Nylon Filament

The bottle cap I'm working on obviously needs to not leak, by sealing to the top of the bottle. It has two problems: it's made of PLA which is rigid, and the underside of the "deck" is irregular because it is printed over a grid of support material. Most bottle caps use a soft plastic gasket or washer where they meet the bottle, maybe nylon or teflon. I figured it is unlikely I would find a suitable part of exactly the right size, so naturally I thought about printing it, and looked into nylon.

Nylon has become available for 3D printing in recent years. From what I read it is rather more difficult to work with and about 50% more expensive than PLA. I need only a tiny part and didn't want to buy a whole spool just for that. But I think I'll find other uses for it, so I ordered a 1-pound spool. A filament called Bridge from Taulman seems to be rather popular because it reduces some of the problems with earlier products.

It occurred to me that maybe I could print the whole bottle cap in nylon and avoid the need to fit a gasket. Rather than print the whole thing, I first printed a "slice", the center section of the bottom, so I could observe the threads. I needed to adjust the depth of the bottom anyway. (I like finding shortcuts to avoid printing the whole part every time.)

With nylon one can't use hairspray for adhesion. The two popular methods are glue stick and blue tape. I tried the glue first. It's easy to apply. My first print stuck well except for one arm. It seems I didn't get the glue over the whole print area, which seemed strange. I tried again and missed again. What's going on?

My printer has a glass heated bed. It has a rectangular "hot zone" printed in it, and the Robo3D logo in the center. Except... it's not centered! All this time I've been applying hairspray roughly on the logo and it's been working OK but only by luck. Reading on line confirmed this. I had noticed that the nine leveling touches didn't line up with the square but had not thought it important. Kind of dumb of the manufacturer to print something that implies alignment and not line it up. So I measured things and made a center mark, applied glue accordingly, and it stuck fine.

After making some minor adjustments I decided to try printing the whole bottom half in nylon. It printed OK, but two problems arose:

• The support material was really hard to get out. It took a lot of cutting with a Dremel saw bit and a lot of pulling.
• The bottom is too flexible. When I close it tight the threads can actually skip and lose the seal.

So I won't be producing the whole thing in nylon. Now I'm working on designing a gasket that will be held in by friction and act as a seal between the bottom of the deck and the glass bottle neck. The whole bottom needs some size adjustment, and since the gasket is also parametric it will resize at the same time.

The other method for adhesion is blue painter's tape (masking tape). It's thicker than glue, so now I'm trying to figure out how to adjust the Z dimension upward. MatterControl shows a Z offset but does not let me change it. If I don't move it up, the nozzle drags a groove in the tape and does not extrude properly. I'm not sure how to only place tape in the center and still have the auto leveling feature work. If there's no tape in the  other eight spots, the algorithm will not adjust the Z. Do people tape the whole bed? That seems excessive. Maybe I need to add tape in all eight leveling spots.