Invent Design Make

The Problem of Wood Dust – A Cyclonic Solution?

The Dangers of Wood Dust

Lots of exciting making, prototyping and woodworking related activities generate wood dust, chips and shavings that make a mess and pose health and safety problems.  Obviously clearing this out of the way is important, but not just so we don’t trip over or set fire to it.  In the case of finer particles, we need to watch out because they have a habit of turning up inside our bodies and causing trouble, much like an unwelcome guest at a house party that gets drunk, causes a scene and vomits over things.  About 5% of woodworking dust consists of airborne particles that vanish in outdoor air currents without a trace, but when kept indoors they try to invite themselves in.

Looked at under an electron microscope, fine dust contains many very sharp jagged barbed particles. These tiny sharp edged particles also work their way deep into and clog the filters we use to protect ourselves (both the ones on the vacuums and the organic bits of our body).

These particles cut and tear fine vacuum filter fibers, especially when we either shake or blow our filters to unblock them. Human bodies are not protected from the smaller invisible particles, which can slip by our natural defences and get lodged in our respiratory tissues where they cause scaring and release toxins. Woods contains toxic chemicals cause irritation, allergic reactions, asthma, poisoning, and even increase our risk of cancer. Peer reviewed medical studies show that every exposure to fine airborne dust causes a measurable loss in respiratory capacity and some of this loss becomes permanent.  For a recent (2008) review of these health effects check out this doctoral thesis by Jette B. Lange on the subject.

Possible Solutions

After research into fine dust collection, we chose to build a Bill Pentz cyclone separators for the Dust Sniper project. This design provides the gross separation needed to keep fine filters from immediately loading up and more importantly it provides the fine dust separation that minimizes how often we will need to replace expensive HEPA filters and/or lungs.  Ok so two vacuums may not move the kinds of volumes of air needed to get all the fine dust from tools like a table saw, or planer thicknesser, so it is still important to wear a dual cartridge, NIOSH approved dust mask and try to maintain a good outside airflow while producing your masterpieces.  With the aid of this cyclone build though, we can use household or workshop vacuums, which do have an advantage over big dust collectors/extractors, namely, that they have the pressure needed to extract fine dust from tools with smaller ports. 

Good dust collection must get rid of both the large and fine particles. Most vacuums, dust collectors and cyclones provide excellent large particle collection with various levels of convenience, but almost all come with open filters that freely pass the unhealthiest dust. This turns these units into what Pentz rightly calls ‘dust pumps’, that fill small workshops with airborne dust – levels over fifty times higher than found in large commercial woodworking facilities that vent outside.

Only vacuums provide the pressure needed to work with our tools that have smaller ports, but workshop vacuums are almost always difficult to empty and require frequent replacement of expensive fine filter bags. We wanted to minimize our need to empty and replace these expensive filter bags.

There seem to be four main strategies people use to try and intercept dust before it gets to the filters – three of which simply pass the unhealthiest dust right through, which quickly loads up and ruins any fine filters we may have.

1. Cyclonic dustbin lid separators like this (or trashcan separator lids) separate using a combination of drop box and cyclonic action. A drop box works by putting a small pipe into a large sealed space which slows the airspeed enough that heavier items drop out of the air stream. The better of these separator lids add a cyclonic swirling action to this drop box effect to permit using much smaller containers. Interestingly these separator lids get better than 90% separation by weight which is good (we were using a diy one for some time).  But these simply pass the filter-ruining airborne dust right through.

2. The popular Phil Thien baffle that you can add to a traditional dust collector works almost identical to a separator lid with about a 92% separation efficiency by weight. This means it also simply passes the filter ruining airborne dust right through.

3. Most commercially available cyclones provides roughly 95% separation by weight and makes emptying the dust easier than struggling with a vacuum or dust collector. A cyclone uses gravity and centrifugal force created by swirling air to separate. We call them cyclones because they create a small cyclone or tornado inside a sealed cylinder and cone. You simply spin the air inside so the heavier dust particles get pushed to the wall and cleaned air exits out the top. Traditional cyclones use gravity to drop the heavier particles. A good cyclone separator keeps the tornado centered because if it wanders it sucks the dust right off the walls. A well designed cyclone is shaped just right, so that it keeps a fixed airspeed to hold the material pressed to the sides as it drops into the sealed dust bin.  It will also  reverse the airflow right at the bottom of the cone. Reversing the air too low lets the internal tornado suck material out of the dust bin (bad). Reversing too high keeps the larger chips and shavings from dropping which causes the cone to plug (also bad).  A plugged cone, just like a full dust collection chamber, will cause all the dust to move through the cyclone with no separation (very bad!).  Just like the separator lids and Thien baffle ‘traditional’ cyclone designs and most other ‘diy rough approximations’ (like this or this) only separate off the heavier particles and simply blow the nasty fine airborne dust right through.

4. The Pentz based design here provides this much finer fine dust separation needed to keep from pumping the fine dust into (or worse, through) our filters. It smoothes the airstream turbulence to force even the fine particles out of the air then uses a directed air stream instead of gravity to force the particles into the dust bin. In short, this cyclone minimizes filters clogging and minimizes the loss of suction that many casual DIYers experience soon after they hook up their household vacuum, or even their dedicated dust extractor to a woodworking tool.