4095 Step Grayscale

[rwensley]

Okay. I have these settings in grbl now

Z max depth = 1 mm
Z step/mm 4095
Z Max feed rate = 439.5604 mm/min = 7.326 mm/sec
The step frequency = 30kHz
So travel time full scale should be 55.9 mS

and I am making a test piece. All seems to be working well at this point. Now it will be a matter of tweaking the settings to get the best picture.

[Picengravertoo]

Hi Ron,

There is always an interest in different ways to control the laser's intensity for engraving images, so please let us know how it works out.

Thanks.
Jeff

[rwensley]

Jeff,

I am close to having a good engraving. Right now I am not getting the lighter shades so the result is mostly dark and darker. I can see the image but the contrast is very poor. I suspect that it has to do with the X federate. So I am moving this up and retesting. Working for a living gets in the way however. I also have FRC set at 35% in hopes that will help.

Any pointers to improve contrast are welcome. Actually all pointers are welcome. The *.bmp image has very high clear and crisp contrast covering all shades of gray from white to black. So it is a machine setting issue. <I hope>

The diode I am using does not start burning the wood utill about -0.2 mm on the Z axis. So I have set that as the minimum with the thought that it would eliminate the wind up for 0 to -0.2. Still playing.

Ron

[Picengravertoo]

Ron,

How do you have your X&Y accels and junction deviation set? Here is how we have our grbl machines set.

$11=0.005 (junction deviation, mm)
$120=12000.000 (x accel, mm/sec^2)
$121=12000.000 (y accel, mm/sec^2)

A higher FRC percentage will make the over all shades burn darker, so try using 20% instead. The smaller the focal point is and less the Pixel Resolution (Step over) used, it will engrave with more sharpness & contrast.

Jeff

[rwensley]

Jeff,

Thanks for the feedback on the settings. Virtually eliminating acceleration is a clear idea
It is getting closer. I have the X federate at 750 and the pixel res at 0.2. Now tweaking that down to remove banding/lines.
It is a pain getting the settings the first time but once I have them for this material it will be easier to just start.

When I get a decent gray scale engraved I will post it with all settings and machine details.

Ron

[rwensley]

Me bethinks' I need a different diode. My pixel resolution is just too high 0.21mm to get great results. It works great for line art but not so much with gray scale.

[Picengravertoo]

A better lens could get you a smaller focal point. What Laser Diode do you have?

[rwensley]

I am using a NUBM44 it has a large spot measured at 28 mm from the lens the main spot is 0.776 mm wide and 0.097mm high plus the side lobes.

I have ordered a different lens for it. I have also ordered a NDB7875. We shall see.

[Picengravertoo]

Ok, I have one of the NUBM44 6W and I can't get a small enough focal point to engrave any detailed photos no matter what lens I use. The divergence is too large and will only focus to an oval shape. I only use it for cutting and 3D engraving. The NDB7875 is much better for laser engraving detailed photos with a 3 element glass lens.