Suitcase Wheels for an "it" Suitecase

Awhile ago, when packing for a trip, I found that my suitcase had lost a wheel. This was a bit irritating, as it had been used exactly once, on a trip we took just before COVID struck. With the help of my Ender 5, I was able to make a new wheel from PETG. While it wasn't a long term solution, it held up well enough, and survived the trip intact. 

However, when I returned home, I found that another of the original wheels had separated itself from the suitcase. The issue is that this is a rather large suitcase, and the wheels are not strong enough to withstand the rough handling, given the heavy nature of the suitcase. 

Option #1 was to print another wheel like the first. I dismissed this approach, as riding along concrete pavement had worn quite a bit of the PETG away. This wasn't a solution that would last. Option #2 was to get a new suitcase, but it seemed to be a waste to buy another when this one had barely been used. It was just the wheels that needed better engineering. So I chose a third option as the solution. Print much more sturdy and well-designed wheels.

The suitcase has 4 casters, with 2 wheels on each caster. The wheels ride on a 6 mm axle shaft, swaged on at one end. There are no bearings, aside from plastic running on mild steel.

I'd much prefer that the wheels run on real ball bearings. I picked up some 606ZZ ball bearings and some M6x40 bolts with nylock nuts to replace the axles. The first part to design was a simple spacer, designed to keep each wheel spaced away from the central caster. I added a small flat on one end sized to match the inner race of the bearing, so the dust shield did not interfere with the spacer.

The next step was the wheel itself. I knew I needed the wheels to be able to take some abuse, so I was aiming to print them in ABS. I also wanted the bearing to be strongly seated in the wheel and have some mechanical fastening, so I didn't need to rely on a press fit alone. I decided to make the wheel in two halves, joining the halves using a M30x2 thread. The one half had the bearing press fit within it, and the other had a flange which mated up to the outer race, firmly holding the outer race on both sides as well as the OD.

I wasn't sure how printed threads would work, but after printing up a test piece, they proved to be a tight fit, and I don't think they will come loose in ordinary use. I did add a small hole to allow me to pin the halves together should that prove necessary. I'll definitely use this method on other designs in the future.

Another advantage of this design is that I could add a small flat on both sides, creating a bead to hold a real tire without resorting to a bunch of supports. I wanted to use a real tire of sorts, as hard plastic won't fare well on rough surfaces. I bought a roll of 95A TPU and printed up a test tire. The first version was a bit of a failure, as printing it with infill made for a tire that was too soft. I ultimately made the tire essentially solid, which is more approproate for the task at hand. I added mating undercuts to the tire to match the beads on the wheel. I also needed to make the ID of the tire about 0.5 mm undersized, to properly mate with the ABS, which shrinks as it cools.

After that, I set both printers to work making the parts. The Voron took on the ABS. I printed the ABS with 4 walls, 5 top and bottom layers, and 40% infill. The Ender 5 tacked the TPU. I ended up printing the tires one at a time, as I was struggling with stringing, and didn't feel like spending a ton of time tweaking settings. As long I didn't have to hop to another part every layer, I could avoid the issue.

I pressed the bearings into the parts as soon as the printer was done to try and take advantage of the ABS parts shrinking to create a tighter fit. 

As for the economics of this repair, I spent about $15 on parts and kept my suitcase out of the landfill. I'll conveniently ignore the $2,000 worth of 3D printers and countless hours of practice required to make this happen.

I took a trip using the wheels, and it was mostly successful. One wheel split apart, so I ultimately used a slurry of ABS and acetone to glue the threaded components together making a permanent, one piece wheel.

No baggage incidents have happened since this upgrade.