360 Scrape pads 3D printed

My 360 Spider had scrape pads under the front bumper when I purchased the car. They appeared to be pretty standard, made of HDPE or some other soft plastic, and had suffered some abuse over the years. I wanted to replace them but I didn't want to just buy new ones. Instead, I chose to manufacture my own using Fusion 360 and a Prusa MK3S+.

Digitizing an existing part can be tricky, even with a 3D scanner. If the item is relatively flat, a simple method of digitizing uses finely lined (1/10") graph paper and a camera. Line the object up on the graph paper so it starts at an even measurement, and the take a picture directly from above, at a fair distance away from the object to reduce spherical aberration. In this case, the old scrape pad fit easily on one sheet,

Fusion 360 has a very nice feature for importing images to use in their system. Once imported, a simple scaling operation gives the height and width. Tracing the outline and holes is quite easily

The original scrape pad, origin unknown.

I wanted this version to be more than a piece of plastic by being easier to "scrape off" and in the process, absorb some of the energy of the whack into an object. This design used pyramids set in rows so that the top of the pyramid is the easiest to remove, and as the scrape goes deeper, gets progressively more resistant to gouging. Hopefully, this type of design will reduce the shock of the impact.

Here's the design as it appears in Fusion 360. The pyramids are set at about 60 degrees.

Since the scrape pads are to be considered sacrificial, they need to be easy to change. The existing pad design called for lock nuts and a washer. To reach them, the bottom pan has to be removed. Very complicated. To solve this issue, I 3D printed "Nut Keepers" that would capture the nut and keep it from turning. The nut keeper has "wings" and holes to allow it to be affixed with epoxy. 

Here's the "Nut Keeper".

The screws being used are Everbilt #10-24 stainless countersunk oval head phillips with hex lock nuts. I bought them from Home Depot.

To mount the nut keepers, they were installed without any adhesive, with a #10 washer under the nut keeper. This provided a small space between the nut keeper and the fender inner surface so that the glue could be applied with a syringe around the nut keeper, into the holes and slots in the "wings". This proved to be quite easy and low mess. I used a total of twenty CC's of epoxy gel (Gelmagic of course) to secure them.

Here's the scrape pad installed.

Here's a link to the model files (.stl).

Scrape Pad Left STL Model

Scape Pad Nut Keepers STL Model