(Un)rolling Along: 3D Printed Seat Bag and Fender

This started out as a serious project to design a combination seat bag and fender, but somewhere along the design process I decided to make it look like a roll of toilet paper blowing in the wind...

Step 1: Materials

I chose 3D printing for the initial prototype and maximized the size for my printer (Craftbot +).

This version was printed as a single assembly and at 0.3mm layer resolution it still took 11 hours to print.

I mounted it to the seat with cable ties, but for a more secure fit I would make a top plate and use screws.

I used PLA filament for ease of printing, but PLA does not bend much before breaking. For a more durable part I would consider ABS, PETG, or even Nylon filament.

NOTE: I have attached individual files at the end to allow the "paper tube" to be printed in a different color and to create the seat bag storage feature.

Step 2: Use "Sweep" Feature to Create Waves

There are already many good Instructables on Fusion 360, so I will only focus on the main features of this design.

To create the waves, I started by Sketching a simple sawtooth pattern.
Use Sketch, Fillet to round out the corners.
Drag the endpoints of the lines and adjust the size of the radii to achieve the desired wave profile.
Stop Sketch.
Sketch the cross-section of the paper perpendicular to the wave and Stop Sketch.
Use Create, Sweep to create the wave.

Note: At this point I could have specified a Sweep "Twist Angle" to twist the end of the paper, but at the time I wasn't sure how I wanted to show the end of the paper fluttering in the wind.

Step 3: Use "Loft" Feature to Create Tail Section

Construct, Offset Plane to define the length of the tail. In my case this was defined by the size of my printer.
Sketch the end profile of the tail. I chose a simple twist, but could have added a ripple, etc.
Stop Sketch.
Sketch, Project/Include, Project and select the end profile of the wave.
Stop Sketch.
Create, Loft to create a tail with a slight twist to it.

Step 4: Use Planes and "Mirror" Feature to Center Hole Pattern

Construct, Plane at an Angle to define a plane for the mounting holes.
Construct, Offset Plane to define a plane beyond the part (i.e., looking down at the part).
Sketch mounting holes. I could have drawn all 4 holes at one time, but chose to mirror them so that the hole pattern remains centered on the part (Note: You can also mirror the holes in the sketch and skip step 5 - personal preference).
Extrude, Cut the holes, either a fixed distance, or in my case, I chose the inner cylinder to stop.
Create, Mirror the holes about the middle plane of the part (Note: If the original cylinder was extruded in one direction instead of symmetric, you'll need to construct a middle plane).