Laser absorbent?

Anyone know of a material that can absorb the GF laser energy without much/any damage? I’d pick a metal, except I’m mildly concerned about reflections. Once upon a time, I might’ve gone with an asbestos material but not these days…

Basically, I need the laser cutting equivalent of the “run-off tabs” used in structural welding. In other words, a material that sits off at the start and finish of the laser path, so that I can set the laser to start firing before it reaches my intended target material, and allow it to continue firing until after it’s entirely clear of my target material.

Why? Well, I’m cutting entirely across a material, and given the camera issues I can’t set the laser to reliably fire/stop at the exact edge of the target material. If I set the firing to begin/end off the edge of my material, I get flashback but more importantly I’m leery of intentionally (and repeatedly) firing the laser into the honeycomb without any intervening materials.

…so, if I had small blocks of very energy-absorbent materials, I could set them at the ends of my laser path, and thereby guarantee a clean cut at both ends without also potentially (eventually) damaging the machine itself.

I’m using scrap hunks of plywood etc. right now, but surprisingly enough I may actually run out so a reusable material would be sorta nifty to have in a “I have optimized the irrelevant parts of my life” sort of way…

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Put a sheet of paper underneath it. :slightly_smiling_face:

Maybe a piece of sandstone or flagstone? Slate or some other porous tile perhaps?

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Heh, paper will fix the flashback, but not the “is it safe to fire at full power, low speed, directly and repeatedly into the honeycomb” problem… if it really is a problem. Dunno, but I’m paranoid I guess?

Laser safety sheets, like in laser safe goggles sure does the job…

No…might not work at low speed. You can go with the slate or tile.

A shallow pan of water would work. May not be practical though.

You can’t damage the machine by firing the laser into the hex grid on the crumb tray. The laser can’t put out enough energy to damage the steel hex grid. The grid will heat, and you will get some flashback in certain situations, but the GF is designed so that you don’t need to worry about running off the ends.

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I want something like this too, something that will completely negate flashback by absorbing any laser that cuts through. I use sacrificial cardstock as it stands now, but it would be ideal to have some sort of a reusable laser-eater that won’t reflect. Seems steel isn’t going to do it, or the honeycomb wouldn’t flash.

@shop, any thoughts?

Cool, I’ve sent them a note to see if they’re prepared to deal with the public.

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Same principle as to how the glasses are made, I believe. They are basically dyes that are compounded into polycarbonate, acrylics, etc.

You don’t need to worry about this. I have done exactly what you are talking about and it hasn’t damaged either the laser or the material. There was a slight increase in flashback at the end of the cut, but that can be solved by adjusting your power and speed levels to just cut the material and masking, and then add another layer of masking.
By the time the beam hits the metal bottom of the laser housing it is too dispersed to cause damage, so the only place you have to be concerned is the touch point between the material and the honeycomb, which is what the flashback comes from.
You can’t damage the honeycomb with the laser. It is thin steel, so it dissipates the energy quickly. It also can withstand repeated heating and cooling cycles without damage. That is one reason it is used for this type of application.
Keep in mind that any type of laser protective plastic such as the Gentex material is designed either to reflect it so that the laser does not penetrate the surface, or to absorb a reflected beam. A direct beam will cut the absorptive material, especially if it is plastic, because plastic cannot disperse the energy fast enough.
There are two factors here - absorption vs reflection and heat transmittance. In order to prevent reflection damage to the laser you want a low index of reflection in the wavelength of the laser. This means the material has to pass the laser light without absorbing it or absorb and/or dissipate the energy, so you want both a high specific heat and the ability to disperse the heat away from the contact point quickly to prevent burning of both the material and anything nearby. I am guessing that your best bet would be something along the lines of carbon-carbon tile, which can absorb the energy without damage without reflecting it.

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When building a modern glass or pottery oven what at one time would have been asbestos is now ceramic fiber that even aside from not having the huge medical implications does everything asbestos did and better because it operates at much higher temperature.

We made a blacksmith’s forge from an old truck break drum and rebar and as is the case with most forges if the air blower stopped for even a minute the forge would have to be re-lit. As it was available at that point, we put in an inch of ceramic fiber batting and a thin layer of mullite and when dried cranked it up laid on a slab of fiber and went off for shopping and lunch and when we got back after over two hours the forge popped to life as soon as the blower was turned on!

The stuff comes in batting like fiberglass and a thick paper looking like cardboard but able to stand over 2.5k degrees F. In either case it has almost no inertia when heated and might need welding goggles to watch if you tried cutting it with a laser, it cuts easily with scissors.

It would certainly stop any blowback, it would need something to keep from creating its own.

You could use the Seklema mat folks use to keep paper on the honeycomb. They have a 16x24" size you could cut down if you want to cover the whole bed.

Ceramic fiber batting is also just as skin irritant as fiberglass. I have to move it aside to work on heated beds on 3D printers and I run a filtered fan to keep the dust out of the air, as well as protective gear. The one time I didn’t I itched for three days.

Interesting, but I suspect not the same thing. The stuff I was talking about is designed for 3000F ovens and more expensive than those applications needing less extreme properties. It is almost pure Alumnia powder with as little binder as possible. in any case I handled quite a bit of it and never had that issue, the paper that would be the stuff to use in any case.

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For our friends in Europe there is a number of companies selling foam concrete block. The oldest company is called Ytong. It has many properties not a focus as it is used for buildings, but a low heat inertia, insulation, non cracking from heat, and you can cut it with a hand saw. Ytong and two others made forays into the US but was too high a technology and I believe all have left. I still have several samples I use as a hot trivet or to solder on. I had not thought of it in that way but you could mill out a perfect shape for the heated bed of 3d printers with it.

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This has all been very interesting, thanks everyone! I’ll post something if I’m able to put together a workable solution.

You’re not going to harm the crumb tray with this laser…