I’ll probably be making my aluminium channel bed shortly, but in the meantime, here’s something I noticed on youtube.
The standard Ikea LÄMPLIG Trivet is cheap and shiny
It’s a bit scary shiny for me but worked well for the other guy - I can just see full dose laser beams reflecting off those curves into your mother’s Monet, but nothing a quick dose of flat black won’t fix.
It does work but the slots are a bit too wide, small parts fall though
It also does not cover the surface underneath very well, so you’ll still get burn marks on the bed
Burn marks on the underside of the stock are minimal though
Regarding beam deviation, I did not notice anything , but you can see there’s some kind of coating on the trivet, because there’s significant charring visible…
Also it’s not very large and you may need a set of 2-4, at this point it becomes not that cheap
One benefit of this system though is that you can shine a light on top of the stock after the work is done, and see underneath if it shines through to confirm it’s been properly cut
Have I just got you into trouble?? 
I have 12 metres of 12mm aluminium channel to chop up tomorrow - will post to a new thread when it’s done! 
I use the grid type light defuser material.
It’s plastic and easy to cut. I use screws and washers to hold it down on the 4 corners. If you take your time setting it up, the grid can be used for setting up your parts.
In the laser lab in college. We were told to remove any rings in case they reflected the laser (which was invisible) into somewhere you didn’t want it to go.
Where were you yesterday before I bought my aluminium? 
That’s a neat idea and about a third of the cost of a waffle, plus it’s almost uncuttable by a diode laser.
My funky aluminium grid will be cheaper but will it be better? I think not!
Hiding in plain sight!
@niget2002 David you got me thinking.
(never photograph your ceiling directly into a light source which will show all the otherwise invisible imperfections!)
I’m not sure what you mean by grid type diffuser. Can you drop a link to an example?
Make sure you get aluminum and not plastic. Most plastic ones are polystyrene.
I use plastic, but I have a good vent that blows outside a window.
As of now… I think I pretty strongly advise against plastic.
This evening I was dialling in my 5W CoreXY laser on some balsa… Ran the material test generated by LightBurn on the end.
I was right there but of course with the laser goggles on. Some flickering light is normal when cutting through, so… NBD, right? Smoke smell when working with wood also normal. Then the flames UNDER the balsa were OVER the balsa. Yank the power from the laser (Oh good! The printed plastic is also on fire!) And burning plastic diffuser is splashing onto other bits. Difficult to smother under the laser mechanism…
About 10 seconds after I saw flame, the frame of the laser engraver is on fire, the core of the machine has fallen onto the tray, and is on fire, the shelf under the machine is on fire.
I got everything put out. The machine of course is totalled. I am not even sure which lump of melted stuff is the laser module (probably the big one, but there are 3, each side piece and the core are all lumps of melted goo, and I don’t know which is which, about the only identifiable bits are the shells of the LM beatings.
This took seconds.
Not gonna scrimp when I rebuild, steel tray, snd proper waffle bed.
So my 5W laser module, the coreXY laser machine, one Ikea shelf unit, a sheet of balsa, and 2 spools of filament that were on the shelf beside the machine are definitely casualties. My desktop arcade machine was on the shelf above and now features a smoke finish, but I think it’s OK. An air mattress (deflated) that was beside the shelf unit might no longer be serviceable, and I got a small second-degree burn on my left index finger.
All in all, got off pretty light for a fire, but like I said… plastic light diffuser grilles are something I will never endorse, now.
Noted - the aluminium type however should be OK (and AirCon grilles).
I hadn’t given the steel sheet under the machine a thought (as in I had planned it but forgotten to order) - will buy that tomorrow!
Yep, just make sure that it’s not just aluminum coating on plastic, which is (apparently) a thing…
Wholeheartedly agree.
Note also: PLA burns like mad once it’s ignited. Just something to keep in mind when printing parts that see laser use.
