u/Im_No_Cartographer

I have a sheet metal part I need to attach to a 4mm motor shaft (which has a flat on it). For a one-off design, I'd just tack-weld the sheet to a stub shaft and use a coupling to connect it to the motor but off the shelf coupling are expensive, and I'm targeting production volumes in the thousands, so I need to drive cost down as much as possible.

My proposed approach:

Bend a hem into the sheet metal part such that the hem's centerline aligns with the centerline of the sheet's thickness. This would create a circular boss of sorts, centered on the part. I'd then secure it to the motor shaft using a grub screw bearing against the flat. At the opposite end of the shaft, I'd insert a 4mm round rod and again fix it with a grub screw.

Application context:

• Rotation speed: 1 RPM
• Max torque: 0.5 Nm
• No balancing or high precision required

My questions:

1. Is this hem-based hub approach actually manufacturable at scale, and are there any gotchas I should be aware of?
2. Is there a better / more common way to couple sheet metal parts to small shafts in low-cost, high-volume applications?

I'm looking for a fitting the I would call a "Sheet Metal Plug" but that may not be the correct name. The fitting is similar to the one pictured. It would be made with a rubber and the larger section could be pushed into a hold in sheet metal. The smaller section fits into the hole in the larger section to create a seal and there is a tether to keep it from getting lost. The purpose of the fitting is to provide a port in HCAC equipment where static pressure can be measured. Does anyone know where to find these or a name that might help me find them?