Food Storage Jar Seals

Three decades ago, we bought some glass food storage jars, and really enjoyed them. For the last decade or so, though, they’ve sat in the corner of the kitchen as little more than a decoration because the seals have dried up, cracked and allowed the food to spoil. We recently decided to 3D print some new seals for these.

The first step was to remove the old seals. After plucking off some of the worst portions of the seals, a good amount still remained stuck to the glass, as shown below:

Our first effort to remove this old rubber seal was a disaster. Using a small screwdriver, we tried prying up on the rubber, and managed to bruise the glass. If we had been interested in flint-napping glass, as described in the second chapter of Caveman Chemistry, this would have been great. As it is, the internal cracks rendered the first lid unusable for food. Since we had one jar with existing damage to the lip, we’ve paired these for storing things such as seeds for planting (plus a desiccant pouch to absorb moisture).

The next thing we tried is softening the old rubber first with an orange-based solvent, and let it sit overnight. We used Goo Gone, but many other orange-based options would probably work as well. Rather than using the screwdriver tip to pry, we scraped at the softened rubber as if we were using a tiny glass scraper blade. The first effort removed almost all the rubber. After a second overnight soaking in solvent, the remaining scraps came off completely and easily. The jars and lids then went in the dishwasher for a final cleaning.

Next, we designed a seal in FreeCAD, and used our Taz4 FlexyDually to 3D print a new seal using silver NinjaFlex. Our first effort was a simple flat disc, but this allowed the lid to rub, glass-to-glass, on the jar lip. This is a bad thing. Plus, our first seal was too thick, keeping the wire closure from working properly. Next, we reduced the thickness, and added a small lip to the inner edge, which worked better, but still wasn’t good enough. We then changed to an angled lip, as shown below:

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This cross-section is then rotated in space to create the final seal. Note the slight angle on the lip, which works great with the additive process. The first angled lip was too small. The fourth try was what you see above, and is available as an STL file. The final seal is shown below:


Next, we washed the seal, and then installed it on the lid, as shown in the picture below.

The inner diameter of the seal is a little less than the inner glass edge, so the seal is stretched a little bit to get it in place. A side view of the tight seal, and how the lip protects the glass edge once the seal reaches its final orientation, is shown below:


Here we show the lid on the jar:


And a top view:


With this final seal design, there is no scraping of glass-on-glass, and the lid fits snugly on the jar with no stress required to close it. Other than the wire closure showing three decades of age after a trip through the dishwasher, these jars are now as good as new, and catching a second life storing staples.

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