One of my sources for plain unprinted cardboard is Costco. (I imagine BJs and Sams have the same routine.)
Pallets of product - frequently the product has pallet-sized cardboard sheets between the layers to add stability to the block. Some corrugated, some thin 1-ply.
I’ve found them on food aisles; but the biggest yield is from the paper towels, napkins, and bathroom tissue.
Also, near the checkout, my local Costco has BINS of cardboard boxes of differing thickness. These printed, usually. Produce is a big supplier of those, though not exclusive at all.
Just ask somebody if you can haul away, and they are delighted for you to take your pick.
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Most cardboard is pretty well marked up, so easy to track the source of the board. But those of you pre-cutting the cardboard may benefit from this tip:
Keep your stock organized by source! There are myriad different types of cardboard, and while many work phenomenally in the laser, some are VERY prone to catching fire. One of my primary vendors at work uses this cardboard style, and I had to go through my incredibly dis-organized pile of collapsed boxes to prune out all of their material so I do not have a student use some of it when I am not paying attention.
The benefit aside from fire-prone formulations is that if you want to do something like the Globe Lantern, you want to have a large supple of similar thickness and corrugation spacing cardboard lumped together.
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Yes, if you are paying attention like you should be, (even after the novelty has worn off) a damp rag or even a piece of one nearby might come in handy.
I would like to hear more from people who have experience igniting materials.
I wish I was that organized in my space. I had begun hoarding Prime boxes. And even ordered some really large items (rain barrel most recently) and was beginning to process them for the glowforge. … then the news hit. I had to cut them down further so they will fit in my tiny k40 I got a few months back to fill my ‘instant gratification’ need created by the glowforge. What could not be used for whatever reason went into a spare paper shredder and then into my compost tumbler. I can’t wait to get the glowforge because I have a ton of materials that are too small to position in the k40 and I hate waste. I am glad I got the cheap Chinese cutter. It’s going to make the glowforge an even sweeter gamble. Plus I have s head start. Made enough from friends to make up for almost half what I paid for the k40 without even trying.
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If you take out the standard insides your can get a good 13x12 space in there. The head won’t do the whole 12" tall but it makes it easy to buy & cut stock. I use a lot of 12x12 stuff in mine.
I took out the bed that came with it and made up my own out of aluminum plate and some different sized MDF spacers for stand-offs. I also took out the exhaust intake - it eats up serious amounts of room.
Like you it’s taken care of the instant gratification need 
You guys have to post some pictures for us! Im dying to see what youve made so far!!!
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I already removed the exhaust hood in the bed so I could load the 12x12 sheets. Took the bed out to install the honeycomb and purchased but have never installed the rotary attachment. The k40 is to get my feet wet with lasers and I will likely keep it after the gf arrives. Just to cut and engrave more experimental items. It is going to the garage once the gf graces the place.
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I’m rather jealous of all the organized people on here. While I love it when things are organized, my mind mass doesn’t allow me to get there. Every time I think about it frustration kicks in and I find some other task that needs attention.
Here’s one shot of some cardboard I’m keeping. There are other similar areas throughout my garage 
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Mine is in the garage. The GF will go in the basement when it arrives. I am still doing just flat stock but I have thought about the rotary attachment. With the GF delay I may go ahead and get that so I can expand my learning opportunities 
I also use a larger bed 60W laser at my local Makerspace when I need to do bigger pieces so the delay doesn’t hurt me any but I do like being able to just work at home vs driving a half hour in each direction. Other than material size, there’s nothing the K40 can’t do that the GF can except maybe faster since it’s got more power. For $400 it’s been a good learning tool and I’m even able to do things that folks have a problem with the Makerspace laser - that software is wonky too. The biggest reason I went with the GF Pro is the real software supported by reasonably local people, not a factory that’s got the software as a secondary thing to sell cheap hardware.
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In rural areas “the garage” sometimes means a different thing than it does in suburbia. My garage is unattached and unheated unless I start the wood stove. Now I would never put the Glowforge in an unheated space, but I was wondering if there is a recommended antifreeze additive for a K40 or other lasers with external cooling. Mainly for storage safety since I would never run one in the winter out there for fear of thermal shock.
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I have read that you can use RV septic tank antifreeze in the k40. I have had no trouble at all with just tap water. It’s relatively clean in there. No bugs can get in to muck it up. I do have the benefit of having a heated garage because the room inside the garage has been converted to a laundry center. Newly sporting the largest washer and dryer available to the consumer market. I’m not joking. At 6’3" I can fit inside the dryer with room to spare. So you know who called dibs on tornado preparedness. Surely I jest. Or do I?
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I was super impressed by everyones collection of cardboard. So i spent a bit of time pondering where i could get my hands on some. I figured that i would have to dumpster dive at some local stores.
Then I walked into work this morning, had a solid “ohh yyAAAAaaaa” moment.
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Woah!! What a score! Lol,
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Life is good, when you work at the box factory… lol…
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Haha I wish. We ordered all of it to do some testing on a box cutting/folding machine we designed (not my team, unfortunately). those pallets are actually one continuous piece of cardboard folded on top of itself. I even found a couple that are 20" wide, and ive got the pro on order
but once we burn through it during our acceptance test, my seemingly endless supply will end. Hopefully i can snag some scraps 
(or an extra pallet)
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My garage is attached to the house but it’s a single door 2 bay so every time someone drives in or out there’s an 18 foot hole opening up in the wall dumping all the heat out. Even with insulation, etc., when it’s below 0 (F) nothing’s keeping it warm We had some cold days this winter.
I run Dowfrost for antifreeze. It doesn’t have some of the rust inhibitors, etc. that are fine in an engine or water system but not good in a CO2 laser tube. If you’re only storing it though, then most any antifreeze would be okay as long as you get it pretty flushed before using the laser again.
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I was thinking about your specific situation and remembered a trick for keeping large spaces from going sub-zero. Keep a couple large tubs of water in the space, and until those tubs freeze completely, the ambient temperature is locked at 0.
Unfortunately, no good for you since the water in your Glowforge would also be freezing at zero while the tubs do.
So you would need to RAISE the freezing point of those water reservoirs. Only way to do that is to pressurize it though. So if you could pressurize a bunch of water in containers that are thermally conductive, in theory you could keep such containers in the garage and temp-lock it somewhere above zero (well, at least stabilize above that point pretty decently).
Nothing I have tried, and I don’t know of a suitable container. But it could be interesting.
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Interesting!
So a light bulb suspended above the surface of those tanks would keep the room temperature at 0?
Interesting indeed. Wonder how big the water tank has to be. Maybe not huge (35gal drum?) if I left an immersion heater of sorts in it. Or would that just consume the same energy I’d need to heat the space to freezing?
Only if the light were giving enough power to keep them from freezing, and thus giving enough heat to just keep the room warm, making all the random tubs of water pretty pointless.
The water is like “temperature inertia” It makes it so there is more stuff in the room which is at room temperature, and thus more heat needs to be lost.
The whole reason those large doors cool the room so fast is because the air simply blows out. Well, the water will not blow out so fast. Those tubs stay behind and warm up the new air that came in.
This won’t prevent freezing, just delay it.
@jamesdhatch: Right, would be the same energy to heat the tub as to heat the room. You are just kind of making the room bigger in terms of heat mass.
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