CNC Plasma Cutter Filter Gets The Slag Out

No matter what kind of tools and materials you use in your shop, chances are pretty good that some process is going to release something that you don’t want to breathe. Table saw? Better deal with that wood dust. 3D-printer? We’ve discussed fume control ad nauseam. Soldering? It’s best not to inhale those flux fumes. But perhaps nowhere is fume extraction more important than in the metal shop, where vaporized bits of metal can wreak respiratory havoc.

Reducing such risks was [Shane Wighton]’s rationale behind this no-clean plasma cutter filter. Rather than a water table to collect cutting dross, his CNC plasma cutter is fitted with a downdraft table to suck it away. The vivid display of sparks shooting out of the downdraft fans belied its ineffectiveness, though. [Shane]’s idea is based on the cyclonic principle common to woodshop dust collectors and stupidly expensive vacuum cleaners alike. Plastic pipe sections, split in half lengthwise and covered in aluminum tape to make them less likely to catch on fire from the hot sparks, are set vertically in the air path. The pipes are arranged in a series of nested “S” shapes, offering a tortuous path to the spark-laden air as it exits the downdraft.

The video below shows that most of the entrained solids slow down and drop to the bottom of the filter; some still pass through, but testing with adhesive sheets shows the metal particles in the exhaust are much reduced. We like the design, especially the fact that there’s nothing to clog or greatly restrict the airflow.

Looking for more on CNC plasma cutter builds? We’ve got you covered, from just the basics to next-level.

[Keith O] gets the credit for this tip. Thanks!

10 thoughts on “CNC Plasma Cutter Filter Gets The Slag Out

    1. Ha. I was thinking it was rather strange to not make it out of metal, considering a shop with a CNC plasma cutter would almost definitely be able to build that much more easily. Surely he has a welder too. I guess metal pipe is expensive if you can’t manage to just find it lying around.

    1. The greater the turn radius, the heavier the particle has to be to be thrown out, so tighter turns would dump smaller particles than the wider ones would be capable of. Therefore you’d want the smallest last, not the biggest.

      I wonder though, if one could make the equivalent of a “fractional distillation” column for suspended silts, dense/big stuff out at one end, less dense stuff at the bottom.

      1. As [Todd] says it might actually be better to have larger sizes towards the end to get a sufficient flow through the filters. A pretty complex problem to try predict accurately, even more so when its hard to know how much suction/flow at the table will be needed – if the plasma table surface is mostly covered the airflow through the system looks like it will be very much worse than working on small stock.

        I wouldn’t worry too much about turn radius if you intend to stack them – even the widest turn radius will catch some of the lightest particles. Which makes me think best results would probably be with a relatively wide radius setup so you don’t need to crank the fan power up too much. I would think anything smaller than used here would be too restrictive to stack practically at all while perhaps even as much as double the radius used would still filter similarly well. But that’s based on nothing but intuition and back of the envelope style low precision guestimates. Be interesting to see it tested.

        Though ultimately if its taking in enough air at the tool and then exhausts away from the operator its a huge gain even if the filtering is not hugely effective.

  1. I am wonder if a vessel under the working level full of water could be an option. Of course the gaseous fraction still should be ventillated outside, but most of the solid particles fallen near verically probably would stuck in the water bath beneath. (At least it is my guess …)

    1. Water baths are traditionally how CNC plasma tables handle this, and I’m kind of surprised to see someone taking a different approach here. Seems like way more hassle, cost, power, and noise to use large forced-air blowers instead of a simple pool of water.

      1. Of course, you are right. I was just kidding a bit in my post. :-) The water pool is widely known solution of the given problem. (It was a surprise for me too.) I wanted to know if any other reasonable motivation to go on this different way.

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