Let’s talk about fans

I found a lot of mentions of fans, theoretical or currently being used, in various threads, but I still have a lot of questions and I think a consolidated topic on it would be helpful.

I’m only on day 2, but the smell is becoming a problem. I’ve gone over everything with foil tape, but my lungs still smell like hurty. It’s a short run and there are only two bends in it, and I’m going to try semi-rigid duct and flexible foil tape to ensure I get every possible hole and crack covered. But still, I feel like I want some extra help from a booster fan.

I’ve tried to narrow it down to 4" 200 CFM inline duct fans, and I’ve come up with two possibilities: Tjernlund M-4 Metal Inline Duct Fan looks good to me and with Prime I could have it here for the weekend. But then I saw the Fantech FR 125 and the words leak-proof caught my eye. I’m going to be going through a lot of trouble to seal everything tightly, so if my fan leaks I will be rather unhappy. That Tjernlund looks pretty solid, but it’s certainly not advertised as leak-proof. On the other hand, the FR 125 is only 171 CFM, and I think the Glowforge is 200. So now I have some questions:

  1. Is it reasonable or safe to have a booster fan at all? I have read some comments about the fan driving (or over-driving) the Glowforge’s own fan, and that being bad.
  2. What airflow is appropriate? What happens if it’s slightly more or less than 200?
  3. Can I keep running it for a bit after the Glowforge finishes to help pull out the remaining odor?
  4. How likely is a fan like that Tjernlund M-4 to leak? Can I get away with it, or tape it up?

Normally in these situations I would just experiment, but these things aren’t cheap enough to just get a few different ones and see what works best. So are there any fannage experts out there who have all the answers?


i don’t know any of the answers, but for what it’s worth, you could have the fantech by the weekend, too.


It looks very similar to the fan I got, and would be likely to leak at the housing seam. Best if you install it at the exhaust end of the run, however you can seal it. I used silicone.


Could there be some holes in your exhaust line?

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I saw your setup from the live stream and I can’t believe it’s the glowforge fan lacking oomph. My setup is all downhill, and yours is up, so it is possible when the glowforge winds down you have a column of odor in the duct that flows back through the machine.

But first, when you put the duct on did you slide a couple of rings of it onto the coupling and then tighten down the clamp? What I mean is did you scrunch up 2-4 rings of the ducting and then clamp behind those compressed rings? The end of my flexible ducting was a bit frayed/torn so if I had only clamped on the very end of it I think I would have had leaks.


This is key. It’s unlikely the hose is leaking. What will leak is the joints and the seams in the metal ducting. (You could use PVC as your ducting but then you have a static issue you’ll want to deal with but there are no inline seams.)

You want to use the foil tape (not duct tape) and use it on any joint - that includes the seams where the pipe is joined to itself as those are usually foldover joints and not leak proof. People tend to focus on the joints where the pipes & hoses connect and miss the seams in the pipe. And foil tape is 100 times better than duct tape for this purpose as it will really seal it smell-proof :slight_smile:


Sounds like he is unusually sensitive to the smells so any amount of leaking is likely to be a problem. The vent connections were my primary source of odor, and the only source when the unit was running. Easily fixed. But after the fans stop there are a few places in the GF unit itself that can allow residual smoke to exit. Only an additional fan or allowing the internal fans to run for an extended period will create the negative pressure needed to remove residual odors.

I might add that the GF itself is not sealed in such a way as to keep internal smoke from escaping through very small gaps once the fans shut off. It was never intended to be a fully sealed unit except to laser light. It is about as tight as could be expected but the fans themselves are needed to ensure an internal negative pressure compared to the room. Giving the user runtime control over the internal fans is the easiest solution.


i agree; dan has mentioned at some point that they’re looking into something along those lines. for me personally, i’d like to see a toggle setting that lets you, say, leave fans running for X minutes after a cut or until the lid is opened.

but assuming these come soon, i’ll probably also be getting a booster.


FWIW, and assuming the hose isn’t leaking somewhere, I found the worst smell resides in the smoke residue on the masking material. Removing that promptly and putting it in a Ziploc bag pretty much eliminates any remaining odor.


Entirely possible. I’ve manhandled it a bit, and it seems to be a flimsy material. I’m planning to replace it with semi-rigid anyway, and that might do the trick on its own.

