Laser Cutters/Engravers use Subtractive Material Processing
Laser cutters and engravers work by removing material from the workpiece. The CO2 laser beam is a high energy single wavelength/frequency of infrared electromagnetic radiation with all of the radiating waves in sync. That, and its’ sharp focus instantly vaporizes the material, which in turn, produces dust and a sticky vapour. The beam leaves a kerf (a narrow slot) when cutting and an indentation in the surface when engraving. It is critical to remove that material from the workpiece as it is being produced if a clean cut/engrave is to be achieved. The vapour/dust can weaken the laser beam as it shines through it, and the material can coat the lens and mirrors which also degrades the strength of the beam. If left on the lens and mirrors it can cause premature damage and they will need to be replaced.
Extracting the Lasered Debris
Removing the debris is much easier if the laser is completely enclosed in a box. Fortunately, the Rayjet50 is in a very heavy box!
Two methods are commonly employed
- Directing pressurized air through a small nozzle directly at the focal point of the laser on the material. Obtaining a clean cut requires this. It is typically not used for engraving. The Rayjet50 has a built-in air nozzle that is controlled in the Rayjet Manager.
- Using an exhaust fan to pull the air in through vents at the front of the laser enclosure and out through the an exhaust port at the rear. Given sufficient air volume, this extracts the dust and fumes as they are created. Trotec sells an air exhaust/scrubber accessory that cleans the air before putting it back into the room. This is an effective, but very expensive, option. Definitely beyond my budget.
I needed an affordable solution…
Determining My Extraction Requirements
My Rayjet lives in a temporary (two years and counting) home in my basement. I’ve been venting it to the outside through a no-longer used chimney. I’ve been using a 600 CFM dust collector from Busy Bee Tools, which does an excellent job. With only a few hours on the laser, the inside of the collector is already coated with a sticky layer. I’m assuming that is happening in the chimney as well. Most likely it is concentrated at the bottom of the chimney as the air would rapidly cool and the vapour get deposited quickly. Now that I’m aware of that, I need to fix it quickly. The solution needs to stop the dust and sticky vapour before it enters the blower and the chimney.
The laser will be moved sometime in the next few months to a workshop in a separate building. Once there, I intend to vent into the shop. That sets up additional more stringent requirements. It will need filtration in the sub-micron range to extract all particulate matter before it enters the shop, in this case a HEPA filter. It will also need active carbon filtration to remove odours.
Clearly two sets of requirements, one short term and one long term. I wanted to design and fabricate a short term solution that I could upgrade to a long term solution. I also expected that this version would likely be a prototype and I might need to fabricate it with different materials for the short and long term versions.
I did extensive searches on the internet in general, and YouTube. I found a variety of solutions, many of which didn’t seem to me to do much filtering. It seemed that the more effective solutions used stacking filters as is typical of commercial systems. I wanted to rival commercial systems in effectiveness and efficiency. It has to remove all dust/vapour/smell while not reducing the air throughput in the laser.
The Design
I decided on a modular solution. Essentially a set of stacking boxes that pulled air from the laser into the top box, and down through the stack of boxes, each with a filtration component, and out through the blower at the bottom.
For short term solution 1, filtration would be only to remove dust and the sticky vapour before it exited out into the chimney.
For long term solution 2, additional filtration boxes would be added at the bottom of the stack to make the air safe to exhaust back into the workshop.
The drawing illustrates the modular approach. Filter boxes can be added and/or modified as needed. The air collection box and the exhaust box do not have filtration. They provide a gap between the filters and incoming/exhaust air.
The Solution Prototype
The prototype is built entirely from 3/4″ (19mm) plywood, pretty much exactly as the design drawing. The inside length/width dimensions are sized to fit commonly available furnace filters. The thick filter box uses a stack of filter media/pleated firnace filter/filter media. The filter media comes in large folded sheets and is cut to fit. The thin filter box has a pleated filter. Over time I will experiment with different filter types, including R12 Roxul insulation as the top filter.
The final system will have an activated carbon (charcoal) filter at the bottom of the stack. That may be loose granules or in sheet format. The 2nd stage up will be a HEPA filter, possibly of the type I use in my Venmar Air Exchanger. Above that, filters will be selected based on the results of this prototyping exercise.
The images below show the prototype. I used a rubber door seal around each box to prevent leaks. The utility of that will be determined as well.
