Custom longeron 301 upsized hole strip washer

The holes in longeron 301 along the full extent of the rear top skin have been upsized from 3.3mm to 4.9mm. The 4.8mm rivets now used will be clamping a 0.4mm thick rear top skin, alternatively a 0.63mm rear bottom skin or 0.51mm side skin, and the 0.8mm longeron 301. This is a total thickness of 1.7-1.8mm. I found that riveting such a small total thickness with a 4.8mm rivet a small amount of dishing was visible in the sheets, due to this slightly concave undersurface of the rivet. It also did not help that the layer of sheet directly under the rivet head is the thinnest at 0.4mm. In effect the sheets were deforming slightly ahead of the rivet head forming flat. In order to prevent this effect I found an additional 1mm sheet against the tail of the rivet provided enough rigidity to prevent the dishing of the layer underneath the rivet head. In effect the rivet head was formed flat against the now 2.7-2.8mm total sheet thickness.

Based on this I decided to back up the longeron 301 with a strip "washer" made from 1mm 6061-T6.