Bed for very large fabric laser cutter

I have a home-built CNC machine (lowrider v3) with a 2500x1440 bed.

I want to attach a 5W diode laser to this, in order to cut fabric (for sewing clothes).

I could use some advice as to what to use as a bed for this. Considering fabric is very “floppy”, it needs to be well supported.

I was thinking either a simple flat steel sheet, but off course I’ll be getting a lot of reflection that way.

Or a gigantic honeycomb bed (I can buy a 2500x1250 non-expanded block of 1cm thick aluminum honeycomb quite cheaply: 19.1mm (3/4") Aluminium Honeycomb; 10mm, 20mm, 30mm - Easy Composites).
But I’m assuming a honeycomb of that size will need a frame to support it to keep it intact while manhandling it on and off the CNC?
I also read that there should be room below the honeycomb for the gases to escape, or is this not important for a low power application like this?
And I’ll still need a steel sheet on the bottom to protect the MDF bed of my CNC machine.
All in all, it’s looking like a serious undertaking…

Anyone has any ideas, experience with building a bed this size, or about the simpler needs for low power applications like cutting fabric?

I would think that black steel is the cheapest and best for this task. It can be screwed directly onto your MDF board. On this I put a layer of cardboard which is available in wide, long rolls for covering when painting. If you only cut one layer at a time there are no problems with smoke, with several layers of fabric at the same time I have no experience.
Reflections, I will not be so afraid of, you should always use protective glasses anyway.
But, have you tested whether you can handle the task with a 5W diode laser?, I use my CO2 laser (approx. 50W), with a reasonably high power setting and a lot of speed, then I get the best/cleanest result. This applies to cotton and cotton mixes with up to approx. 25 synetic (viscose) fibres.

This will be … challenging: a low-power diode laser doesn’t have enough oomph, particularly on light- or blue-colored fabric, to tolerate many losses.

The key problem: maintaining sufficient flatness over that huge area, because a millimeter up or down will put the fabric out of focus. Z probing the entire platform for grid adjustment will definitely help, but that implies pulling the fabric flat against the platform, which will likely require running a vacuum through a perforated table.

The 700×500 mm honeycomb for my CO₂ laser has internal stiffening rods and is still floppy-flexible, so IMO your huge honeycomb must be attached to a flat sheet to prevent it from collapsing. Perhaps an integrated vacuum platform with the honeycomb atop perfboard atop stiffeners on an aluminum extrusion frame?

The distance from the top of the honeycomb to the bottom of the vacuum plenum should defocus the beam, but you could make the bottom from aluminum clad foam board:

It’s not going to be easy, but it’ll be fun to watch when it works!

Some previous discussions:

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Hi.

Tldr:
If I was facing a task like that, I’d probably cut it on top of a slightly raised glass sheet.
Raised, for reducing the possibility that the reflected beam ruins the fabric, and for allowing adjustment for absolute flatness.

True, but the edges of the cuts will be charred anyway, so a bit of extra charring shouldn’t matter much?
Easy to try how badly the reflections char the fabric.

However, using a flat steel will be a challenge though because:

+1

The obvious question first:
Do You have the means to expand a block that size at location?
Once expanded, the honeycomb core can’t be moved much before it’s skinned.

At one point I had the idea of making ultra lightweight musical instrument bodies out of 50mm honeycomb and either aluminium or carbon fiber skins, but controlled expanding of the block proved to be quite challenging, and I had only 500x500mm slab (when expanded) to worry about.
That idea was put into the backburner (along with many other similarily wild ones :wink: ), but should I pursue it at some point, I’ll corrugate 50mm wide strips of aluminium, and glue them together to form the core.

In any case, any composite core like that is extremely flexible without the skins by design, it has to be able to follow the possible contours of the skins.
So You’d need a knife edge hatch of ~50x50mm under it.

With a purpose made honeycomb, You’ll get by with ~300*300mm hatch.
Even the galvanized steel 600x600 honeycomb beds droop in the middle wihout support
And a purpose made honeycomb of that size will be guaranteed to cost dearly.

The material being aluminium, it has the added disadvantage of being non-magnetic, makes taking the wrinkles out by tightening the fabric without the possibility to use magnets a real PITA.

It’s always essential when cutting materials that produce flammable gasses when cut with a laser.
If there isn’t adequate ventilation, at some point the mixture will ignite and at least blow the fabric up, ruining the cut, or at worst, light the fabric -and most likely the machine as well- on fire.
And no-one wants that.

Regards,
Sam

:finland:

Flatness shouldn’t be an issue, the bed of the cnc is milled flat with the cnc itself. So provided anything I put on it has an even thickness, and doesn’t warp, it should provide a flat surface for the laser as well.

The honeycomb route seems to be a dead end: too cumbersome, difficult, expensive.

I also have a 600x900 CO2 laser (which is too small for practical fabric cutting). I’ll give the metal plate a try on that, and see what happens, compared to the honeycomb.

@bernd.dk Why the cardboard between the metal and fabric? Just to keep the fabric clean from any residue on the metal? I wasn’t worried about reflections for me, but rather for the fabric (like you always have some charring on the underside of your material where it touches the knives or honeycomb), but I guess the cardboard would help with that as well.

