Great minds! aluminum foil high five
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Darn. I missed that in your earlier reply.
I’ll take the high five anyway.
I think you might have inspired me to do this. I’m taking 2 weeks off to end the year I’ve still got bits of paper floating in the machine from last time I cut paper.
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I was thinking aluminum flashing. Foil might melt, flashing would not. Might make the the whole bottom and two sides in flashing if I can get the bending right.
I am thinking 4" fan pointing up
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I considered this. It could work for sure. I’m not sure you’ll get more static pressure but you can definitely get higher cfm.
There’s a breakpoint in terms of how large the fan can be versus how thick your box can be, otherwise you’ll see diminishing returns as the air is impinged.
https://www.amazon.com/dp/B07PHRLWTD/
Good example, almost the same power draw but 5x the airflow. It’s 38mm thick, which leaves you at most a 0.5” gap to stay under 2” total height. I’m definitely not saying it can’t work but that was the sort of restriction that led me to abandon it and go for a 40mm solution. I wanted the fan to be enclosed in the vacuum table. You could theoretically fit a 50mm fan mounted horizontally but I didn’t want to bump up to the physical limits like that, so 40mm is where I landed.
As for flashing… I think heavy duty kitchen foil is plenty to stop the excess laser, and easily replaced if need be. Much easier to work with than flashing.
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Not strong enough for structure but you already have that. It is very soft and easy to bend Only hard corners might be tough. I also have flashing already 
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What a cool idea! I love paper … and awesome ideas!
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This is tremendous. I’m always having paper escape during cuts. Brilliant.
Also I’d love to see some paper projects!
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thanks
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your results are amazing!
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This is awesome! Wish I had the skills to make one myself.
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Got mylar? I would love to know if the little cut bits on a detailed design would stay down while cutting with that gadget of yours. I could send you some…
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Another incredible example of what is possible if it can be imagined - bravo 
I’m sure you’ve considered this, since you’re a rather critical thinker, but what’s to stop you from having your power/fan box being attachable and detachable to vacuum boxes of different sizes? I suppose it’s easier to have jigs to cover the excess areas, and definitely would save space and money, so there’s that…but having it be modular would be pretty neat.
Your design also has the benefit of elimating any sort of bow that paper gets when placed on the regular crumb tray. I make all of my earring holders in my machine, and occasionally the small fraction of focus height difference will cause the engraved areas to be lighter or not as sharp, due to my laziness of only using magnets to stop the cardstock from moving. I also rarely deal with flyaways as I very slightly under power the cuts so they can be perforated and pop out fairly easily.
This is a project that I would love to make, but as I mentioned, my laziness will impede me from ever taking it on, though your examples are absolutely tempting 
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This should be marketed as an upgrade for the 
@dan
I’d purchase a second crumb tray with this installed.
Brilliant project!!!
Thank you for posting!
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Nothing, really, except it’s more labor and materials. If I really wanted to do this I could just make smaller screens to fit on the fullsize tray.
As you say it’s really easy to have “jigs” to cover the excess area, a couple pieces of printer paper gets the job done.
The tricky part though is that my mesh does flex slightly. As you pull the vacuum, you can see the mesh pull tight and there’s a bit of a “dip”. So you trade one unknown concave or convex bow for a known slightly convex bow. I haven’t tried to measure the deflection yet, I’ve been just ignoring the variation and using set focus to get the exact height locked in.
A more rigid solution like a honeycomb would be great, but see above in the thread for the reasons why I didn’t pursue that. Alternatively McMaster has a lot of mesh and perforated steel options, their high flow perforated steel solutions were a possibility, but they’re more expensive and have larger holes than I wanted. I decided to see how an inexpensive steel mesh would work before committing to the possibly overengineered solutions you can get there.
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So there is a break point where the downforce generated by the amount of vacuum I’m generating isn’t enough to stop the air assist from taking bits for a ride, it all comes down to surface area. Generally, the smaller the surface area, the less downforce is generated*, and eventually the forces generated by the air assist (assumed to be constant here) will simply overpower it. I’ve found that for a standard printer paper, pieces that are .25 square inches stay put reliably, half that size and it’s 50-50, much smaller than that and they blow away – there’s only so much this rig can hold down.
All of that is to say that the material isn’t really the X factor, Mylar is no lighter-weight than the tissue paper I tried. If you’re cutting extremely fine pieces the air assist will probably give you trouble no matter what lightweight material you’re using.
* It’s a bit more complex that that, because the shape of the part also matters. A piece that is 10" wide by 0.05" tall is 0.5 square inches in total area. By my earlier statement you’d expect it to stay put, yet the end will probably try to lift up. I’m still figuring out what’s going on here, but here’s my current theory: The problem is that the air assist brings its full force down in a small area under the head, whereas the downforce is distributed across the entire piece. So, when the air assist hits the end of your skinny rectangle only a very small portion of the total surface area (and therefore the vacuum downforce) is resisting the assist fan, and it may not be enough to keep it from lifting up or blowing away. This could be mitigated with stronger vacuum, but see above for some of the downsides to a very strong vacuum.
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Lol, I’m a mathematician, not an experimentalist by trade, but it sounds like with so many variables, you just have to try stuff to see if it works. Wouldn’t it be cool if the suction could move with the laser head, so it countered the air assist fan consistently…
I’m thinking I’ll work on engineering ways of holding the stencil material down onto the crumb tray for a while before actually building a suction tray, but … I do love making tools. And, those paper cuts you did sure are fine and delicate. We’ll see.
Anyway, I’m looking forward to see what you make with it.
Yeah I couldn’t resolve this one. Too much happening and not enough data. Add to that the fact that the vacuum will change as you lase material away and it just gets to be too much.
… have you seen my latest terrible idea?
Aha! I found data sheets on the two fans I mentioned.
The one I am using generates a paltry 0.03 psi of vacuum.
The actual air assist part generates a fair bit more, closer to 0.05 psi:
https://www.mouser.com/datasheet/2/632/THA40x40x20-515731.pdf
Now to go see if I can find a better option.
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Probably want to look at a centrifugal fan, huh? But I guess you’d have to run a separate way to direct the air out.
The vacuum bed one is one of my favorite things about the Trotec. It’ll pull warped 1/4” material down flat if I cover up the unused portion of the bed (and printer paper works just fine - though I usually use thin chipboard).
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