Air assist moves cut pieces

Community Laser Talk
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I have a Sculpfun S9 with air assist. It’s a decent little pump, and I replaced the (cheapo) hose with a higher quality plastic hose from Ace, which really helped.

So the air works pretty well, and it most definitely helps with the cutting efficiency, minimizing the discolored edges when cutting wood, and not having to clean the laser constantly.

However, I’m having a problem keeping the cut pieces in place. For example, cutting with 1/8 basswood, I’m currently using 300mm 60% 4 passes (I can sometimes get away with 3, but 4 works consistently), and as soon as the cuts complete around the parts, some of which are small, but not tiny, the air starts moving the pieces around enough to mess up the cut.

I feel like I could increase the power and decrease the passes, but that’s going to also affect the quality of the pieces, and no matter how many passes, as soon as the pieces are fully cut the air is going to push them around.

This seems like it would be a common issue, but I’ve searched around and either I’m using the wrong search terms, or it’s not as common as I think.

The pieces are designed to be cut adjacent to each other; imagine a jigsaw puzzle (it’s not, but helps to explain). The smallest pieces are on the order of 1 cm x 1/2 cm, and they often fly right off the honeycomb once they’re cut, but this is happening to a lesser degree with pieces that are even more like 1 inch square-ish. Sometimes they don’t quite come out of their position, but they jostle around enough that the last pass of the laser is no longer aligned to the previous passes, which obviously makes for a messed up cut.

How do people cope with this air issue? I’m not sure I’d love to put sticky stuff on the honeycomb because 1) it might transfer to the bottom of the pieces, and 2) frankly there’s just not a lot of surface area on the top of the honeycomb. Any material that I might stick to the wood itself would get cut along with the wood, thereby no longer holding the pieces in place. Obviously any weights or pins go around the edges and can’t help hold these pieces in place with the air flow being at the position of the laser.

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I hope somebody has a workable solution for you. I would try using aluminum tape (the type used for A/C ducts, and not the Mylar tape) because the AU dissipates heat well and likely will not melt. HOWEVER, I have no idea what the adhesive will do in your case.

Am I correct thinking the pieces that move get under the laser and get hit again? Just blowing away from the laser sounds like a good thing. I have trouble visualizing exactly what is giving you grief.

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Tabs are your friend:

You can tweak a couple of non-obvious parameters to get exactly the tabs you want, per a recent discussion:

You must manually cut the tabs to get the pieces out, so you want them as weak as possible without breaking away on their own. This will take some experimentation based on your laser’s power / speed / passes / whatever.

They’re essential for cutting cloth, layered paper, and chipboard coasters.

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Using tabs also has other benefits. By using tabs, the cut pieces do not separate, allowing you to elevate the wood a few millimeters above the work base. When placing wood directly on the work base, it is more prone to developing discoloration, but using tabs helps avoid this issue.

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You could raise your material with spacers above the honeycomb so they drop down before they get blown away.

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Where they’ll get torched by the next pass of the laser beam on adjacent parts. Somehow, they always manage to slip sideways just enough to get under the beam.

Source: been there, done that. :grin:

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Hmmmm maybe only raise it half the thickness so they sink but don’t move sideways is the only thing I can thinkof other than tabs

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Tabs are your friend. You can either have included automatically or manually.
I cut mine .5mm wide/thickness and I set it to cut into the tab a little bit on your finished surface.
Easy , peezy.

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Thanks everyone.

Yes, I realized not long after posting this that the obvious answer would be to use tabs. Unfortunately, this would end up requiring clean up (probably sanding) of dozens-to-hundreds of small pieces every time. Severely affecting the amount of time and labor to complete the end products. Unless I’m missing something else?

It may be that there isn’t really any other good option, but I figure that if there is, this group would know about it!

