23 and 24: In Figure 3 we can see the two tube
Page 25 and 26: Figure 1 shows the basic components
Page 27 and 28: an eighth of an inch clearance betw
Page 29 and 30: Figure 6 In Figure 6 we've deepened
Page 31 and 32: Figure 2 if you look closely you ca
Page 33 and 34: angle finder. It explains is easy t
Page 35 and 36: Figure 6 In this shot I've propped-
Page 37 and 38: In case you're interested I messed
Page 39 and 40: Figure 3 Figure 3 depicts a plate t
Page 41 and 42: Figure 7 Figure 7 is another 'boxed
Page 43 and 44: Regardless of the style or type of
Page 45: Figure 13 At this point all you nee
Page 49 and 50: Figure 4 Actually the plate will be
Page 51 and 52: If you're building a frame without
Page 53 and 54: Figure 5 Now that the plates are in
Page 55 and 56: Figure 2 Clean the notch up slightl
Page 57 and 58: Figure 5 The frame in Figure 5 is o
Page 59 and 60: Figure 7 The tube in Figure 7 above
Page 62 and 63: We'll now begin doing the detail wo
Page 64 and 65: The charge has been removed from th
Page 66 and 67: Some people have reported problems
Page 68 and 69: Steering Necks For some unexplained
Page 70: Figure Error! Bookmark not defined.

Old School Chopper Frame Fabrication - Knucklebuster

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