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I need to seal a rotating shaft that protrudes through a wall in a 3D-printed enclosure I am designing for a school project. The enclosure is for what will be a small generator that will be used in all weather conditions, so I'd like to make the shaft waterproof. To clarify, it is not the motor shaft that needs to be sealed, it's just a 1/4" diameter metal shaft which connects to some gears in the enclosure. Do I need anything more than a waterproof bearing (which I will be buying, not 3D printing) press fit in the enclosure wall? Such as, do I need some type of rotary seal as well? Is a press fit setting for the bearing enough to prevent water intrusion between the bearing's outer diameter and the enclosure wall? And how should I design the enclosure wall to hold the bearing (i.e. Is all I have to do make the wall the same thickness as the bearing? Does it need some sort of lip to hold the bearing?)?

I have searched for a long time online about how to do this, but nothing I've found is very helpful or is too confusing for me to understand. Any help is greatly appreciated!

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  • $\begingroup$ Is the 3D print waterproof? In my experience they mostly are not $\endgroup$ – joojaa Mar 7 '18 at 6:45
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    $\begingroup$ with the application of surface treatment, often epoxy, a 3D print can be made watertight. In itself, a 3D print is waterproof, as it is not damaged by exposure to water. $\endgroup$ – fred_dot_u Mar 7 '18 at 10:29
  • $\begingroup$ @fred_dot_u unless you're 3D-printing with chocolate :-) (don't laugh too much, as some chefs are playing w/ printers to create foodstuffs) $\endgroup$ – Carl Witthoft Mar 7 '18 at 16:28
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Being able to create a waterproof seal on a shaft would also have to take into consideration the water pressure on the outside of the assembly. In this case, waterproofing is more weatherproofing, reducing that aspect by a considerable amount.

I suggest that your waterproof bearing, unless otherwise specified, is not a water-sealing bearing. If the specifications reference resistance to water pressure, you may have a good solution, otherwise no.

In the boat world, one will find shaft drive systems in which the motor/engine is inside the hull and drives the propeller by a shaft which passes through the hull. The device which prevents the boat from sinking due to water ingress is called a stuffing box or a packing box. A search for those terms results in many hundreds of links.

The general design of a stuffing box is a series of seals restricting the flow and passage of water.

Consider that your shaft passes through a metal tube slightly larger in diameter and that tube is affixed in the wall of your 3D printed enclosure. One would choose an inside diameter for the tube to match that of a selected O-ring size.

The O-ring would be sized for a 1/4" inside diameter, and for example's sake, a 3/8" outside diameter. Your tubing would be also 3/8" inside diameter.

Carefully lubricate the O-rings with a silicone based grease and guide them over the shaft and press the shaft into the tube. Using at least two O-rings will provide for reasonably good protection from water ingress due to weather.

stuffing box

The above image is for a boat and is larger and more complex than you need for your project. The packing rings in the diagram represent the O-rings on your shaft.

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If your shaft only needs to be fluid-sealed during operation, consider the approach taken in the Wankel engine as produced by Mazda in their RX-series cars. They essentially reverse-threaded the shaft just inside the bulkhead point. Once the engine is running, fluid (engine oil in the Mazda case) is hurled away from the bulkhead by the threads -- more or less Archimedes' Spiral. They (Mazda, or anyone using this approach for an internal combustion engine) can get away with this because the oil level is well below the crankshaft when the engine is not running.

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