Engraves - vector vs bitmap, and SD vs 3D

(I don’t know if this post belongs here in Problems & Support or if it should go elsewhere. Feel free to move it if I put it in the wrong place!)

A while back, we lost one of the pieces for our old copy of Ricochet Robots. Now that we have the GF, we’re working on making our own set of pieces! I’ve started drawing shapes, and was deciding which parts to engrave, which parts to color, etc. I first made a vector file in Illustrator, and tried engraving it. For all of these, I used the ProofGrade Medium draftboard.

This was my first time with any kind of grayscale (previous engraves were just a single shade), so I wasn’t sure how it would work. My shapes were grayscale (not RGB or CMYK) filled between 10% and 85% depending on how deep I wanted the shapes. Here’s that one, using SD graphic:

It’s hard to tell, but there are three depths. Going from the outside in: First is the hexagon border, set to 25% gray with a depth of 0.01". Next is the main hexagon, set to 10% gray but with a depth of 0.03". Finally, the star is set to 85% gray and is 0.075" deep.

I’m confused why the main hexagon is deeper than the outer hexagon border, even though its shape was only at 10% (but the shallower outer border was at 25%). Any ideas?

Next, I took that shape into Photoshop and made a bitmap. I first tried lightening the two hexagons and darkening the star, to hopefully not cut as deeply. Maybe I should have left them as is, because the engrave barely made it through the coating paper! Here’s the engrave using SD graphic:

At the same time, I also cut a version using the new (to me) “3D Engrave” setting, which seems to use variable power. Here it is, before I peeled off the cover paper:

Pretty neat! But when I peeled off the paper, it looks like not much made it through:

The two hexagons were at gray levels of 20% (outer) and 6% (inner).

For comparison, here are all three together:
Three-varieties-IMG_4181

Are there settings or materials which can get different depths of engraving with OUT charring the material? (Again, I used the ProofGrade Medium Draftboard for this test.)

Also, I didn’t notice other comparisons of some of the results between raster and vector for engraving, so this may be of interest to some people. (If I missed others, please point me at them – my search was not exhaustive!)

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Could it be something in the file? Any of the elements overlapping?

For the vector version, in Illustrator I made a hexagon, then made a larger one, then I used Make Compound Path with the two of them. I then copied the whole thing, and in the copy I made a copy of the compound path, pasted it on top, and UNmade the compound path, deleted the outer hexagon, and changed the fill of the inner one. I just double checked the file, and there is no overlap (except the line defining the boundaries).

Here is a screenshot of the image:

Since the inner and outer hexagons exactly border each other (the outer one is the compound path), I was wondering if somehow when engraving the GF somehow took the inner one as being added to the outer one (since it always starts at the outside as it scans across).

In my own limited tests, the Proofgrade 3D Engrave settings appear to be designed to produce minimum depth. I recently did a very similar project, and here is a post comparing the Proofgrade settings to manual 3D Engrave settings.

Bottom line, if you want to go for depth, you need to go manual.

Are there settings or materials which can get different depths of engraving with OUT charring the material?

The laser removes material by burning it away, so the answer is “kind of but not really.” You can experiment with doing 2 or 3 passes at lower power. This does seem to help but best case, your material will be brown and rough instead of black and crispy.

Here is what poplar looks like with a manual full Pro power 3d engrave. Speed 250, I stopped early because it was going to catch on fire. Speed 500 was not much better.

3 passes at speed 750 produced a much much better result.

Also, if you want good 3d carving, get yourself some basswood, it comes out much nicer than draftboard/MDF.

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I asked about not burning because when I did manual settings to engrave on cardboard (settings found elsewhere in the forum), it seemed to just blast away the removed material without charring what was below it, leaving a regular cardboard brown.

Good to know - thanks!

Are the depths listed here the measured depths of the actual engravings? Or the focus height set in the operation?

If it was the focus height, you are defocusing the laser, not specifying the engraving depth.

If they are measured, then I suspect you have overlapped the inner and outer hexagons. I know you said that wasn’t the case, but it might be helpful to post a zip file of the SVG to let folks give you better assistance.

What is your desired outcome here? Primarily depth differences? Or visible color differences? For depth, you should be able to get good results with 3D engrave using a PNG source file. PNG is also a a good choice for the other engrave settings, as it will not have to do multiple passes over the same area just to get one pass of engraving.

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Those are the measured depths. It was with a PG material, so I let the GF automagically choose the focus depth.

Here is the SVG file, which includes two copies: one that includes the inner shaded area, and one that does not:
stars test

Since the version without the inner area printed out as expected, I think that shows that it doesn’t fill in the center. But maybe there’s a bug where GF interprets a hollow filled shape as not being hollow if it contacts a second filled area?

Looking at your file (by the way, this time I think the relevant parts made it through Discourse OK, but Discourse modifies SVG files that are just directly uploaded. If you had something with sizing issues, or a number of other oddities, uploading them as a Zip file will let us see the exact file contents you work with locally) you are correct that the outer hex border and the inner hexagon are separate objects.

You will, however, get double-engraving where the star overlaps both hexagons.

I loaded it in the GFUI. There are 5 operations specified in the file. Three engraves defined by the different colors of the objects. and two cuts, defined by the different colors of the two stroked vectors.

An important thing to realize about vector engraves: The color of the fill does not matter and does not affect the resulting engraving. These three shapes were all engraved using the same settings.

The Stars are more deeply engraved because for most of their surface, they are being doubly engraved: once by the hexes and once by the star.

Also, the last operation there, the cut formed by the hairline outline of the star. Did you set that to score or engrave? My guess from the first picture is that it was also set to engrave, providing yet a third pass over the star–since converting a stroked vector from cut to engrave makes it the same as a filled vector.

To have the Glowforge interpret color differences as visual differences, whether by dithering (SD-Graphic or HD-Graphic) or by varying the laser power (3D Engrave or “vary power” manual engrave) you must supply it with a raster image.

Yes, the lowest power levels on 3D engraves do not get through the masking. When using the manual engraving settings for vary-power, you can set a minimum power level to use for any color that is not pure white (pure white is always treated as “don’t engrave here”).

It may take you a couple more experiments, but hopefully this will give you a better idea of how the Glowforge is interpreting the images.

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@johnse Thank you for the detailed reply!

The outline of the star was set to Score, since I was hoping to make the star well-defined against the other elements.

You wrote:

So you’re saying that there is not (yet?) a way to get multiple levels of engrave depth via different grayscale levels for vector fills? That’s annoying. I can always convert those parts to bitmap, but it adds a couple of extra steps.

Not quite. If you first select SD-Engrave, for example, then Select Manual Engrave instead of Proofgrade Engrave, it will show you the values it will use for the default. You can then change the speed and/or power to change the appearance and/or depth.