I got an XTool Smoke Purifier recently, but it was quite dirty.
After opening it, you can remove the filter stack from inside. Within the filter stack, you'll find a mesh-type pre-filter (kind of like thick wool), then what appears to be 2" HEPA filter, and then probably some kind of other filter with activated carbon below.
I took out the pre-filter and washed it out, and then dried it. It was absolutely filthy. I've seen a YouTube page that suggests getting aquarium filter mesh for that, and I might yet do that.
After I put the cleaned (somewhat clean) pre-filter, I put it back in, and tried running the extractor. But I found that there wasn't any air coming out the exhaust. I tried doing the same without the HEPA filter portion, and got good air flow, so that meant the HEPA filter part was gunked up beyond repair, and had to be replaced.
The overall stack can run about $100, bought new. I didn't yet want to spend that kind of money, so I searched around quite a bit, and finally found a filter that was close in size, but much cheaper. The original filter was around 14" long, 6.5" wide, 2" deep.
The replacement filter I chose was a KJ190. It cost $12.99 and comes with spare pre-filter layers.
The KJ190 is about 13.4" x 10.6" x 1.33". I couldn't find anything similar and cheap for the 2" depth.
After a bit of deconstruction, I found filter part is more like 13-3/16" long (est 335mm), not 13.4". I'm pretty sure they state 13.4" because that includes the size of a thin insulation strip.
The overall construction is like this:
The inbound layer is a thin mesh of some sort as a pre-filter. It's held to the main frame by Velcro strips that are glued the main frame's surface.
The frame itself has a kind of cardboard frame. Inside it, you have the HEPA paper-type pleat.
Beneath the HEPA part, there's a plastic honeycomb that is sandwiched between nylon-type mesh. Each honeycomb cell holds activate carbon bits (typically 3 to 5 little pegs per cell). The mesh is glued to the honeycomb to keep the carbon bits from wandering.
For my purposes, I wanted to cut the filter down from 10.6" to 6.5" width.
In order to do that, the first step was to cut through the outermost nylon mesh, and peel it back. I measured the size roughly by putting the old filter atop the new one, and making marks. Removing some of the nylon, allowed me to empty out most of the activated carbon pegs. I say "most", because there were still honeycomb cells under the paper frame that I couldn't get to.
I used a box cutter to cut through the paper frame at the mark points. On each surface, I cut at a 45 degree angle in anticipation of rebuilding that edge. Then, I peeled back the side frame, and removed any remaining carbon bits.
Next, I did a test cut of the filter, using my bandsaw. Then, satisfied with how the test went, I cut through the filter from end to end, again using the bandsaw. That cut could be done pretty easily manually without any kind of sled or guide.
This is the part that was cut off with the carbon pellets removed.
With that done, I tore apart the portion that I wasn't using, and pulled off the Velcro strip.
At this point, I did a test fit, putting it back into the original filter stack.
Next, I modeled a piece of for the side so that I could replace the frame edge. It started as a rectangle, 32mm (filter thickness) x 335mm length. Then, I added 12.6mm-wide strips to the top and bottom, but cut them off at a 45 degree angle (so the top and bottom each have a trapezoid added).
I exported that as .svg, and then added a "score" box. When doing the laser cut, I run the score line first, followed by the cut.
I had an old piece of black posterboard from the Dollar Tree, so I cut a chunk of that so it'd fit in the FSL Hobby Laser (CO2).
For engraving, I used 90% speed, 5% power. For cutting, I used 80% speed, 15% power. In both cases, I had the current meter turned 4 full revolutions. That cut all the way through most of the time. At 20% power, it cuts through cleanly, for sure, but there's more significant flaming. I forgot to turn on air assist, but it cut through well.
This picture shows two cuts that made it through, and one that had the cut power too low.
Scoring close-up
I pre-folded the piece along the score lines, ending up putting the score lines on the inside for aesthetic reasons.
I tried different ways of gluing it, but in the end I think I could have done better this way:
1. Remove the current pre-filter so that it's not in the way. (In my initial run on this, I only peeled it back, and then used a binder clip to keep it peeled out of the way while gluing.)
2. Cut off a small portion of the Velcro on each side -- enough so that the salvaged long Velcro strip could be glued over the corner later, without running into the side Velcro.
