Vacuum tray replacement for cutting lightweight materials

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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Aha now that I know where to look for static pressure ratings this one would slot in with no modification and provide about 5x the vacuum:

https://www.digikey.com/en/products/detail/sanyo-denki-america-inc/9CRH0412P5J001/7622262

Question is whether or not my mesh would withstand the increase. I can math it out now. 0.03 psi * 11” x 19.5” yields a total ideal downforce of 6.4 lbs. adjusting for efficiency issues (leaks, etc) I’d suspect it’s closer to 6 lbs. Using this new fan would jump it up to 30 lbs. It’d probably work, I’d think.

And yeah a nice small high pressure centrifugal fan would be nice. I looked but didn’t get too far.

This is even higher:
https://www.digikey.com/en/products/detail/sanyo-denki-america-inc/9CRJ0412P5J001/13245514

0.34 psi static pressure. ~74.6 pounds of total downforce. That sounds like overkill for my mesh.

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Surprise, my fan arrived as twins!

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Imagine if the force on the paper was 75 pounds instead of six?
You have me thinking that “supports” of zig-zaggy aluminum flashing aligned with the airflow and correct height glued down could provide that push back to keep your top surface from sagging like that,

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Twins! Congratulations!

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What everyone else said. if you don’t want to do the labor, maybe hire someones to do the work and ship it and you keep a commission. but the minute you do, someone will copy it and do it for less. and a patent wouldn’t be worth it, if you could get one. still a great idea.

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I wish I were that cool at any age.

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be who you are and don’t give a damn what anyone else thinks.

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Yes… In moderation.

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“Moderation is for monks. Everything to excess!”

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Amen

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Moderation in all things (including moderation).

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Skater tangent: Pretty sure those two were in an H-Street video back in the day.

@evansd2
This thread is sofa king amazing. I need this thing. I’ve removed my fan, so I’m thinking I’ll just plug it in and use the GF for power (i have a basic)… And yea, the sagging issue I think can be solved with properly cut (with lots of holes?) and positioned supports. I’m confident my inline fan will still remove smoke fine, but as you said, it’s paper and isn’t going to smoke too much.

This really is a brilliant idea and GF needs to get in the game. Well done Man.

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Excess! Started with the one red blower (1.5hp Penn/850cfm)), then decided to add a leftover I had from another laser (not a big one, like 400 CFm),… then decided I needed another big red one, so a total of two 1.5hp blowers.

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This is a cool idea because the Glowforge would trigger the fan on and off as well. One thing to watch for here though if you do it is a potential discrepancy in the measured height vs the actual height for when vacuum is applied.

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