letters to dark

[Bert Kemp]

what would cause a few letters to be to dark. Baltic Birch 2 coats of clear poly. speed 325mmps power was 40% 2 passes.IMG_20160519_143846947 (Copy).jpg

[Keith Downing]

what would cause a few letters to be to dark. Baltic Birch 2 coats of clear poly. speed 325mmps power was 40% 2 passes.IMG_20160519_143846947 (Copy).jpg

That's strange. I've seen that with inconsistencies in the wood, but not usually high quality pieces.

Assuming that piece is now scrap: If you go just above the letters and do a 1/4" raster-ed line, does the "black" show up there in the same area too?

If so, i would say it's something with the wood or perhaps somehow the poly coat is thicker in that section.

If not, i would say something with your design or possibly the laser that's giving more power or less speed to that area.

[David Somers]

My thought too Bert. Or perhaps the plywood is warped in a way that is causing that due to a change in Focus? I suspect you have already thought of this last idea but just in case......

[Bert Kemp]

doesn't seem to be here.raster line (Copy).jpg

[Keith Winter]

Is that chinese wood or real baltic birch ply? Red hue makes me wonder if it's really baltic birch, as the Chinese use red glue many times. Fake baltic and Chinese wood has inconsistent veneer thickness so you could be possibly going through the wood and hitting the glue causing the change in color or alternatively the redish areas are where you are hitting the glue and the black areas are where you went all the way through the glue.

what would cause a few letters to be to dark. Baltic Birch 2 coats of clear poly. speed 325mmps power was 40% 2 passes.IMG_20160519_143846947 (Copy).jpg

[Bert Kemp]

I'm pretty sure its quality BB heres were I buy it
http://www.woodworkerssource.com/shop/category/6_plywood.html

its pretty deep raster

The actual piece will be Juniper wood solid no glue this is a test piece I'm running a test piece of Juniper now, hated to use it for a test but what the hey.

Is that chinese wood or real baltic birch ply? Red hue makes me wonder if it's really baltic birch, as the Chinese use red glue many times. Fake baltic and Chinese wood has inconsistent veneer thickness so you could be possibly going through the wood and hitting the glue causing the change in color or alternatively the redish areas are where you are hitting the glue and the black areas are where you went all the way through the glue.

[Bert Kemp]

Ok I guess the problem was uneven coats of poly on that first piece
I did a test on poly coated Juniper, bare juniper and bare baltic birch they all came out fine.
Now lets pray the real piece comes out fine also there is no more wood if I mess up

[Keith Downing]

Ok I guess the problem was uneven coats of poly on that first piece
I did a test on poly coated Juniper, bare juniper and bare baltic birch they all came out fine.
Now lets pray the real piece comes out fine also there is no more wood if I mess up

I was thinking the poly was the issue as well after looking at your re-test. Unless there's a possibility the laser was running slower, I would guess that's probably the issue. Let us know how it works out.

[David Somers]

Bert,

I often spray my ply with clear Lacquer to aid in cleanup and avoid any need for transfer paper. Works well, dries really fast and my wood is sealed for any other surface treatment I might want to apply. I use lacquer and shellacs alot in turning along with a few other finishes so I always have some handy. I apply it to entire sheets of ply at one time using a High Volume Low Pressure Sprayer (HVLP....got mine on sale at Rockler) and it does a nice even coat, and quickly does a whole sheet. For whatever that is worth.

Good luck with this next run! Hope you have discovered the problem.

[Don Corbeil]

Is that chinese wood or real baltic birch ply? Red hue makes me wonder if it's really baltic birch, as the Chinese use red glue many times. Fake baltic and Chinese wood has inconsistent veneer thickness so you could be possibly going through the wood and hitting the glue causing the change in color or alternatively the redish areas are where you are hitting the glue and the black areas are where you went all the way through the glue.

+1
It looks like more than two letters are affected. From the picture, it looks like lines 1-4 all have a couple of letters that are darker. I've seen this on certain plys, where the glue underneath is not uniform.