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Extraction is a bit of an experimental area. We can't predict what will work best in advance but we can identify the things that might be useful and problems with the current systems.
On the HPC3020 the extraction is performed by a large fan mounted on the back of the unit. The HPC3060 has a very large free standing extraction unit which moves a much large volume of air.Both of these models suck air out of the laser but have no obvious place for air to enter into the unit so the fumes tend to circulate around the work leaving stains on the surface.
The 3060 also has a tray under the honeycomb, the far edge has holes cut into it in an effort to draw smoke out from under the work piece. It's not very effective because the extraction fan is nowhere near it.
Neither machine provides filtering of the exhaust fumes, although the Nottinghack laser has had some effort put into hacking a carbon filter on the exhaust. More information needs to be gathered about the success of this modification and how other machines deals with exhaust filtering.
There is a more direct option for fume extraction which involves mounting an extraction hose directly to the Laser Head. (see here) This appears to offer good results, except that Andys system does not have air assist through the head and the additional mass to the head might slow the motion down.
To maximise the airflow through the machine, a large extraction fan shall be placed at the back of the machine. Air holes should be made in the front of the machine which could be assisted by a series of quiet running fans (think computer fans)
Smoke should be actively extracted from under the work piece too. This may sound similar to the vacuum table but the fan requirements are actually quite different. This fan needs to provide airflow rather than a vacuum.
Bob Clough pointed us in the direction of this extraction fan. (The ebay auction is over but we should be able to find similar size/price)