Car Guy Bartering

I designed a 3D printed a part for a friend who's working on a skunk works project. If I told you what it's for, I'd have to kill you. He's probably answered a thousand of my questions, so I got the better end of the deal! It's designed to attach to the hexagonal rod on a linear actuator.

I printed it in Onyx which is composed of tough nylon and chopped carbon fiber. Since the part will see a fair amount of stress, I reinforced it with continuous strands of carbon fiber. The slicer provides two layout algorithms:

  • isometric: follow the outer edge a specified number of times (i.e., rings)
  • isotropic: diagonal fill

The choice between the two comes down to how you want to orient the strands for strength and how much continuous fiber (e.g., fiberglass, HT/HS fiberglass, Kevlar or carbon fiber) you want to use. Isometric allows you to control how much continuous fiber is used by specifying the number of rings whereas isotropic fills the entire layer. The proprietary carbon fiber is expensive, so you want to be conscious of how much you use.

For this part I used isometric layout to provide strength where it's needed and to reduce the amount of continuous fiber. In a previous post I had pointed out that their isometric fiber routing algorithm didn't wrap interior holes unless there were enough rings to intersect the hole. For example, in the image below three are three rings around the perimeter, but none around the hole. Even then the rings intersect the hole, they weren't optimized to reinforce the hole.

I was concerned about this shortcoming because the all of the stress will be transmitted through three interior holes -- yes, they have press-fitted metal bushings, but that's where we want the most reinforcement.

When I went to print the part I was thrilled to discover a new "Walls to Reinforce" setting with the following choices: All Walls, Outer Shell Only, Inner Holes Only. One of the advantages to having a cloud-based slicer is that upgrades are automatic. In any event, for this print I selected All Walls and two rings. This wrapped the outer shell and the three inner holes with two rings of continuous carbon fiber. Note how thick the outer shell and inner hole walls are. Also note the hex recess. The material inside the notch on the left (i.e., the hex recess) is to support the horizontal ceiling of the hex which hasn't been printed yet. If you look carefully you will note that this support material doesn't span the entire opening because the faces of the hex that support the ceiling don't need support material. In other words, Onyx can be printed with a 60-degree overhang.

While we haven't done any destructive testing yet, the part feels very robust and nothing like nylon.