Filter for re-using rinse alcohol from 3D resin printing using $5 pool filter cartridge [OpenSCAD]

A common, effective, and cheap method of cleaning alcohol (IPA or denatured) used to rinse 3D resin prints is to leave it outside in a glass container for a while (here in Arizona, about a week) so the sun can polymerize all the resin dissolved in the alcohol, making it non-toxic. The polymerized resin settles to the bottom as small particles, but it need to be filtered out before the alcohol can be reused.

This filter holder is part of the system we use to do this, shown below:

The system comprises a 2 gallon glass jar (Anchor Hocking, $14 at Wal-Mart) a pool filter cartridge (INTEX #29002E, for type A or C cartridge pool filters, 2 for $10 at Lowes), and a wide-mouthed plastic jar (this one was a cat treat jar, but peanut-butter filled pretzels come in this size, or you can use a 64 oz. peanut butter jar.)

There are a couple of ring depressions printed on the bottom of the holder around the central hole. These serve as “drip edges” to make sure the alcohol doesn't flow outward along the bottom of the filter holder. They worked very well. Also, the interior floor outside the filter is elevated and sloped to minimize fluid accumulation outside the filter.

I used a stainless steel ladle to transfer most of the IPA from the glass jar to the (outer area of the) filter holder during my first test run, to not disturb the sediment on the bottom of the jar. Once I was at the limit of what the ladle could do, I poured the rest of the alcohol on the jar into the holder, but stopped pouring when the sludge would have poured out. The limit on how fast I could process alcohol was the rate at which I could ladle it: the pool filter cartridge is fast, unlike coffee filters, and still blocks the sediment. After all, this is what pool filter cartridges are designed to do.

Once the cat treat jar was filled, I poured the filtered alcohol into the jug it came in using a funnel, then repeated the process.

Doing that, I recovered over 75% of the IPA, which was slightly tinted but otherwise clear, and suitable for reuse washing resin prints. (This was a much better yield (and with far less work) than I had previously achieved with distillation, where I only recovered 40%.)

I then scraped the sediment out onto a few spread-out junk mail flyers and let it dry in the sun. A few hours later it was ready to throw in the trash. Since it was thoroughly polymerized, it was safe to throw it out. Then I cleaned the glass jar with soap and water.

[For those looking closely, yes, there is a gasket on the glass jar that didn't come with the jar. I printed it from TPU. The model is here as “seal_for_2gal jar” both as STL and OpenSCAD.]

Installing the filter is easy, just press it in to the filter holder, it will fit in the cavity for it. Don'[t push it too hard, though: when you start getting ripples in the pleats like this:

then get a flat-tip screwdriver or other tool, slip it between the pleats, and push down on the rubber end of the filter:

I actually like do this all around the filter to ensure a good seal.

I am very happy with how this works. It look like I can do maybe 8-10 2-gallon batches with one filter cartridge (4-5 on one end, then flip it upside down and use the other end) which means I'm only spending $0.35 per recovered gallon, a nice savings.