How does the laser know when it's cut material deeply enough?


#1

I don’t have my GF yet to satisfy my curiosity, but my in-head design ideas are getting stymied by this question.

I plan to cut completely through material as well as cut grooves into material.

If I want to cut a .25" deep by .25" wide groove into, say, delrin, how do I tell the laser to cut only .25" deep? How does it not cut deeper than .25"?

Similar question: if I want to cut all the way through a .75" thick piece of delrin, does GF know when it’s all the way through because I told GF it how thick the material is that it’s about to cut?

(Perhaps it is I who am/is/are thick.)

Thanks to anyone who can answer this question.


#2

You can’t - not directly anyway. It’s not like a CNC toolpath definition where you specify the depth of cut.

You get depth through the application of power - more power equals deeper engrave or cut. You get more power by raising the power or slowing the speed. Or a combination.

So you need to test - create some calibration designs to try in your laser to see what combination of power, speed and passes gets you the depths you’re looking for.


#3

If I want to cut a .25" deep by .25" wide groove into, say, delrin, how do I tell the laser to cut only .25" deep? How does it not cut deeper than .25"?

[…] if I want to cut all the way through a .75" thick piece of delrin, does GF know when it’s all the way through because I told GF it how thick the material is that it’s about to cut?

Glowforge Doesn’t ‘know’ in the same way that a CNC mill would “know”. Glowforge knows it’s location, speed, power, focus, and so on, but the actual cut amount is an (in)direct result of those parameters. This is why proofgrade and the settings derived are so important - for a given material, say 1/4 maple, a certain combination of settings might cut through perfectly, but on another piece not be sufficient, depending on the composition. Proofgrade just tries to take as much as the material deviation out of the equation as possible. For everything else, its simply comes down to testing to see what works.


#5

Ok, got it. So the power setting is the Thing.

So if the need is to cut all the way through some material, I’m guessing the answer isn’t automatically to apply the “max power” setting because you might get unwanted results like burning or melting.

Does the proofgrade stuff have info included online that says, in effect, “to cut through this completely, use X setting,” or “to cut a .25” deep groove into this, use Y setting"?


#7

Set up an excel sheet to track material settings on. You need Material name (I’d even break it down to supplier for similar materials), Thickness, Cut power/Speed, Score power/speed, and Engraving power/speed. Once you figure out the setting for a non proof grade material, update the excel sheet with your results for quick referencing.


#8

Currently Proofgrade materials supply 5 settings:

  • cut all the way through
  • deep score
  • light score
  • dark engrave
  • light engrave

For anything else you can choose “manual engrave” or “manual cut” to adjust the power/speed to your desired values. Some experimentation will be needed to get scores to a particular depth.

There’s a greyed out “3D Engrave” option for Proofgrade that will in the future allow for engravings that remove material to various depths (possibly using multiple passes with different focal lengths) but there hasn’t been a lot of detail released yet about that. But I imagine it could be used for your .25" deep by .25" wide groove once it’s enabled.

I wouldn’t be surprised to see depth-calibrated scoring for Proofgrade in a future software update as well, but they haven’t made any announcements about any such feature.

For non-Proofgrade materials you just get the manual cut/engrave settings.


#9

Changing LPI will also modify depth. The higher the LPI the deeper for a given power/speed setting. That’s because the laser will overlap previous passes of the head which effectively delivers more power somewhat akin to making a second or third full pass of the file.

You can see an example of that by looking at the settings for a PG light vs PG dark engrave.


#10

Very helpful info! Much appreciated!


#11

And one other thing–it really is essential to have calipers to do all that measuring with. It just can’t be done with rulers and such.


#12

If I want to engrave Proofgrade maple plywood to 1/2 its thickness to make a lap joint, I do 340 lpi, 700 speed and 60% power at 3 passes. That makes four variables to control for very specific effect of having an even surface and not having a real bad char to clean off, plus a little more out of the depth to ensure that nothing stands proud (which is important to the design of the little roll stamp box I made).

I discovered this by many test engraves, which I had to do three times with pre-release power profile changes and then to final production unit.

Your needs may require something else, but this is what works for me that I can rely on.

So to re-iterate, the laser can’t know it has cut through deep enough. You have to do some tests to see. I did quite a few on some .43" acrylic to see how depth works and what happens on successive passes. Learned a lot for that.

Cardboard was a fun test to, especially depending on the design, and the orientation of the corrugations, it behaved differently. but what is cool is engrave the top layer off of cardboard and leaving the corrugations intact as a design element.

Start at highest speed and lowest power (which seems to automatically get filled in for non PG materials when choosing an operation. Then test by changing one variable.


#13

Will do, Marmak3261. It sounds like learning this device will be similar to learning the Silhouette Portrait cutter. Depth (power) and Speed vs. Material used.


#14

Oh yes. I forgot focus too for a variable. In acrylic a focus higher than the surface leaves a nice mottled effect and de-emphasizes the raster lines.