As ednisley said, if they drop down they can often get hit by the laser again, but it depends on how they drop. For the pieces that are small enough to drop down the honeycomb slots, it depends on which way they bounce (and also depends on whether I have the honeycomb raised above the wasteboard). It makes me wonder if I might be able to set up something where the wasteboard is significantly below the honeycomb, with some kind of container to catch the pieces. Sounds like a bit of a project.

Setting up so the pieces drop like half the thickness of the material is interesting, but there’s enough movement then with the kerf (which is something I was asking about in a different thread) that the edges can get hit again. One kerf width would probably be okay, but with several pieces worth of kerf, enough space gets added up that the air assist moves the pieces around too much. Imagine you’re cutting a jigsaw puzzle. The kerf around one piece isn’t that big, but once you’ve cut several adjacent pieces it adds up. It seems like people who cut a lot of jigsaw puzzles would have run into this problem already.

I’m wondering if I’m simply not going to be able to cut pieces adjacent to each other in a natural way, but that will end up being pretty painful, not to mention wasteful with material.

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Think of it as meditation. :grin:

If you get the tabs exactly right, an Xacto knife blade will trim them off without any need for sanding. Of course, that means they must be cut almost all the way through the material, leaving only the thinnest possible remnant between the parts.

Flip the whole sheet over, slice through both ends of each tabs, and life will be good!

It’s like support material in 3D printing. I hate it, but sometimes ya gotta do what ya gotta do:

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I tried the “elevated same distance as thickness of material” and found that the pieces would pop out sometimes anyway. Decided the best way to prevent was to lower the amount of air in the assist until they didn’t blow out. Actually didn’t take much adjustment.
I am all too familiar with time lost when having cleanup work on small pieces. I eliminated the sanding by using a very sharp knife to cut through the tabs with workpiece turned wrong side up. You can see all the tabs. I do many of setups manually on the tabs. That way you probably could get by with only one tab or two at most.

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One thing that I did to manage this was draw a vacuum on my sheet of material. This was with a big CO2 machine, but I paper-masked off the parts of the bed that would not see material, and then reinforced the bed to prevent bowing, and used the 1hp blower exhaust fan to suck the sheets down to the table.

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I have same issue as well, it is cutting the pieces as they are being blown around… so I have to be very careful of my layout. I have to be careful the ORDER of the cutting, else some pieces blow into the path of the next piece to be cut, and well… oops. Adding tabs doesn’t work for my thin veneers I use for inlays, so can’t go that route. And turning off the blower does work, but causes issues with the burns. Still looking for a good solution where I can keep the air assist on, and NOT get blown over to the next piece…

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My parts can be very small, and veneers are typically 1/32nd or thinner, so I would have to put down a thin small metal screen or so under my parts, so they don’t fall through…and a vacuum box sounds great… I may have to give this a try.

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I’ve been cutting a lot of veneer lately and have been using tabs to prevent exactly what you are experiencing. I don’t have the number of pieces you do so I can feel your pain, though the tiny tabs are super easy to remove with a fingernail, swipe of an Xacto blade or a small piece of sandpaper.

I have used the suction from a shop vac attached to a laser bed sized box covered with 1/4" hardware cloth (wire mesh), but even aluminum window screen will work. Due to the setup time I rarely ever use it compared to my “picking the tabs off” method.

With the shop vac platform, tape off the open areas and provide a method of releasing some of the vacuum so you don’t pull so hard as to distort the bed (it really doesn’t take much vacuum).
For this I teed in a 1" PVC ball valve into the vacuum hose to act as a bleed-off.
If your bed still distorts, you can add supports under the mesh where appropriate.

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So much good thinking and conversation here.

@ednisley and others; it’s possible tabs might work, depending on the material. I have doubts about Xacto’ing them quickly and easily with acrylic (we will be using different materials, and there are still a lot of unknowns). I mean of course it can work, but I’m not into that kind of meditation ;-). It’s also one thing when you’re talking about an individual project for yourself vs. having to make hundreds or thousands of tab cuts every week on an ongoing basis. I want to make sure that whatever solution I come up with scales at least fairly well.

