Custom Fixturing

In last month’s column I showed how I put a 1″ diameter axle in the rear wheel of a Harley motorcycle that originally came with a ¾” diameter axle. That was done because the bike had a big increase in horsepower and the ¾” diameter part got bent. That in turn required a custom rear brake caliper bracket and custom fixturing to make the new bracket. Figure 1 shows the new caliper bracket. Note that there are two holes through the part. The smaller hole is 1″ diameter and mounts on the axle. The original equipment part didn’t have enough material to accommodate this hole safely. The larger hole is the same size and location of the original equipment bracket. There are also two 3/8-16 threaded holes for mounting the caliper. I put two studs into these holes and use that assembly to index a piece of wrought aluminum for machining. Figure 2 shows the fixture I used. Figures 3 and 4 show the work in process. The fixture plate is made from 1¼” x 5″ 6061-T6 aluminum bar stock. I like this material for making fixtures because it machines quickly and doesn’t rust. I am in Massachusetts where it gets very humid in the summer and rust can be a nuisance.

Figure 1

Figure 2

Figure 3

Figure 4

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