Burn Test Pattern Tab
The first tab in the laser tool calibration window is called the “Burn test pattern” tab.
Here are the steps that you need to do, in the order you need to do them, to calibrate your laser tool. Keep in mind there are four tabs in this window and you’ll need to move through all four to complete your laser tool calibration. This is tab #1.
- Notice the laser tool name is displayed at the top of this first tab. A reminder of which laser tool you are calibrating. While this may sound obvious, when you get going creating a laser tool for up/down burning and another for 45 degrees burning, etc., you’ll appreciate this laser tool name displaying to remind of which one you’re working on.
- Radio Buttons. Since we’re covering Grayscale engraving at the moment, we’ll click the Grayscale radio button. That will ‘set’ that kind of engraving this laser tool will be used for: Grayscale.
- Burn Direction. Decide the direction you want this laser tool to work: there are three choices: up/down, 45 degrees and left/right. Depending on what kind of wood you are using, most likely one of these directions will produce better engraving quality than the other two.
You’ll have to test and experiment. My experience has been that burning against the grain has produced the best quality for most of the woods I have tested. 45 degrees is next best and burning with the grain has always shown the poorest quality. So, I would start with the up/down direction (assuming you lay down your wood with its grain running left/right as I do).
- Laser Beam Diameter. You’ll want to find the laser beam diameter (for your laser power and wood material) that will allow you to burn a 16 line group such that each line touches the previous line burn. You don’t want the lines too close together and you don’t want them too far apart such that you can see un-burned gaps between the line burns.
In my testing, this works out to be about 0.16mm or 0.18mm or 0.20mm, depending on what wood I’m working with.
So, to start this process, set a laser beam diameter of 0.30mm and click the Burn dark test line link. Here, you are looking to see if you can even see the line burn at all. Adjust the light feed rate until you can comfortably see a single medium shade line burn on the wood. Note that we are not calibrating the laser tool yet.
Once you can burn a medium single line and actually see it, click the Burn dark block link and watch the laser burn 16 lines in a group.
At this point, you want to see white gaps between the lines.
(picture goes here)
Now, start reducing the laser beam diameter by 0.02mm until your 16 line group burn shows each burn line touching the next one.
Now, you’ve just calibrated the laser beam diameter for this laser tool and laser direction!
- Light Feed Rate. As will be explained shortly, do his test before you do the dark burn test.
You will need to find your ‘light’ GS shade color. Use this spin button (light feed rate) to change the feed rate as you burn 16 light line blocks. The idea here is to get a nice light burn.
(pictures here to show examples)
For the light shading burn work, there is a trap: if you’re working with porous woods such as Craft Plywood or Baltic Birch, their surfaces are very uneven and it will be difficult to get a light line to burn for the whole length of the line. You’ll finally get the light shading color that looks good to your eye, but you’ll see ‘paint chipping’ in the 16 line burn block. Like this picture shows:
So what do you do? You have reduce the feed rate and slow down the laser head movement in order to be able to burn a whole line completely. Find the speed that will allow the 16 group line burn to remove the ‘paint chipping’. This will, unfortunately, produce a darker ‘light’ shading color than you’d like, but the paint chipping will have been eliminated. Your over all engraving will be darker. This is why these porous woods are not the best choice for engraving.
Note that you won’t run into this ‘paint chipping ‘ problem using light colored hard woods.
- Dark Feed Rate. Next up, you will need to find your ‘black’ GS shade color. Use this spin button to change the feed rate as you burn a 16 line dark block.
Since you’ve already set the laser power for the light shade burning, DO NOT adjust laser power here. If you adjust laser power here, it will void your light shading burn tests and you’ll have to re-do them.
The idea here is to get a nice dark burn. But don’t burn the wood too deep. Don’t burn the wood so much that around the burn area there is soot and ash residue.
With experience, you’ll learn what ‘dark’ shade will work for your ‘black’ square of your 16 GS shades.
- Power Level Percent. This section is just FYI. When burning the light shading lines, you may get the laser feed speeds close to or over 3000mm/min. And you’re light shading is still too dark. This is about where you might want to start reducing the laser power. Setting laser movement speeds > 3000 will tend to jerk and move the entire laser frame around on your work bench. So my advice is not to get too much above the 3000mm/min speed, but if your light shade is still too dark, then start to reduce your laser power.
Note that it is for this reason that you should start with the light shading tests and then once set, do the dark shading tests.
- Bias (Gamma). The Bias value (commonly known as Gamma Correction in the graphics world) allows you to compensate for materials that do not burn in a linear way. For example, doubling the feed rate may not result in a burn that is exactly twice as light.
The Bias value does not change the darkest or lightest shade but it controls how the shades in-between are distributed.
Values less than 1 will shift the shades towards the lightest shade. Values greater then 1 will shift them towards the darkest shade.
If the test pattern does not have an even distribution of shades (perhaps the squares are mostly dark but then just a few at the end get light very quickly) then you can use the bias to correct this.
The best way to see if any bias correction is needed (and if so, how much) is to use the bias adjustment tab. See the 4th tab for full details.
- Burn Test Pattern Button. Clicking this button will burn the 16 shade GS pattern. This pattern is what you will take a picture of and load into BCL so it can analyze it mathematically and plot each one of the 16 shade values on a graph.
- Connected Button. You can connect and disconnect from your laser machine using this button, without having to close this calibration window. On purpose, this window is modal, which means you cannot access any other part of BCL while this window is open.
- Stop Button. Clicking this button will stop the laser machine relatively fast. You may have to click it twice. If you don’t want to wait for the GS pattern to finish burning, you can stop it and then re-connect, make any adjustments and start the pattern burn again.
- Jog Arrows. You may need to move the laser head to an unused spot on your wood to continue test burning. Again, because you can’t access the main BCL jogging tab, you can jog from inside this window itself.