Material "swelling" data - the sequel

There seems to be a lot of “tribal truth” about material swelling due to humidity, which reputably causes issues cutting cleanly on the GF. I don’t believe this to be the case.

For reference, I posted this thread back in June, where I presented evidence that it’s not an issue. This thread provides further data. Note that I live in Atlanta, GA, USA. Humidity here in the summer is brutal. Plus we’ve had record rainfall in the past few months.

If my samples didn’t “swell” after 4 months exposed to GA humidity, yours aren’t going to indoors.

Right after that thread (June 1), I printed four sets of sample “chips” from Baltic Birch, Proofgrade Maple Ply and Draftboard, and placed them in different locations. One set was left on my GF (adjacent to my material storage shelf), one went in the car port, one on a window ledge on my deck exposed to all elements, and another was vacuum sealed and left alongside the set on the machine in my workshop.

Here are the before and after measurements. The only one that “swelled” was PG Maple Ply, and that was by <1/100". EDIT - the draftboard left outside also swelled a little.

The sample chips (note how bleached the DB was after 4 months in the sun):


I guess the question is - was there any cutting variation? Something can “swell” as in less air pockets/heftier material without noticeably getting larger (see almost any kitchen sponge)

Great data!

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They were cut side-by-side from scrap material, and are 1/4" wide. I’d say they are close enough to be considered “equal” for the purpose of this test

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I mean if you cut them now do they cut through with the same settings, or do the “aged” ones require a bit more oomph? (I’m guessing no, but that would be the data point)


Good idea!

Three cuts thru each of 4 chips, my own BB settings, plus default PG settings for Maple Ply and Draftboard. The Maple Ply left indoors in a controlled climate (~50% humidity all summer long) was the only one that didn’t cut thru. The draftboard pieces had a little “snaggy” peice connecting them, but they dropped out with hardly any pressure.


As this came up in the other thread, I probed them all with my moisture meter. The chips from the car port and the ones left on my GF all read ~5%. Everything else was virtually 0.


BB showed no change with some pretty drastic temp/humidity tests.
Draftboard clearly has an aging issue - but it seems to have nothing to do with humidity.
and Maple plywood with the worst error - of course being ply that could be the same draftboard aging issue - and also clearly not a humidity issue.

I wonder why draftboard ages poorly! I use very little of it. I wonder if the glue gets harder with age or something unrelated to the wood parts.

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The whole reason I posted the original thread, then did this test, was because the draftboard from a “weather sensor” enclosure I made a couple of years earlier and had hung outside had not changed. I think the glue that bonds the material is not susceptible to humidity.

I also live in the Atlanta area and had an experience earlier in the year that demonstrated the problem with PG Draftboard. My Glowforge is an air conditioned shop and I have some used draftboard also in the shop…
Next to my shop I have an office where I have my computer and unused draftboard. The office is temperature controlled through the whole house HVAC system and humidity controlled through a dehumidifier.
I tried a fairly complicated project from a free laser designs first using parts from my (high humidity) shop and parts from my (low humidity) office. No problem cutting thru either samples. The problem occurred in assembling the parts. The parts from the high humidity shop were mostly impossible to assemble, even with a hammer, but the parts from the low humidity office went together easier without excessive slop.


So then we’re back to square one. If it’s not the humidity, and it’s not the glue - then why can you no longer cut cleanly through DB2, 3, & 4?

If the material is swelling, it’s becoming less dense and should cut better, not worse. The problem isn’t the dimensional stability of the material, it’s the water content. Try and laser cut a wet piece of wood, bet it doesn’t cut as nice as a dry piece of wood.

3D printing has this problem, too. The filament is hydroscopic and when the noodle hits the hot-end at 200ºC that moisture is instantly vaporized, and it leaves bubbles and spatters in the print.

That would be covered under the humidity/moisture reading, and didn’t seem to make a difference.

Is it swelling or warping? Warping might make it more difficult to cut through due to poor laser focusing. Unless pins are consistently used this might be the issue. When I make with warped material, it is much more difficult to put stuff together. Even the slightest warp on finger tight joints can be difficult.

I had wondered if this was a thing and if it affected the cutting at all. Thanks for the info!

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