Bolt-on steps - Part 3 - assemble upper channel and step support bracket

The 3.2mm holes of the step support brackets RF-BKT-019-L/R-A- were all upsized to 4.1mm for stronger 4mm rivets. Despite - particularly on the upper attachment - the limited hole-centre to edge distance varying from 7mm at the front to just 6mm (i.e. 1.5D) at the rear it is felt the use of larger rivets will reduce the likelyhood of fretting of the rivet shaft by spreading loads over a greater area. On loading and unloading the step, it is expected these attachments will be subjected to substantial cyclic and twisting forces.

The rivetting of the upper attchments had to be carefully sequenced as a conflict existed between the rivet tail and nutplate prior to setting. The rivet needed to be lightly tapped down into postion to force it past the nutplate tail. On setting this situation corrected itself and the shortened fully set tail created no conflict with the nutplate nor the AN3 bolt tail.

As with the lower step attachment, the final chuck reaming to 3/16" was done with all layers in place, including the custom nutplate block, upper step mount and custom doubler, the latter of which was used as the reaming reference.