I am in the process of designing a compressed air powered model car to 3D print in carbon fiber and other materials. My question, and main concern, is if the motor and drive train parts can be printed so that the assembly is air tight when printed with carbon fiber. I will use some kind of sealant if I have to. But if you guys don’t think carbon fiber will work, what other light weight material would work?
MB3D
2
a) why does the desired part need to be air tight? b) Carbon fibre basically means carbon fibre reinforced plastic so the weight does barely differ from 100% plastic parts Some materials that could work are XT, ABS or XT CF20 Please share some more detailed informations and maybe even the 3d models to get proper quotes and material recommendations. Cheers, Marius Breuer
The reason the drive train, mainly the motor parts, need to be air tight is because compressed air will be flowing through the motor to power the wheels. If air is leaking out of the front or any other part, the motor will loose power.
So it sounds like a light weight material is out of the question, but carbon fiber reinforced plastic should be much stronger. And strength is important so I can supply more air pressure, as in more power, to the motor.
I don’t have much of the motor designed yet, so I currently have no image or model to share. But the motor is based of the exhaust side of a turbo charger and will work the same way. That is why the material/assembly needs to be air tight.
In order for it to be air tight the tolerances will have to be very precise, more precise than can be obtained with filament 3D printing alone.
Without seeing designs its hard to comment on airworthiness or likely failure areas, but it doesn’t sound like something particularly suited to FDM printing,
Just my coin in the bucket on this: you should go for ABS, structurally check your model with tools like Solidworks (if you have access to it) for air pressure. What is the pressure you’re looking at? 125 psi or more/less? Get it printed using FDM technique and use acetone vapor smoothing to strengthen the part.
Else FDM is not really suited for this, and generally parts will never be water tight, let alone, air tight.
Overall… sounds like a challenge 
I have printed air tight parts using XT and ABS and it works just fine.
for example I’ve printed vacuum mounts and cooling nozzles.
as long as your not printing an air tank that goes under a ton of pressure you should be able to design and print air tight prototypes that do the job.
for moving parts use rubber seals like you would do on any part that requires such a seal and use the printing capabilities to your advantage to design complex geometries that help close the seal.
It’s also possible to print treads in the Z direction that screw airtight.
for shells that lock together use some cord gasket and cleverly placed machine screws to lock them together.
good luck
and remember 3d printing is an art, art is failure, try again fail better. 
On the front of the motor I am planning on installing a cap with a bearing to hold the drive shaft and will be held in place with screws. I didn’t it was possible to create air tight threads, that would work great to connect the back end of the motor to the exhaust. I’m not planning on having an air tank 3D printed, I’ll use a metal pipe with the ends welded to supply higher air pressure to the motor.
I am new to 3D printing so I don’t know much about the materials, but I would think carbon fiber would be the best choice for the motor due to it’s strength. I don’t think I’ll use 125psi, most likely closer to 100psi.
carbon-filled might be overkill and it’s a tricky filament to start printing with due too it’s high abrasiveness to the printers nozzle.
that’s more suited for long thin light drone arms etc.
regular XT, ABS or nylon would be some good options to start with.
In reading the descriptions of XT and nylon, they both have some flex to them. The rotor needs to be stiff. I’ve had one item printed with ABS and it does seem stiff enough. But ABS prints rough and is hard to work with if any part needs to be filed down. From the little I’ve seen, it looks like carbon fiber prints smoother. But if you really think ABS is the best for the rotor, I’ll go with your experience.
It all depends on your design and printer.
If the printer is setup, calibrated and you have the right settings you can get smooth prints with most of the filaments.
any plastic will have a tiny bit of flex in it however a solid design won’t flex as much as a flimsy design.
XT, nylon, ABS and PLA all will be pretty stiff when you construct a solid model.
