Engrave to specific depth

qa

#1

As I’ve been writing up designs, it has occurred to me that there will be times when I want to engrave to specific depths (for things like inlays or creating slots in dowels). I know that GF will use grayscale to determine how deep to create the engraving. Ex: if I cut some nice shapes out of hardwood veneer that is 1/42 inch deep, I’ll want to engrave the same shapes into the base material so that when I glue in the veneer, it will be flush with the top of the base layer.

So, I wrote up a little javascript app to give me the RGB values of the shade of gray that I’d need. You can play with it here: http://ferociousmellow.com/?pg=grayscale.

Here’s the gist of the logic - are my assumptions correct? Would getting the percentage (desired depth divided by max depth) be the way to calculate the right shade of gray?

var blackAlphaAsDecimal = 255;
var percentage = desired/max;
// NOPE, fixed line below - var resultAsDecimal = Math.round(blackAlphaAsDecimal * percentage);
var resultAsDecimal = 255 - Math.round(blackAlphaAsDecimal * percentage);
var resultAsHexidecimal = (resultAsDecimal.toString(16)).toUpperCase();
if (resultAsHexidecimal.length == 1)
{
resultAsHexidecimal = “0” + resultAsHexidecimal;
}
result_RGB_Dec = “(” + resultAsDecimal + “,” + resultAsDecimal + “,” + resultAsDecimal + “)”;
result_RGB_Hex = resultAsHexidecimal + “” + resultAsHexidecimal + “” + resultAsHexidecimal;
result_RGBA_Hex = result_RGB_Hex + “FF”;

Another assumption I make (when entering in what I think is the maximum engrave depth) is that Black (255,255,255) will be .25 inches. Will that always be the case? If I’m engraving into a material that is 1/4 inch thick, then wouldn’t Black be a full cut through the material? If not, then how do I know what “maximum” is?

screenshot of the little app:


#2

That looks like it might be handy. :relaxed:


#3

Of course, just after posting it, I think I have the logic backwards… thinner slices need to be closer to white, not closer to black, so I’m reworking the logic - will post when that’s done.


#4

here’s the correction… I’ll edit the orig posting to show it there too:

var resultAsDecimal = 255 - Math.round(blackAlphaAsDecimal * percentage);


#5

I know they are working on something similar for their treatment of the grayscale, but sadly that’s all we know so far. (No details yet on how it’s going to work, and I don’t really expect any until after they ship…they’re working their asses off to finish up and get those things out the door.)

I’m not sure that you can count on the full depth of engrave for black being exactly 1/4" at all times, because IIRC the depth of the engrave is a function of power and speed settings to a certain extent, and you would have a different 100% setting for 1/8th material versus 1/4" material. (Does that make sense? This kind of coding is a bit beyond me.)

But hang onto this for heaven’s sake - it might make a great plugin, and once they ship out, you can ask more details on how they are setup for the calculations. Or maybe @dan will put you in touch with whoever did the coding if it’s still proprietary once they release.


#6

The program, it seems to me, allows for the maximum depth of engrave, in this case 1/4", to be changed to suit the material… Maybe the maximum depth in a particular hardwood is 1/8", enter .125 in the fist variable, et voila!

Hope this helps.

Thinking about it, the GF’s maximum engrave depth may be more a function of the focal length of the beam than the material being engraved, nothing to say multiple passes can’t be made to reach a required depth. Mmmm, I’ll think on it some more.


#7

Yeah, I didn’t word that right…I guess what I’m trying to say is that there might need to be something to do with speed and power settings too…it might not just be a function of focal distance.

(But I have no idea.)


#8

To get depth it’s going to be a function of power, speed, and material.

The greyscale will determine power, but you can vary depth by engraving at different speeds.

Different materials will obviously vaporize at different rates. Foam faster than acrylic etc. Wood has different densities so dark grain will vaporize less quickly than light grain.


#9

You are right, that’s me always jumping in without thinking it all the way through.

I suspect it won’t be a problem with proofgrade materials, your GF will have the right settings ready to go out of the box. Other materials? Like most unknowns, a bit of empirical investigation will be needed.

The Higgs boson was a theory until it was “observed”. They’ve been a bit quiet on that front lately.


#10

I left this out from the last post, but another variable you might want to include is passes. Sometimes to get the depth you want you’ll have to do multiple fast engraves because the material can’t handle a slower high power engrave.


#11

Does that cause you to think that it might not be acting the way they thought it would? (chuckle!) :wink:


#12

I think it might even be a little more complicated than this for some materials. The fact that (just for an easy hypothetical) 50% power at X mm/sec gets you 1/8" depth in some material doesn’t mean that 100% power at the same speed with get you 1/4" , or that 25% power at that speed will get you 1/16". (I know from playing with diode lasers, for example, that if you move the laser over a very thin wood surface slowly you get a through cut, if you move slightly faster you get a line of char, but if you more faster than that you don’t get any mark at all) So there might be a threshold percentage below which no engraving happens, and then the depth increases from the, but not exactly linearly.

Maybe multiple passes, may some kind of algebraic function.


#13

I figure it’s got to be a lot more complex than any of us suspect. :neutral_face:
(Otherwise we would probably have seen it already.)


#14

Depth is always less accurate on an absolute level than height or width, since material density can vary. It’s fairly predictable with acrylic, but not so much with natural woods, as mentioned.

If you want to engrave to a single depth, you don’t need to specify a color - just set it on the print preview page. If you’re 3d engraving, then and only then will black pixels be full depth, 50% grey be half that depth, 25% grey a quarter of that depth, etc.


#15

:squeeee::squeeee::squeeee:


#16

I should add this is for Proofgrade materials - we can’t estimate the proper power settings for a given depth with non-Proofgrade materials.


#17

That’s okay…the part that has me squeeeing is the ability to tell it to engrave at a roughly specific depth. (Necessary for mortise and tenon work.) :grinning:


#18

Can’t wait to see this in action!!!


#19

Thanks to all. I’m a laser newbie, so all of this detail, all of these factors to consider, is exactly what I was hoping to learn about. So glad the proofgrade materials will be newbie-friendly :relaxed: , and for the rest, if getting a specific depth is important, then I can play around with test pieces to find what works.


#20

So, the way I hear that is if you pick deep engrave, 50% gray goes in 50% of the deep engrave depth. If you pick shallow engrave, it’s 50% of a smaller depth? Or is there just one “engrave?”