Perhaps this has been discussed but I haven’t seen it.
Are there any potential problems that could arise from having a filter that’s pulling air at a greater rate than the GF is pushing it?
I’m sure @Dan or many others more knowledgeable than I will have the answer…
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Love the design @dan_berry!! I’ll look forward to seeing a finished version!
@jusjus I’m not sure that would work. I have a feeling fumes would escape, which is not good.
@tbelhumer I’m curious about this too.
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The glowforge filter is using hepa and charcoal, so I would see if you can incorporate the charcoal in some way (im assuming the filter you are using is hepa) as to reduce some of the toxins.
No, there are no problems. It’s actually something that would be encouraged, since the hose coming out of the GF is so long and even @dan has stated that the fans on their filter add-on are “significantly more powerful” than the one in the GF itself.
Let me tell you a thing about HEPA. It has become a marketer’s wet dream that lets them prey on people’s fears of pollution and dirty air. In a nutshell, HEPA filters work by providing a random path for particles (smoke, gasses) to impact into and get caught in the filter material as they flow through a volume of air. The effectiveness to do this is a combination of the density and impact surface area of the filter material. But people read HEPA, and they think it’s a magical purification. For a layman’s summary, read this: http://www.cnet.com/news/appliance-science-hepa-filters-and-the-physics-of-fresh-air/
Have no fears, I will absolutely be adding charcoal to my design, I just haven’t got there yet as it’s still a work in progress as I improve my Sketchup skills. But I think you have the purposes of HEPA and charcoal backwards. Charcoal is what removes the toxins, and it’s important to use activated charcoal rather than plain charcoal. HEPA removes the smoke.
ah, I think I must have just written it poorly, as the text in the parentheses was not meant to be the subject of the sentence. It should have read as “incorporate the charcoal in some way as to reduce some of the toxins”. I think were on the same page 
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@JeremyNielsen thank you for your thoughts. The fablab of Munich did
something quite interesting (you might need google translate for this
): diy absaugung - this isn’t that cheap though…
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No problemo. 
But in answer to @jusjus earlier post, I agree with @JeremyNielsen that I think the floor-stand model linked isn’t going to work very well. It’s infinitely better to try to keep an exhaust filter system as enclosed as possible, and that seems pretty ‘loose’. The filter I’m planning to use isn’t branded as a HEPA filter, but it’s not really intended to be. I’m confident that the system as a whole (using an enclosed box, providing toxin and smoke capture) would qualify as HEPA-level.
But if a person is super concerned, FRAM makes increasingly strict (more expensive) filters in the same form factor. The one I chose cost me less than $7 CDN (~$5 USD) from Canadian Tire. It depends if you want to spend more and more money on an issue that’s probably not significantly improved.
Edit: Accidentally attributed comments from @jusjus to @takitus
I wouldn’t be quite so sure. The larger fans in the air filter are probably because of the higher resistance of flow through the filter. Too much pull on the exhaust port might cause a change in air flow pattern within the machine, perhaps drawing the flow away from important places, like at the point of the laser cut. I’m not saying that I know that a large pull from the exhaust port is bad, just that I don’t know for sure that it isn’t. I asked this question in this forum long ago, and never got an answer…
One of the problems with an air cleaner like that is that it acts on room air, which will have a much lower concentration of contaminants than the exhaust air right at the Glowforge. Lower concentration generally means much lower removal efficiency. Also if that is an electrostatic air cleaner it probably acts mostly on particulates in the air and may not do much, if anything, for fumes or vapors.
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Are you concerned that the airflow will cause the intense 40W of focused blazing heat to cool down and affect the cutting of material? I find that incredibly unlikely. A more realistic thing I could imagine is that the material being cut is so light that it moves around like kleenex sucked into a vacuum. Keeping it under 200 CFM shouldn’t cause a problem, considering the distance and volume of air through the hose it has to move.
But naturally, the GF filter has one thing I don’t: access to let the GF laser control the external filter exhaust. From what I’ve read, the biggest benefit is that it turns it on/off during jobs, as required, to lower noise from the fans. I’m not worried about that in the least.
Electrostatic cleaners are capable of doing more than just larger particulates.
Check out https://www.youtube.com/watch?v=x5YFK8mmeRQ
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No, I’m not thinking it would cool down the cutting process, but perhaps redirect the smoke-clearing air away from the cutting location. Again, just blue-sky conjecture. In the extreme case, it might over-rev the cooling fans in the 'Forge and damage them (but that would have to be a MAJOR pull on the exhaust port!). But then again, I have 1000 CFM to work with in my whole-house exhaust system.
Ah… Well then more airflow is exactly what you want. Every laser cutter I’ve seen draw their fumes downward, through the hopper grid. The reason for that is because the smoke and more toxic gases can at best cloud (or at worst, erode) the lenses that the laser shines down through. You want those gases to go down and out, not across the material or up to hit the lens.
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Getting back to cutting a 4" hole in glass, any competent glazier should be able to do this in about ten minutes. I’m not sure if this is achievable with toughened glass though.
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