A laser cutter bed has to be robust, fireproof, and capable of adequately supporting whatever piece of work is being done on the machine. For that reason they are typically a metal honeycomb, and can be surprisingly expensive. [David Tucker] has built a MultiBot CNC machine and is using it with a laser head, and his solution to the problem of a laser bed is to turn towards the kitchen ware store.
The answer lay in an Expert Grill Jerky Rack, a wire grille with a baking tray underneath it. Perfect lasering support but for its shininess, so it was painted matte back to reduce reflections and a handy set of clips were 3D printed to secure the grille to the tray.
We like this solution as it’s both effective and cheap, though we can’t help a little worry at the prospect of any laser cutter without adequate enclosure for safety. Having been involved in the unenviable task of cleaning an encrusted hackerspace laser cutter bed, we also like the idea that it could be disposed of and replaced without guilt. Do you have any tales of laser cutter bed cleaning, or have you found a cheap substitute of your own? Let us know in the comments!
Is there any reason for not using more cheap Materials like Sand, Gypsum, Grog (clay)…
I design industrial laser cutters, and I think one reason there is for not using that sort of stuff is that sand would be blown away by the air or whatever assist gas coming out of the laser nozzle, and might be an explosion hazard depending on composition and what slag is mixed into it. You also have to support the material but leave room for the molten dross to eject out the underside of the material, if you are not cutting wood(even plastic melts into strings). Also, the sand would stick to the back surface!
My machines though use a clever trick to always cut over open air while supporting the material, so the supports are never contacted by the laser, and it only ever hits a concrete floor 4feet below, where the heat is far less concentrated. Unfortunately that design is patented, but I am sure the intrepid home user could come up with some non patented way to have a moving support under the material so the head is always over open air.
Oh, and sometimes Laser equipment uses something called a beam dump. I bet you could build one for a 40w co2 laser by repurposing a metal water cooler block from AliExpress, and just running ice water through it with a decently speedy pump, if you can figure out a support that stays steady with the head.
Personally, I’d probably look at clamping the edges of the material and move it around as the motion axes while leaving the head stationary over a beam dump. That would be far less fussing with mirrors to do a CO2 laser. Probably less expensive to build if you need less optics and bellows for the beam delivery, too.
I did exactly what you’re talking about with a 180 w RECI laser tube. It’s 72 inches long and it’s straight up and down with the laser pointing directly at a movable XY table, the Z axis controls the focal length. No mirrors whatsoever.
Cheap yes, but say goodbye to leveling and laser focus I guess.
“that it could be disposed of and replaced without guilt.”
how is disposing and replacing this any different guilt-wise from any other solution? It’s still a bunch of steel coated in matt black paint. I’d also worry about the black paint flaking and leaving shiny spots for the laser to reflect off of and bounce around the room.
You could dip it in hcl, gives it a matte finish the can’t come off
A good idea, I think.
But is it necessary to paint the grid? In the correct cutting conditions, the laser has a small residual power after passing the material. In addition, after any reflection, the beam will be defocused and will not be harmful.
And on the other hand, the coating can leave the tracks on the bottom of the material.
With similar semiconductor laser I use stainless steel sheet and I have no problem with marks by reflection about the pad.
I soak my filthy honeycomb in a solution of warm water and laundry detergent (Persil) overnight. Then gently rinse and air dry. So far, no damage noted to honeycomb. Works well on carbide saw blades and router bits too (manually dry and lubricate after cleaning, though).
I use granite tile, unfinished side up. Can be leveled and utterly indestructible. Can be gotten at Home Depot for as little as $9 per square foot.
Good point…. even 60 watt lasers barely scratch the surface of a granite tile used to put cups and glass ware on.
In my case, an advantage of honeycomb or otherwise highly porous support is to enable better airflow for gases to be removed and for air assist to reduce recirculation of smoke around the operating parts of the machine. Without air handling, I think the tile bed sounds like a great idea.
But can it be used to laser dry jerky?
I use a matt ceramic tile as the laser bed. My low power diode laser works well on this fire proof platform.
What about light diffusing grills commonly found in office overhead lighting?
Those grills are cheap plastic, that can barely hold together under their own weight. Adding objects, and guaranteed cuts from the laser, and it would surely fall apart.
If is any good for you guys, I am using a AC condenser. They comes in different measuring that fits any laser bet. Give it try, you will not be disappointed.
I don’t have answers, but some questions: [1] assuming that the choice of emission frequency does not affect cutting properties, is a laser’s “dot size” inversely proportional to its cutting ability (i.e. the smaller the dot the better the cutting)? If so, then a 10W LED laser with 1/4th the dot size of a 40W CO2 laser (of “unity” dot size) will cut “equally” (given the stipulations) speed, right? [2] I heard that laser cut speed and life are greatly affected by how much “smoke” is emitted (more smoke results in less cutting efficiency). Also, reflections can “feedback” into the laser and reduce its life. So maybe it’s best to use not a fan, or even a robust fan, but a compressed air blower to clear the work area quickly.
I’m sure that industrially, these answers are proprietary, like too much knowledge. Even back in the 16th century, mathematicians would keep “secret” their special knowledge of math so they could get the “good sponsors” to pay them more.
Dot size is related to power, and that’s why you focus your laser. You can’t arbitrarily make the dot size smaller, though: it’s diffraction limited (and likely related to the quality of your optics and coherence of your source as well).
https://www.edmundoptics.in/knowledge-center/application-notes/imaging/limitations-on-resolution-and-contrast-the-airy-disk/
I work in the laser industry designing cutting equipment. No it is not proprietary, I have actually written blog posts on it for my company website.
So here we go:
1. There is something called a diffraction limit that is driven by laser wavelength, so the first thing to keep in mind is that the wavelength does matter, but visible light diodes like blueray or a red laser can actually focus to a smaller spot size than a CO2 laser.
However, that said, you are on the right track! The specification you are looking for is the “energy density” of the spot. For example if your spot has an area of 1cm², and it is a 10 W laser, then the energy density is 10W/cm². So, if you have a beam that is 4cm² in area, but 40W, you would expect it to cut at the same speed, just over a spot 4times the kerf(cutter diameter). For some of the lasers I work with, which are Nd:YAG fiber lasers, at 6kW, the beam diameter is 0.004″ or 0.1016mm, which is 74,007,196.6 W/cm², so not too shabby!
2. As for smoke, what you have is that smoke in the beam path will absorb some of the light energy as you are cutting, and it is wasted heating up the smoke instead of the wood or plastic or whatever. So yes, this is at least partly true. Different wavelengths however are opaque to different materials. A CO2 wavelength for instance can be opaque to polycarbonate, so regular safety glasses can be sufficient in some cases for protection, while a fiber laser requires special dyes added to the plastic to block the harmful wavelength. Similarly, a CO2 laser can produce a plasma ball that blocks laser light from reaching the material to cut it, while a fiber laser can penetrate the plasma to cut even if there is a plasma ball created. So, the smoke may have more effect on one color laser than another.
As far as back reflection goes, yes, light that reflects back up into the head can cause heat to hit components. Generally speaking, this is bad for laser diodes to be heated, and sometimes can even melt nozzles and things if the heat is reflected at an angle instead of straight up. Aluminum and copper are especially bad about this. One trick for copper is to oxidize the surface so it is dull green prior to cutting, and polish it up later. For aluminum, like aluminum foil, use the dull surface up to have better luck than the shiny side. Also, industrial lasers have a back reflection shutoff to prevent overheating damage. It might be good to mount a temperature sensor somewhere close to the action, like stick to the nozzle, and cut power of the laser gets too hot. Otherwise it will be a costly replacement to have to make!