Hello Alan; This is currently being discussed and if you read the linked discussion and follow the links within it, you may get enough information. I have some plywood images attached to that discussion. My apologies if it is too much information but the background stuff is also useful.
What type of things are you trying to engrave onto plywood? The laser should be capable of burning an image into plywood. I am guessing that you are using an original Snapmaker machine with a 200mW laser beam.
To add my 5 cent here: I did a quick’n’dirty test on wood and it’s crystal clear that natural wood absorbs the laser differently at different densities, caused by the tree growth. Tree rings absorb differently than inbetween. And plywood is basically layers of natural wood, so depending on the wood this effect may or may not be there. Will post a photo later.
And here’s the promised picture. Left the engraving on wood, which I stopped at some point. Right the image in Luban, red rectangle schows the printed part. You can see how strong the wood grain influences the blackening.
The bottom board was my first test, which I was quite happy with.
I then tried some text (some wedding invites) one on the left printed but way to dark, then same file again on the left only this time way to light. Printer was set to 100% power, 1000/1000 work/jog speed
Allow me to ask, how flat is the plywood on the bed?
And what about the height difference across the whole bed and the laser head?
I do not have a SM original but a SM2. I have noticed the same inconsistency when printing on a large 1.5mm plywood. It was due to the wood plate was slightly curved and thus de-focused the laser beam.
Although I could not explain the huge difference between the dark and light result (I assume they have the same setting). You can see on the light one that the top-right section of the wood is most probably curved from the focused height.
PS: allow me to ask, is the dark one vector based generated and the light one grayscale or B/W?
I, too, have had some incredibly inconsistent laser engraving, but just on paper in this case. I don’t have photos right now, but it was all down to the paper actually bowing up in the middle, and thus getting out of the laser’s focus zone. My solution is a thing sheet of steel, screwed down at the corners, and some fridge magnets holding the paper at convenient locations. Which doesn’t help if you have a very even coverage, but in my case (bookmarks and attempts at business cards) would have helped a lot.