Engraving Using Smoothieware Questions

Machine: _K40
Board: _Cohesion3D Laserboard/GLCD
Firmware: _Smoothie
Problem/ Question: I have a few questions that I have been searching for. Sorry if these are obvious to others. I have had my K40 up and running with C3D for about a week:

  1. Does the C3D board use USB 2.0 or 3.0 and is there any advantage to USB 3.0 for engraving? My computer currently only has 2.0.

  2. Is there any advantage from a speed perspective or less engraving issues of saving the GCode to the SD card and running it off the GLCD?

  3. Is the new Smoothieware raster fix truly an improvement to GCode processing speed from 1
    ms to .25ms? I am engraving at .05mm so I am thinking maximum speed at this resolution is 200mm/sec. Is this a true statement? Following this rationale:

At 100mm/sec and 1 ms update(Old Smoothie), max res. = (100mm/sec) x .001 sec. = .1mm
At 200mm/sec and .25ms update(New Smoothieware) max res. = (200mm/sec) x .00025sec = .05mm

  1. Is .05mm resolution overkill for engraving? Can you really see a difference between .05 and .1mm?

  2. When I create a grayscale pattern in lightburn, the laser engraves 1 box at a time. Is there a way to combine these images and have them engrave all the way across the row for each line?

  3. Does anyone have recommendations for a true grayscale image that I can test for Raster engraving. The test matrix uses fill mode but it is not really representative of raster engraving. I would like to load and test and continuous gradient from left to right across my work area?

Sorry for so many questions but these are the list of issues I have tried researching to no avail.

Thanks Guys

1 - The laserboard itself is USB 2.0. There’s no real advantage to 3.0 in this application since it’s sending relatively low-speed serial data to the controller for processing. The bottleneck is the machine in physical motion, and the rate at which the processor on the laserboard can execute commands, not the host interface.

2 - There, likewise, should be no difference in speed when using SD or USB. Running jobs from the SD card is a feature included for convenience (e.g. you don’t have a computer always connected to the laser).

3 - As far as the smoothieware patch goes - someone else (Oz, maybe?) will have to detail what actually went on there. I’m admittedly not super familiar with the implementation details there.

4 - it depends a lot on the material, the focal length of the lens you’re using, relative tube output strength, and an overwhelming variety of other factors. Be prepared to play around with it and see what works best for your particular application. On a K40 with stock optics and bed, there probably isn’t much reason to try for more granularity than 0.1mm (in fact, that might even be pushing it a little).

5 - this is likely a setting you can tweak in lightburn. If all the shapes you want to engrave at once are on the same layer, open the layer properties and make sure that ‘scan all objects at once’ is checked (or similar, I don’t have a copy of LB on this machine to get the exact wording). If they’re on different layers, combine them into one layer and that should help. If you want to scan different objects at different intensities on the same layer, that’s a little more complicated but also possible. You do that in the Shape Properties box for that particular object and can set the power as a percentage of maximum for the layer (e.g. if the layer settings have max power at 50%, 100% in the Shape Properties box will be 50% true power, 50% in the Shape Properties box will be 25% true, etc.). To my knowledge there’s no way to scan objects on different layers simultaneously (this is due to the top-down layer priority and how the movement planner interacts with that). Note that for some jobs, scanning the shapes individually might actually be faster. The preview window will help you determine this.

6 - greyscale mode is difficult to perfect. Really difficult. It’ll take a long time and a lot of material to dial the settings in just right. There’s no real magic image or anything that can help you tune it - the settings are going to be different for each image and each material on which you engrave it. Once you get to know your machine and the settings a bit better, it’ll be easier to dial it in, but expect a to spend a few hours and a lot of cursing getting it just so. :slight_smile: To be honest, I kinda gave up on greyscale and use one of the dithered modes to get images onto my projects. It gets me far superior results to greyscale in most cases. That won’t help however, if you’re trying to do e.g. 3D engraving - you really do need greyscale for that, and it’s definitely more art than science.

Just play around with it :slight_smile: get some sacrificial material and see how it goes!

I’m going to agree with just about everything offered above (thanks @loather ! :slight_smile:) and add to your #3 and #4 the following:

In the new firmware release, ( Improved Raster Speed Firmware Update for Cohesion3D Boards! ) I talk about realistic expectations:

  • 0.1mm dot size = 254 DPI and 0.05mm dot size = 508 DPI.
  • The actual dot size of the K40 is around 0.1mm, so 254 to 300 DPI is a good range to work in.
  • You are not engraving at 500 DPI on a stock K40 unless you have possibly a lens with a shorter focus length, but more realistically a compound head.
  • Our testing of the new firmware went up to something like 240 mm/s at 254 DPI. If you go to 508 DPI, halve the max speed. Simple math for a simple rule of thumb.
  • A true test of the most severe “grayscale” - ie: the most dense change with the most amount of data to send to the controller is not actually an image processed as grayscale, but if I recall correctly, a simple background that is exactly 50% black/ white (gray) processed as a threshold dither. I can try to verify the accuracy of this if needed - not 100% sure if I am recalling correctly from 6+ months ago.

Having said all this, are these “issues” actual problems you are experiencing, or just a fun theoretical and educational exercise?
If actual issue, do tell of concrete problem so we can offer fix.
If theoretical, I recommend to just use the thing, within the parameters specified above, until you run into actual problems that need fixes, then post for help :slight_smile:

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Thanks, the questions related to usb raster speed, line width etc… were all related to problems with engraving images. I was getting splits, shifts, etc… I believe I have a much better handle on that now since those problem have disappeared.

The grayscale issue I am having is really kicking my butt. I have tried several different powers and create the 100 to 10% matrix of squares and always the same thing. The top end I can get dark but all the way down to 20% there is an almost Imperceivable change in darkness. The it goes light very fast. When I lower the power to a point just above where the grayscale starts to show up, same thing or I get to the point where my black is not dark anymore. It’s almost like the grayscale in the center of the spectrum is to dark always so the distribution of color always leans on the dark side. Wondering if tuning the pen would help but I don’t understand the science yet of what the pwm, 200 vs 400 actually does. This happens on more that one type of wood for me

Typo above. I meant tuning the pwm

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