Benbox Laser Machines/CO2 Lasers/3D Printers

The 0-1000 or 0-255 make no difference to the output, it's still an 8-bit PWM so 0-255 no matter what input value is used. Resolution or granularity of the signal doesn't change.

You can use 0-1000 or any max number you like within reason on any firmware by changing the Grbl parameter ($30).

The difference with the high frequency firmware is it uses a 7.8kHz PWM instead of the usual 1.0kHz, so you get a much shorter pulse width that repeats much more often.

I would get a replacement Nano and swap it out, that may resolve your issues.

I guess that's the newer version, and new higher price too.

If you are essentially putting a standard frame into the enclosure it would make more sense to use standard cables and an Eleks or Cronos board.

How do you adjust the focus (Z-axis)?

On my old K40 I installed a motor on the Z-bed so I could focus in T2Laser (that's where the Z-focus feature came from) but of course it had very limited XY size.

That's genius. It's about time they changed the K40 design, it's been basically the same for well over 10 years (I got mine in 2008).

I prefer the EleksMaker laser modules, 2.5W for engraving or 5.5W for cutting. The NEJE, AtomStack and Ortur modules sold as "30W" which is approximately 5.5W output are popular alternatives but you may sacrifce some lifetime. There are other generic modules that are cheaper but quality is varied.

+ should be 12VDC relative to GND but as the power supply is unregulated it could read 15VDC without a load, that's normal.
The signal (S) pin is a PWM TTL output.

Are you saying the signal pin has 15VDC or the +?

It depends on the wavelength of the laser, typically a CO2 will remove the pigment and leave white whereas a diode will just remove the surface. If you paint them white and then dark green you'll be able to remove the top layer revealing the white.

On tile I use 2 or 3 very thin coats and allow it to dry between applications, it gives a more consistent result than trying to cover the tile in a single thicker coat.

Using a resolution of 0.05 means the laser is passing over the same area 3 times, slightly offset each time as the beam is probably closer to 0.15 or more. I prefer to use a more practical resolution value that matches the spot size and reduce the feed rate but I know your method is also popular and I have seen some very good results.

Metal may not provide the same results as ceramic (tile) as the metal will absorb much of the energy (heat) and dissipate it before it can ablate the paint.