Work positioning

I put some tape near the origin and then ran the laser cutter along the X an Y axes to show the 0,0 point. Then I cut some square section aluminium tube, drilled it and then positioned over the tape and spotted through onto the aluminium bed. I then drilled and tapped the bed with M6 and bolted the tube to the bed.
Now I can palce my work at the origin repeatedly and get the cut correct every time. I realise you could do this with a red laser dot but I don't have one and this seemed the simplest solution.

Working well but the odd problem

Having changed the bed for a sheet of flat aluminium and put in an adjustable table, things are going well. I am using honeycomb to put the work on and that works fine. However, when cutting white card or paper, I get a browny/orangey deposit left on the honeycomb which sometimes is transfered to the work. Not an issue for some things but for white card, not pretty!
I am cutting hardboard, MDF and thick card bjut need to do several cuts to avoid a very blackened cut surface. I keep a record of speed, current, material and thickness for every cut I do so that it makes setting much easier.
If anyone has any helpful tips on anything I have raised, then feel free to post them.