Puffin - work in progress

[Subculture]

Would it not be better to make any parts that are subject to torque and shear from something a bit tougher like solid plastic or composite sheet. Or use something like SLS or MJF printed nylon?

[Occupant]

Started with ABS-GF print first with printed TPU seal - leaked, commercial o-ring - leaked. so thought it was the print leaking? Came across CPSdrone on Youtube. they used Dichtol to seal printed parts. contacted the company and at the time they didn't sell to the general public and it was pricey. Pivoted to a resin print - ABS like resin. tightening down on the gasket cracked the flange off the part. it hadn't dawned on me that the increased strength comes with increased brittleness - like a piece of glass. Frustrated thought about the Dichtol again and on a whim searched it on Amazon - what, its available??? still kinda pricey but works.
Another idea would be to use a washer plate and nut plate (both shaped like the gasket) sandwiching the two WTC halves against the gasket and spreading out the load vs point load at each screw, wish i would have thought of that earlier.

So to further troubleshoot the two possible leak paths are the ballast inlet tube and the gasket seal. For the ballast inlet connect to the ballast syringe vs plug hose end. As for the gasket two things to do here measure the gap around the gasket to try and ensure a uniform squeeze on the gasket. if that still seems to be the issue may have to sand and reseal the surfaces that interface the gasket (hoping the gasket is soft enough to conform and seal) it could be enough of a peak or vallet that could create a leak path past the gasket. .


FYI
Nylon is a highly hygroscopic material that absorbs water (up to 8%+ at saturation), causing significant changes in its properties. While it remains durable and, in textile form, quick-drying, water absorption leads to increased flexibility, toughness, and part size, but reduced strength and stiffness. It is not recommended for high-precision, submerged applications without consideration for dimensional shifts.

[Subculture]

I wouldn’t worry about hygroscopic properties of Nylon for a part like that in a model sub. For one they're not submerged for very long, and secondly the tolerances are fairly modest. Something dunked in the drink 24/7 is another matter, although these materials have been successfully used for the latter without any ill effects.

I’m sure a plate to distribute the bending load will help a lot.

[RCSubGuy]

Also recall that ABS parts can be vapor smoothed
with acetone, creating a perfectly sealed surface. I, personally, have not had an issue with leaking filament parts. Leaks are usually caused by part interfaces, not the parts themselves.

[Occupant]

For what its worth tried the acetone smoothing with less than stellar results. Have moved past it, think its hard to get repeatable reliable results. Do you do any ironing on your filament parts or just leave all the settings as default?


Back to trial and error, error, error..... in trouble shooting mode again. a bit of history to where i'm currently at, looking for any help you want to offer..
the Water tight container consists of a nose piece printed in translucent ABS, sealed with Dichtol AM Hydro. it has three penetrations - 2 fin servo connectors and one hose fitting for ballast line. the servo connectors are gap filled super glued in place and then potted in with casting resin. The Ballast line brass fitting is secured/sealed using JB weld. it was tested by filling with water like a cup facing up, 24 hours later no water had leaked out. the tail section is a Black ABS again sealed using the Dichtol sealant. the tail sectiononly has two penetrations motor wiring and rudder servo. they are held in place with gap filled super glue an then potted in with casting resin. this was tested cup up configuration like the nose with water for 24 hours - no leak.

yesterday took the halves assembled with silicone gasket between weighted to the bottom of the pool, 15 hours later pulled and opened - damn a bit of water...somethings leaking.





Dried it out, reassembled and weighted such that the silicone seal and motor and rudder wiring are submerged taking the ballast line and fin servo connectors out of the equation to see whats leaking.

While i was at it decided to take a rough look at trim weights to level this out by installing the front half of the body and putting dive weights in it... quick and easy trim weight approximation. In the process noted something that may solve the leak issue - the canopy is JB welded to the cockpit base ( both pieces are resin prints) and has come loose? Does JB weld not hold up in water? Used JB weld vs potting resin on the ballast line. FYI tried googling and kept pointing back to B waterweld - I used regular JB Weld

[TuptubBuilder]

I have had success with closed cell neoprene sheet as a gasket material. You can get it on Amazon in 1/16 or 1/8 thickness. Print the gasket file in PLA and use it as a template.

[Subculture]

Slow cure JB weld should be waterproof but I would leave it for a few days to fully harden before putting it in water.