@ferg, adjusting the amount of air is a nice idea. I’m not sure how I’d go about this, but maybe some kind of adjustable clamp on the hose itself might work. I’d vaguely thought about doing something this at one point, but figured the “Goldilocks” level would be so narrow (or non-existent) to have enough air to be effective while not so much to blow parts around. Based on your comment I may revisit this, thanks.

@Colin and brewster, Vacuum on the under side is a possibility when I get a dedicated shop space. I think one could also adjust the suction level by simply selectively covering different percentages of the bed, right?

@shipmodeller, I feel your pain, lol. Yes, I’ve found that order of cut can help with some of it, but not all of it. For what we’re doing, currently working with 1/8" materials, single pieces don’t fly out after they’re cut, the kerf is small enough to hold it in place. It’s only when multiple adjacent pieces get cut that they start moving around. With your veneer, I suspect you’re in an even tougher boat that we are.

What I experimented with yesterday was redesigning the layout and being a bit wasteful with the material. In other words, parts would normally nestle together, but I created a horrible layout that has space between all the parts. In some cases that blank space can be very tight and fairly efficient, but in other cases it was pretty bad. That said, it was the first time all pieces actually cut properly without problems – and I didn’t have to deal with tab trimming (which I haven’t tried, and I do intend to do so later).

Another thought, which I’d like to run past folks, is that I bought a set of limit switches for the S9. I haven’t installed them (the reasons might go in another thread), but I’m wondering if I could use absolute coordinates and simply cut some portion of the pieces on one pass, then pull those pieces out, cut more pieces on the next pass, etc. Any thoughts on this? Will the repeatable accuracy of Sculpfun’s limit switches on an S9 be good enough for something like this? There’s still the possibility of a piece randomly blowing into the path of the beam, but I think on average with careful ordering it could be minimized. Maybe.

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You started out talking wood, where tabs are appropriate.

Now you’re talking acrylic: tabs are out.

In production, your labor cost will instantly consume any incremental material cost, even using volunteer / grad student slave labor.

Space the parts out, cut them in their own little pocket, and move on. The layout might benefit from running it through a parts nesting program, but doing it by hand can probably get close enough to optimum.

In production, do not futz around with the machine: set up the material, run the job to completion, and repeat.

Anything done manually between start and finish just increases your scrap rate.

Sounds like a fun project! :grin:

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I have a gauge on my compressor to read pressure plus a control to change value of output. You will be surprised what a little lower air assist will do.

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Correct - Im sure you could set up a bleed valve to the surface under the vacuum as well.

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Yeah, sorry about the material swap. We’ve been primarily using wood, and this has been the main focus and a real problem. But we’ve also been experimenting with acrylic and it’s still a problem, though the acrylic is a bit more dense, so it’s not a guaranteed failure every time. There’s yet a whole other part of this that will involve etching on metal, but we’ll probably need another laser for that, and I don’t want to distract too much from this topic. I’m early on the learning curve with lasers, that’s for sure, but I’m a quick study :wink:

I’m still going to experiment with very small tabs with the wood, just to better understand how they might serve us over time, but based on your comment I don’t think I’ll even bother with a test run on acrylic. My gut says I’d have to push every part up to a disk sander or similar, and that just seems like too much. Plus, I don’t like being around acrylic dust.

Your next comment about production is spot on. It’s obviously something that’s been on my mind, but thanks for the polite kick-in-the-butt reminder. As I mentioned above, this is the method I used on the last pass, and it went fairly well. The extra benefit of doing it this way is that when it’s on wood I get to control the direction of the grain. There are some other projects we’re looking at where the cost of materials might outweigh labor, but not this particular one.

I also agree with you after a little consideration on not trying to pull pieces during a cut. Partly because of the ongoing issues of material waste, but also it just seems like doing too much of that over time is an accident waiting to happen. And some pieces are still likely to get blown around, even if less than wood.