3. Tape the end of the laser-cut strip on one side in order to maintain alignment
4. Hot-glue the middle section (the long rectangle) of the strip to the filter paper
5. Tape down the not-yet-taped end of the strip to prevent movement.
6. Bend each folded portion of the strip outward, apply hot glue, and then bring it down to the honeycomb. On each side, the layering is strip, hot glue, nylon, honeycomb.
7. Glue the long strip of honeycomb back on to the long end. It should run from end to end, going over the 45-degree cut lines.
8. Apply dryer duct tape (the thin, silvery kind) where necessary to tighten things up.
With all that done, I had a pretty good replacement filter, except that
1. It's not as tall/thick as the original. That's ok. I can run with a thin one for now, or add another one later.
2. It's not long enough. Mine is 13-3/16" long, but the original was more like 14".
To fix the gaps in the length, I had some spare 3/8"-thick, adhesive insulation strips that I got for free at a garage sale. I cut three sections to the needed filter width. I added two on one end, and one on the other, and ended up with a decent fit.
Finished replacement, installed in stack
All said and done, I turned on the fan, and got good airflow. Now, whether or not that's really "good" remains a question. In the end, I was able to fit the KJ190 filter into the original stack quite well, but it's running with a much thinner HEPA layer than the original. Still, I was able to do this at about 1/8th the price of a whole new stack, and I ended up getting a few spare pre-filter layers.
Next steps
1. Perhaps get a second one and double-stack it
2. Do some test cutting to see how effective it really is at clearing smoke. Plus, see how dirty it gets over time.
3. Consider replacing the original "wool" pre-filter layer with the aquarium filter material described in YouTube.
Another option
Well, after doing what I did to the KJ190, I felt like it freed me up to tear apart the filter that normally comes inside the original filter stack, and see what makes it tick.
As it turns out, it's a much simpler thing. Many filters you buy these days, the KJ190 included, have a "2-in-1" or "3-in-1" marketing tag. The KJ190 is a 3-in-1, in that it has a pre-filter, the HEPA area, and the carbon pellets. The trade-off is that you end up with a thinner HEPA pleat. I think mine is probably only about 0.5" thick.
When I tore apart the original, I found that it's just a box containing a much thicker HEPA pleat -- probably somewhere a little under 2" -- and two metal grates to keep it in place on both sides.
As such, I think I could use an F1 filter. That one is touted to be 6.7" or 6.75" wide, 12 inches long, and 1.7" thick. It appears to be a plain old paper frame with a HEPA pleat inside. That's much closer to the original. I think one of those could be plopped right into the filter stack, and then I'd need 2" (1" on each end) of padding to fill out to the original 14" dimensions, and then maybe some thin insulation strip around the edges in case there's a gap between the 6.7" F1 box and the original.
The only catch is that in some cases, if you try to order the wrong one, it will say that it cannot be shipped to California because of some clean air law. But, if you click around a few times, you still might find one (or a pack of them) that doesn't trigger that limitation in Amazon.
The F1 filter
I ordered a set of F1 filters, and they're pretty darned close and should be a lot easier to use than the KJ190.
First off, the KJ190 is a 3-in-1 filter. The thing I'm replacing is just the HEPA part. That's what the F1 filter is. It's 12" x 6.5" x 1.7", roughly. As such, it is almost a perfect width-fit compared to the original, and probably close enough for thickness to match the original. (The original had a good, hard metal mesh on both sides, acconuting for some of the difference in thickness.)
This is an example drop-in of the F1 inside the original filter stack box.
With inner calipers, I measured the gap at 2.2" in the "length" dimension.
There also was a bit of wiggle in the "width" dimension, but that can be solved with my existing insulation.
I have two options for fixing the length. One is to cut something out -- maybe garage door insulation foam, or even a hunk of wood -- to the 2.2" x 6.5" x 1.7+" dimensions. Maybe cut that in half so I have two spacers, and then seal things up with dryer duct tape.
Another is to take a second F1 filter, and hack away a 2.2" piece from it, re-doing the laser-cut solution I had for the KJ190. That would be kind of brutal. On the downside, I'd give up a full filter, and I'd lose about 0.5" to the paper borders. But on the positive side, I'd add 1.25" to 1.5" of extra air flow, compared to just using spacers.
