Uneven engraving color


#1

I’ve been doing a lot of wood engraving on my new GF, mostly with proofgrade maple ply. I did the one in the photo for a friend of mine, and this is the latest of several similar ones that show a certain unevenness in the engraving color. I’ve noticed on these wood engraves that once I brush off the soot and residue there are sometimes lines and areas of uneven lightness that don’t seem to be caused by wood grain or whatever natural variations you might find in wood.

My settings were 800 speed, full power, and 340 lpi, doing an engrave from a solid black and white high-res image, with no grayscale or gradients of any type. The vertical lines under the word “patrol” bother me the most, since there’s no way those are because of wood grain. So do any of you more experienced users have any idea what I might be doing wrong? I’ve been cleaning the excess residue off with a kitchen scrub brush (no liquid - even denatured alcohol was making my pieces warp). I see other engraves on this forum that look perfect, so I’m assuming this is a case of operator error. So what am I doing wrong here?


#4

Deep engraves usually do better on solid hardwood, rather than the plywoods, since the real wood is just a layer on outer faces with plys. I cannot judge how deep you went from the picture.

But for eliminating the char from either, Fast Orange and an old toothbrush will certainly work.
There are also Fast Orange wipes that remove resin and char from cut edges, but the toothbrush phase works best inside an engrave.

Barbecue planks can be used if want to go on the cheap, but there are many sources of 1/4 inch hard wood slabs, usually like 6 x 24 or less.


#5

Not terribly deep - maybe a little more than a millimeter. I wasn’t totally thrilled about working with ply for that exact reason you mentioned, but these circular cutouts are 9" across, and ply seems to be the only proofgrade item wide enough. I played around a bit with Baltic birch ply just so I wouldn’t ruin my proofgrade sheets, but though it’s fine for experimenting, it certainly doesn’t cut it as a finished product (total Russian roulette as far as the mystery knots and imperfections that lay under the top layer). I’m starting to feel like part I of my newbie mistake is even trying to get consistent results from ply. There’s a good hardware/woodworking store near me - maybe I should see what they have in the way of wider hardwood sheets.

As far as the Fast Orange cleanup goes, once you’ve scrubbed the char off with FO and a toothbrush, how do you rinse off the sludge? I tried FO on a smaller engrave I did on proofgrade maple hardwood, but it warped on me. I assumed it was because of the water content in the FO. Once again, I may just be doing something wrong due to my inexperience, but I’m a little stumped. Any advice would be appreciated.


#6

The Proofgrade plywood is fine, as long as you don’t engrave through the veneer.

Higher LPI values cause the laser to burn over areas it has already travelled over, so the burn goes deeper. If you reduce the LPI to 275, you will not cut as deeply with the beam. (270 is my favorite setting for engraving on the plywoods, and it corresponds to the SD setting. Also, your speed is a little slow - that’s going to cause charring. Try bumping that up to 1000, or just use the default SD Graphic setting.


#7

OK, thanks. I’ll try the 270 setting. I’m not trying to go particularly deep; just enough to give a sense of dimension will do. I’m much more interested in maintaining a consistent color in the engraved areas - at least as much as the natural irregularities in wood will allow. Any tips on how to rinse off the Fast Orange sludge without warping the wood?


#8

Mixed results with warping (thickness matters), but currently I wipe up the majority of the fast orange debris with a dry cloth or paper towel, then whisk the entire surface with a 3 inch paint brush until the little damp looking areas in the cracks look dry, and that seems to clear any pumice left over without introducing any further moisture to the design.
I have used alcohol sprayed on a cloth, but that has a possibility to warp as you mentioned.

When it did//does warp, I have gotten good results by lightly spraying alcohol on the other side (non engraved back) and then wrapping it in a paper rowel to absorb excess moisture, then placing it over night under a flat board with a 10 pound (4.5 kg) weight on it.

Since devising that 3 inch brush whisk method though, the warping is not an issue like it was when I was using alcohol as a final cleaning.


#9

Tangentially related; I’ve been purchasing 8" wide strips of basswood from http://www.nationalbalsa.com. The price is reasonable compared to local retail and the quality has been excellent.

One issue with hardwood engraves is that the grain can become quite obvious in the engrave.

You can sort of see it in the leaves/feet of flower dude on this box.

I’ve been meaning to do some experiments with deep engraves that I then fill with a solid pigmented filler of some kind. Epoxy, perhaps. Or maybe just a thick layer of paint and let it dry for a long time.