Help me riddle this, alignment issues

Couple of days ago i successfully aligned the mirrors from scratch, or so i thought. Russ’s methods were used.

Went to cut something big today (900x600 bed) and noticed bad cuts in one corner.

Mirror 1 to 2 beam is dead center and parallel with Y motion.
Mirror 2 to 3 beam is also dead center and parallel to X motion on far end.
However, if i move Y all the way back my beam is HIGH ? How ?

If i turn mirror down where its high, its going to be low on near end.

Doing my head in.

Y rails not parallel to each other ? Spot on on near end, low on far end ?

Am i making sense ?

Have you measured the height from bed to laser head and/or focus lens at all 4 corners? it seem your laser bed plane is not parallel to gantry x/y plane.

Yes i have, all good. Thats why its a riddle.
Its not the focus distance that changes, its beam veering off in ONE corner.

I cant turn mirrors, as if i do it will be low on the other end.

According the Russ method, my tube is parallel to X at one Y end (far from tube) and not parallel at near end (away from tube).

So it looks like the back end of the right hand Y rail is a little low and needs shimming or some other form of adjustment.

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Thanks for confirmation that i’m not crazy. Moved back of rail up - problem gone without touching mirrors. Brilliant. Learned someting new, thanks.

Now that the rails are level with each other you should check the distance from the nozzle to the bed in all 4 corners and center to make sure your focus distance doesn’t vary across the table.

Thats the idea. However i’m in a process of ordering flat steel table cut as i cannot trust honeycomb with this one bit. I always had trouble with focusing properly throughout the size of my HC.

Nozzle to table subframe seems to be ok, but honeycomb over it - focus is all over the place. Not sure how to “level” honeycomb for it to be consistent at all places. Ideas ?

Its not the corners that are the problem, its bits in between. I can measure well on subframe, but honeycomb is -~2mm at places.

Yeah, my honeycomb is amazingly un-flat. I have a special place for it leaning up against a wall where it can do no harm. I hate the thing.

Immediate use now is PETG cutting. Its thin, its floppy - honeycomb is a must.
In near future i expect to cut leather, which is also asking for honeycomb use.
Just trying to figure out how to flatten it properly.

But yeah, i see how people dont like honeycomb. Havent got enough experience lasering to rant on about that yet. Just trying to make damn thing flat. :smiley:

Well if you find a good technique for flattening the thing let me know.
About the only thing I use it for now is the occasional rubber stamp. The stamps usually only cover a few square inches so “flat” doesn’t matter much.

When i had to cut a rolled rubber sheet I used a double sided tape and sticked it flat on a 4mm poplar plywood.

Curious about your shimming method. I have the same problem with drifting spot and I’m sure I need to raise my right rail to create a plane. What material/ technique did you use to get it right at every single screw hole along the rail?