Couple General Laser Questions

  1. What is the difference in engraving a Raster and a Vector in respect to speed and power.
  2. How much of a difference/affect could there be when the laser is 2mm out of focus, with 50.8 Focal Length. (I guess most K40’s).
  1. Raster Engraving engraves as the head scans side-to side as the head steps down in the y-direction. Vector engraving means the head follows a line as it engraves.
    You usually use higher power and higher speeds with raster engraving ( Typically 200-400 mm/s and 6-9mA). While vector engraving typically uses 15-30mm/s and 4-5mA.

  2. How much focus effects your engraving depends on how small the details you are trying to engrave. If you are trying to engrave a photo quality picture then you want the focus to right at the surface of the work piece to get the finest details. If your details are bigger then you can be out of focus more. In my case I typically engrave and cut without changing focus so my focus is set halfway into the work pieces for the best cutting. So for 3mm material that means the focus is 1.5mm below the surface and I still get good detail engraving.

The beam actually has a waist and the length of the waist, or depth of focus, is lens dependent. The longer the focal length the great the length of the waist.

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Thanks for the reply.
I guess maybe I didn’t get my thought across on question one. Why do the two require different power and speed, even with raster isn’t it basically just burning a line left and right just like a vector line of the same length.

You usually have one fast axis which you use for raster engraving.

The other axis usually isn’t nearly as fast. That’s why vector engraving must be done at a much lower speed.

However, depending on the design, vector engraving may be still a lot faster. E.g. if there are a few lines spread across a fairly large area, scanning across all of that space would waste a lot of time.

If you aren’t sure which option to pick, check the time estimates. If you do larger batches, try both options. See which one is faster and which looks better. Hopefully, the fast version looks just as good. Or maybe you can make it look just as good if you tweak it a bit. For tweaking, engraving a small area with some representative details is good enough. You usually don’t need the whole thing for that.

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As I mentioned before, raster and vector engraving operate differently. Vector engraving is basically the same as a cutting operation abet done at lower power and speed.

Raster engraving say a thin single line circle is not efficient as it has to cover the open area of the circle to get from side to the other. With vector engraving the the laser just follows the line of the circle.

As @tomatsu mentioned raster engraving is just fast in one direction, x, while vector engraving is done at the same speed to both the x and y directions. Laser engravers, especially the K40, are not really suitable for high speed engraving in both directions simultaneously. You tend to get artifacts in the engraving due to head bounce caused by the rapid change in momentum from the x to y direction. Since you have to vector engrave slower then you need to lower the power to compensate or your engraving detail will get blown out.

Higher end laser engraver could probably do it and you would need better control software that can change the acceleration and laser power simultaneously.

Raster engraving and vector engraving are just two different tools with different path generated operations. You could fill engrave an image with vector engraving, but you would need software that would generate the appropriate operation paths.

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If using Lightburn, they added “Offset Fill” which will operate similar to a vector operation for something like a image of a circle outline.

The real lessons here is to know what are the differences between a vector and an image. ie a vector is a mathematically described line/feature while an image is a grid of colored dots/pixels.
Your software will generate GCode to follow the lines/features of the vectors but you can’t do that with grid of dots so scanning back and forth is how the GCode is produced to handle images.

The next thing to understand is that the effect on your material is all based on how much “energy” can be put into the material during a period of time AND the lasers are not instantaneously turned on/off. A laser turning on/off needs a little time to get the same energy/burn as a laser which is already on.

There are hundreds of pages of these types of explanations out there in more and less depth so it is highly recommended to google for these things and see what others have posted. There are even professionally done pages since every laser customer needs to know these things and understand them so lots of laser manufacturers or resellers have covered these topics in detail.

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Yea I read a few, and some seemed like they had conflicting information. I understand clearly the difference between a raster and vector, was just trying to understand the difference in speed and power and how I can calculate my cut layers when I have both types in my project in Lightburn.

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Good to hear you are out researching but yes, you can also find conflicting information and have to filter what you find. Regarding speeds and power levels there really is not any way for someone to tell you use X speed and Y power for Z material since every laser is at different levels of wear, every laser is operated at differing temperatures and every material( especially woods ) are different densities and opacity. And air assist creates differences too.

Since you’re in the K40 category, you at least don’t have to worry or notice power changes in X vs Y directions( due to non-circular dot shape ).

Experimental feedback will be your best guide and where you start with your settings can help or hinder depending on how close your machine and material matches those of the person/site where you got the starting point settings.

It all boils down to how to get the amount of power into the material for the effect your want. But to help you learn the most, please do the ramp test and determine your ideal focal point and create a jig to repeatedly get that focal distance match for every material you work with. An out of focus beam will not provide the same results as when in focus and all these variations can become frustrating tried to get repeatable results.

It really has an artistic element to it but for those like me who like things less analog, reducing and eliminating variability goes a long way to getting good results.

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