@LSS will the diode laser pass through the glass? If so that seems like a pretty good solution. I could put down a thin metal sheet, have a number of pins on that (a bit like those painter pyramid stands), and the glass sheet on top of that. I’ll probably use a number of glass sheets, instead of a single one, I’d rather not manhandle a 2500x1250 sheet of glass :smiley:

I’ll give that a try on the old CO2 laser as well to compare against honeycomb and metal plate. (Or will the behavior through glass be different for a CO2 laser vs diode laser?)

@ednisley Concerning the power of the diode: I don’t have any experience with diode lasers at all, just with my 80W CO2 laser. Which cuts fabric (even 3mm thick leather) extremely quickly and easily. Which made me think a 5W diode would suffice, seeing as they’re supposedly equivalent to a 40W CO2 laser.
If not 5W, would 10W suffice? I was thinking of getting a Laser Tree module?

Thanks,
Bernard

That would not be fabric laid on a flat surface, at least based on my simple projects:

None of those were ironed, but it was impossible to spread the fabric uniformly flat on the honeycomb surface. The cuts definitely failed atop a millimeter or so of wrinkle, so it’s a real problem.

Also, I tried cutting two layers at a time and that failed pretty much completely, again due to wrinkles and air gaps.

AFAICT, back in the day we’d call that a “lie”, but nowadays it’s just “marketing” or maybe “alternate facts”. :frowning_face:

Different wavelength, different beam shape, different optics, different everything: a diode laser is not equivalent to a CO₂ laser, except in the very specialized world of marketing claims.

Ironing is very much a must! Both before cutting (whether with scissors/rotary cutter or a laser) and during sewing (pressing the seams).

What is your experience trying to cut fabric with a diode laser vs CO2 laser? Should I just drop the idea, or would a 10W (or more?) work?

None; all I have is a 60 W CO₂ laser.

However, judging from what happened to somebody trying it with a 5 W diode, the whole process is right on the edge of not working:

This comment may save you from a few dead ends:

Exactly this. A few times, when it’s a little too cold in the workshop, I seem to “catch” or prevent condensate from getting onto the fabric.
I can control the laser to cut a single layer of denim without cutting through the cardboard.
Very small elements, e.g. inserts for jewelry boxes, I cut directly on my honycomp without visible problems, the advantage here is that you can attach the fabric to the table with magnets.

Hi.

It will.
And You can also laser through glass with visible wavelength laser, another way to ensure flatness with cloth and paper products, and to reduce the amount of oxygen (=cleaner cut) in the process.

Basically, if You can clearly see through a material, a visible wavelength laser will pass through pretty much unobstructed.
Pretty much, because inpurities and additives -as well as any coatings- in the glass will absorb a few percent of the energy.
When lasering through glass, a few percent of the energy will also be lost because of the different densities and optical properties of air and glass, but those losses can usually be fully compensated with either reducing the speed and/or increasing the power a few percent.

Yes, the “pins” should have a soft surface though, glass does not like stress-points.
If You have the glass high enough, You can use magnets with the glass as well.
The underside magnets should be rubber coated and not to be slammed onto the glass with the top magnet for obvious reasons :grinning: .

True, handling (large) sheets of glass gets difficult and dangerous really fast.
Especially under the fabric to be cut, it won’t make any difference whether there’s one or several sheets of glass.
And probably not much if lasering through the glass either.

These:

https://www.wpg.com/catalog/hand-held-vacuum-cups

are Your best friends when handling any flat glass products by hand.
Those plunger style suction cups may seem rather expensive regardless of the brand, but the cheap cam operated hardware store varities will fail sooner or later.
Been there, never again.

:grinning:

Like @ednisley there said, that’s pretty much bollocks.
“Alternate fact” is somewhat accurate statement, because there’s actually a hint of thruth behind that claim.

Because the average focus spot size of a budget 5W diode laser is generally much smaller than the focus spot of a CO2 laser for multitude of reasons, the energy density may well be equal.
Or even signifcantly more if the spot size of the diode is exeptionally small, and the spot size of the CO2 laser is large.

But:

Means that comparing those two different types of lasers by just one variable is utterly fruitless.

I have very little experience in cutting fabrics (just a few tests), but if I were You, I’d probably test (or coax someone else to test :wink: ) the power requirements and the expected cutting speed with a 600x600 bed diode laser first, before purchasing the head.
If I had to make a semi-educated guess, I’d say that while the 5W diode is ok for marking fabric, cutting fabric with any reasonable speed will require 20W or so diode.
The spot size will increase with every additional 5W, but since kerf plays an insignificant role when cutting fabrics, that shouldn’t pose a problem.

Regards,
Sam

:finland:

Thank you @LSS, that’s extremely valuable information!

I see lasertree also has a 20W module: LASER TREE K20 20W Optical Power Laser Module

A little more expensive, but doable. And considering it’s a more modern module, and you get the PSU with it as well, which you don’t get with the 10W kit, it doesn’t seem too bad a deal.

I guess testing cutting surfaces / methods (metal plate / glass on top and/or below) with my CO2 laser doesn’t make any sense due to the different laser characteristics. (I was also under the impression my CO2 laser would actually engrave glass…)

I just did a quick test with a steel plate on the bottom, masking paper in the middle, and fabric on top which cut very cleanly with the CO2 laser.

So it looks like this might be a very easy and cheap solution. Possibly enhanced with a glass plate on top to keep it flat, if ironing and magnets don’t suffice.

It will not work with a CO2 laser, which engraves fine on glass. If you tighten the fabric at the ends and strategically place magnets correctly, it is not necessary either. Cotton is also very uncomplicated for slight variations in focal length.

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