I don’t think it’s that. I guess in my head if I put a fan right at the window, my gut feeling is that it would be more “pulling” than “pushing” so anything that’s tempted to escape would get sucked out. Or maybe I’m just overthinking it and thorough sealing is all it takes.

It’s clamped a good bit behind the frayed end, and then taped around, and then I did the best I could to tape where it attaches, although the foil tape doesn’t bend that way so I made some release cuts and tried to ensure any gaps were still covered with multiple layers. Butyl tape is on order for the next attempt.

Not sure what you’re talking about here. The Glowforge comes with a single length of dryer hose. I do have a window with this style of vent, so I taped up the foldover joint on that cuff where it attaches, and around the flange. Here again I think I will be able to do a better job with flexible tape.

Yes, please!

I need to do that. I just threw it in an open trash can.

These are all good tips, of course, but I’m still planning to buy a fan. :slight_smile:


Do you get the smell when the job is running or after a job is complete?

I have asked those questions and my ticket was closed as un supported and was zero help what’s so ever… Was told to go read the forum

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Yes. Although it’s hard to tell at this point because it builds up and lingers for so long. I’m trying again to air the place out so I can answer that question better on the next run.

Also, I just realized I forgot to include pictures in my last reply so I’ll dump them here.

I’m also going to tape up that quick-connect coupling, as it’s an obvious source of leaks. This started out as a test to see whether it would leak or not, but it’s too hard to pinpoint the source so it seems like just going nuts with the tape is a better approach.


Do you have access to a Flir or any infrared cameras? might help pinpoint the leak.


I finally got my odor issue under control by using semi-rigid hose with rotating flanges, caulking the flange seams with silicone, then carefully taping the connections. Hose clamps over the flange+tape.

As part of troubleshooting, I performed short-range sniff testing (put my nose right up to the connections) to determine where fumes were escaping.



That helps very much. It helps just to know that it’s possible to run this thing without significant smell issues. It was unclear to me for a while whether everyone just puts up with it or whether some people have gotten it under control (or maybe just don’t have functioning noses).

Honestly I’d put up with a decent amount of stink to have something as cool as a laser cutter, but I’ve literally only done half a dozen cuts on mine, just maple and one tiny bit of acrylic. Even though it’s noon the next day and I’ve been out of the house for 5 hours my throat is still burning. I do seem to be sensitive to smoke – despite not having any (other) allergies, someone smoking a cigarette on the sidewalk upwind of me gives me the same burning sensation. But I think it’s not just me, it’s a pretty strong stench now.


That’s the place most people miss. It looks sealed but it’s not really. The foil tape is perfect for sealing the ducting joints - it’s non-permeable but duct tape doesn’t seal nearly as well (which is counter-intuitive since it’s called duct tape :slight_smile: ).

You may find welded piping for your replacement where the seam along the length is welded but usually you’ll get stuff that’s flattish packed and has a clip together seam. That needs to be foil taped.

Once it’s sealed, @rpegg is right - the residual air in the machine is going to be the big culprit. Since the honeycomb goes all the way to the bottom of the tray, it traps smoke under the material and it usually only gets released when you take the piece out of the forge. Letting the fan run longer and if it’s negative pressure even when the lid is open will draw that smoke back to the exhaust when you open the lid & pull the material out.


I got quite excited when I read the thread title.:crazy_face:
Only slightly disappointed, as there’s useful advice here.
Thanks all.


Something else completely that you could do in case the odors are a problem for you is to keep a smaller recirculating filter fan by the Glowforge. There’s lots of demonstrated evidence that in a small area, having a charcoal HEPA-like fan constantly filtering the circulated air will eventually capture the odor. So although you will be pumping the majority out the duct, the lingering room air is also taken care of.


I have a Honeywell AirGenius 5 (with a fairly fresh charcoal prefilter) turned up to max and running continuously. I was quite surprised when I came home from work yesterday that there was still a smell lingering in there. Now I’m wondering how much of that is from the masking tape I left lying around.

I left the air cleaner on and a window open today, so I’ll find out tonight whether it smells like walking into a meth lab. I don’t actually know what a meth lab smells like, and now that I think about it, it’s probably not like a combination of burnt maple and melted plastic.