Ever since 3d printers became a reality people have tried to print wheels.
Skateboard wheels are a logical first step, they are small, easily modelled, bearings for them are cheap and just about everyone has access to a skateboard.
Most people start with solid ABS or PLA wheels, there's is even a very detailed 'ible about printing them in photopolymers: https://www.instructables.com/id/3D-Printed-Skateb...
Unfortunately, these don't work very wheel, PLA and ABS wear very quickly with the outer walls of the prints breaking away from the rest, leaving a trail of plastic fibre behind you as you roll. You can see this in image 2 which I pulled from this video on 3d printing skateboard wheels: https://www.youtube.com/watch?v=hZl3tD0yl4A
Recently I've been experimenting with TPU which is a rubberised 3d printer filament and I was quite surprised by its strength and layer adhesion. I've printed a few combat robot chassis in it and it survives the biggest and badest weapons in my local competition. Because TPU is rubberised it's not a great material to provide support, so I decided to try it as a tire for a wheel and it held up quite well!
You can see my build here:
Or follow this instructable to build your own!
Step 1: What You Need
This is quite the short list:
A 3d printer
TPU and PLA filament
a screwdriver (optional)
and some design software.
The trick here is to have a printer that can print TPU because it is a rubber-like filament it can be difficult to print. We'll talk about setting your printer up in a later step, but for now, it's best to have a direct drive extruder on your printer. A Bowden extruder may make this a lot harder
Step 2: Design
The design of these wheels is key to their success, 3d printed parts can be weak so we want to leverage some geometry to add strength to the parts before we even start printing.
This design is nice and simple its basically 3 cylinders with some small modifications:
- The first cylinder is the outside diameter of your wheel this can be anything you want it to be.
- The second cylinder is the outside diameter of the wheel hub, I recommend a radius 5mm smaller than the first cylinder for a large wheel and 3-2mm smaller than the first cylinder for a small wheel
- The third cylinder is the skateboard bearings, these have a radius of 11mm
To get started, make a copy of the second cylinder and use it to core out the first cylinder, this should create a nice ring tire.
Extrude the middle third of the tire inwards by a maximum of 3mm. extruding in any more will make the tire very difficult to get on. Champher both edges of this new internal ring so that it prints easier (the tire ring should now look like the item to the left in the image).
Make a copy of the tire ring, centre it on the second cylinder/wheel hub and subtract it, this will leave a ridge in the wheel hub for the tire to lock into
Now its time to add strength to the wheel hub with some geometry, we need to design in spokes that will increase the surface area of the print and compliment the print settings we will make in the next step.
The easiest way to do this is to subtract arc/triangles out of the hub. Simply create an arc or a triangle, position it between the centre of the hub and the outside, create 4-6 copies around the centre of the hub and subtract them.
Finally, add space for the skateboard bearings, increase the radius of the bearing cylinder to 11.1mm-11.2mm to allow for printing tolerances and subtract the bearing cylinder from the top and bottom of the hub, leaving a disc 9mm thick between the top and bottom subtraction.
Download my files
Step 3: Printing Strong PLA Parts
The hubs of these wheels need to be strong!
So some tweaks are needed to your 3d printer settings.
As a general rule increasing infill will increase the strength a little, increasing the wall thickness and top/bottom layers will increase the strength more. Heres a helpful video:
So for our purposes, we want to keep our infill at a modest 20% and increase the wall thickness to 5-7 walls with the top and bottom layers similar
Step 4: Printing TPU on a Stock 3d Printer
TPU is difficult to print because it is a rubberised filament it can bend and flex as it feeds into the hot end and it will always try to take the path of least resistance. This means that any back pressure that builds up in the printers hot end will force the TPU to bend and jump out the sides of the extruder gear.
To avoid this back pressure, some slicer settings need to be changed, the print bed needs to be releveled and coated.
Print speed: <10mm/s (this needs to be slow to ensure the TPU feeds correctly)(this will cause looong print times but its worth it)
Raft: on, Air gap 0.3mm, initial Z overlap 0.15 (this will help hold the print down to avoid warping)
Cooling fan: off (TPU prints hot, so a cooling fan will cause your parts to warp)
Supports: Off (TPU sticks to its self very well, so supports would need to be removed with a knife, this is not recommended, so try to design parts that can print well without supports)
This is the big trick I found to printing TPU, your bed needs to be levelled further away from the nozzle then normal. Leveling the bed one paper thickness away from the nozzle as normal makes creates a large back pressure in the nozzle forcing the TPU out of the drive path and stopping the print
Instead level the bed 2-4 paper thicknesses away from the nozzle (images 2 and 3)
Apply a liberal coating of glue stick to the bed. the settings and bed level we have to use to get the TPU to print are not ideal for getting the TPU to stick to the bed, however, TPU sticks well to glue stick allowing the print to stay stuck to the bed.
Step 5: Assembly
The two halves of the wheel have been designed to be a tight fit so they don't come loose while riding.
That makes this step a little bit more difficult.
The easiest way I found to get them together was to place the TPU tire on the ground, sit the hub into it and stomp on the hub. A well-placed stomp should get the tire halfway on, it can then be levered on with a flat head screwdriver or by hand.
Apply skateboard bearings to either side and attach to the skateboard just like any other wheel.
Step 6: Results
Working skateboard wheels!!!!
I've run my wheels for over an hour so far and besides some discolouration, there is very minor damage and no evidence of the outer walls starting to peel away.
This is a great way to create custom sized Skateboard wheels and have the coolest maker-board around.
The whole project could be done faster using an extruder designed to print flexible materials (such as the flexion extruder) allowing for greater freedom in design and a nearly infinite supply of wheels